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Linux kernel mirror (for testing) git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git
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SPDX-License-Identifier: GPL-2.0/* * linux/ipc/sem.c * Copyright (C) 1992 Krishna Balasubramanian * Copyright (C) 1995 Eric Schenk, Bruno Haible * * /proc/sysvipc/sem support (c) 1999 Dragos Acostachioaie <dragos@iname.com> * * SMP-threaded, sysctl's added * (c) 1999 Manfred Spraul <manfred@colorfullife.com> * Enforced range limit on SEM_UNDO * (c) 2001 Red Hat Inc * Lockless wakeup * (c) 2003 Manfred Spraul <manfred@colorfullife.com> * (c) 2016 Davidlohr Bueso <dave@stgolabs.net> * Further wakeup optimizations, documentation * (c) 2010 Manfred Spraul <manfred@colorfullife.com> * * support for audit of ipc object properties and permission changes * Dustin Kirkland <dustin.kirkland@us.ibm.com> * * namespaces support * OpenVZ, SWsoft Inc. * Pavel Emelianov <xemul@openvz.org> * * Implementation notes: (May 2010) * This file implements System V semaphores. * * User space visible behavior: * - FIFO ordering for semop() operations (just FIFO, not starvation * protection) * - multiple semaphore operations that alter the same semaphore in * one semop() are handled. * - sem_ctime (time of last semctl()) is updated in the IPC_SET, SETVAL and * SETALL calls. * - two Linux specific semctl() commands: SEM_STAT, SEM_INFO. * - undo adjustments at process exit are limited to 0..SEMVMX. * - namespace are supported. * - SEMMSL, SEMMNS, SEMOPM and SEMMNI can be configured at runtime by writing * to /proc/sys/kernel/sem. * - statistics about the usage are reported in /proc/sysvipc/sem. * * Internals: * - scalability: * - all global variables are read-mostly. * - semop() calls and semctl(RMID) are synchronized by RCU. * - most operations do write operations (actually: spin_lock calls) to * the per-semaphore array structure. * Thus: Perfect SMP scaling between independent semaphore arrays. * If multiple semaphores in one array are used, then cache line * trashing on the semaphore array spinlock will limit the scaling. * - semncnt and semzcnt are calculated on demand in count_semcnt() * - the task that performs a successful semop() scans the list of all * sleeping tasks and completes any pending operations that can be fulfilled. * Semaphores are actively given to waiting tasks (necessary for FIFO). * (see update_queue()) * - To improve the scalability, the actual wake-up calls are performed after * dropping all locks. (see wake_up_sem_queue_prepare()) * - All work is done by the waker, the woken up task does not have to do * anything - not even acquiring a lock or dropping a refcount. * - A woken up task may not even touch the semaphore array anymore, it may * have been destroyed already by a semctl(RMID). * - UNDO values are stored in an array (one per process and per * semaphore array, lazily allocated). For backwards compatibility, multiple * modes for the UNDO variables are supported (per process, per thread) * (see copy_semundo, CLONE_SYSVSEM) * - There are two lists of the pending operations: a per-array list * and per-semaphore list (stored in the array). This allows to achieve FIFO * ordering without always scanning all pending operations. * The worst-case behavior is nevertheless O(N^2) for N wakeups. */
#include <linux/compat.h>#include <linux/slab.h>#include <linux/spinlock.h>#include <linux/init.h>#include <linux/proc_fs.h>#include <linux/time.h>#include <linux/security.h>#include <linux/syscalls.h>#include <linux/audit.h>#include <linux/capability.h>#include <linux/seq_file.h>#include <linux/rwsem.h>#include <linux/nsproxy.h>#include <linux/ipc_namespace.h>#include <linux/sched/wake_q.h>#include <linux/nospec.h>#include <linux/rhashtable.h>
#include <linux/uaccess.h>#include "util.h"
/* One semaphore structure for each semaphore in the system. */struct sem { int semval; /* current value */ /* * PID of the process that last modified the semaphore. For * Linux, specifically these are: * - semop * - semctl, via SETVAL and SETALL. * - at task exit when performing undo adjustments (see exit_sem). */ struct pid *sempid; spinlock_t lock; /* spinlock for fine-grained semtimedop */ struct list_head pending_alter; /* pending single-sop operations */ /* that alter the semaphore */ struct list_head pending_const; /* pending single-sop operations */ /* that do not alter the semaphore*/ time64_t sem_otime; /* candidate for sem_otime */} ____cacheline_aligned_in_smp;
/* One sem_array data structure for each set of semaphores in the system. */struct sem_array { struct kern_ipc_perm sem_perm; /* permissions .. see ipc.h */ time64_t sem_ctime; /* create/last semctl() time */ struct list_head pending_alter; /* pending operations */ /* that alter the array */ struct list_head pending_const; /* pending complex operations */ /* that do not alter semvals */ struct list_head list_id; /* undo requests on this array */ int sem_nsems; /* no. of semaphores in array */ int complex_count; /* pending complex operations */ unsigned int use_global_lock;/* >0: global lock required */
struct sem sems[];} __randomize_layout;
/* One queue for each sleeping process in the system. */struct sem_queue { struct list_head list; /* queue of pending operations */ struct task_struct *sleeper; /* this process */ struct sem_undo *undo; /* undo structure */ struct pid *pid; /* process id of requesting process */ int status; /* completion status of operation */ struct sembuf *sops; /* array of pending operations */ struct sembuf *blocking; /* the operation that blocked */ int nsops; /* number of operations */ bool alter; /* does *sops alter the array? */ bool dupsop; /* sops on more than one sem_num */};
/* Each task has a list of undo requests. They are executed automatically * when the process exits. */struct sem_undo { struct list_head list_proc; /* per-process list: * * all undos from one process * rcu protected */ struct rcu_head rcu; /* rcu struct for sem_undo */ struct sem_undo_list *ulp; /* back ptr to sem_undo_list */ struct list_head list_id; /* per semaphore array list: * all undos for one array */ int semid; /* semaphore set identifier */ short semadj[]; /* array of adjustments */ /* one per semaphore */};
/* sem_undo_list controls shared access to the list of sem_undo structures * that may be shared among all a CLONE_SYSVSEM task group. */struct sem_undo_list { refcount_t refcnt; spinlock_t lock; struct list_head list_proc;};
#define sem_ids(ns) ((ns)->ids[IPC_SEM_IDS])
static int newary(struct ipc_namespace *, struct ipc_params *);static void freeary(struct ipc_namespace *, struct kern_ipc_perm *);#ifdef CONFIG_PROC_FSstatic int sysvipc_sem_proc_show(struct seq_file *s, void *it);#endif
#define SEMMSL_FAST 256 /* 512 bytes on stack */#define SEMOPM_FAST 64 /* ~ 372 bytes on stack */
/* * Switching from the mode suitable for simple ops * to the mode for complex ops is costly. Therefore: * use some hysteresis */#define USE_GLOBAL_LOCK_HYSTERESIS 10
/* * Locking: * a) global sem_lock() for read/write * sem_undo.id_next, * sem_array.complex_count, * sem_array.pending{_alter,_const}, * sem_array.sem_undo * * b) global or semaphore sem_lock() for read/write: * sem_array.sems[i].pending_{const,alter}: * * c) special: * sem_undo_list.list_proc: * * undo_list->lock for write * * rcu for read * use_global_lock: * * global sem_lock() for write * * either local or global sem_lock() for read. * * Memory ordering: * Most ordering is enforced by using spin_lock() and spin_unlock(). * * Exceptions: * 1) use_global_lock: (SEM_BARRIER_1) * Setting it from non-zero to 0 is a RELEASE, this is ensured by * using smp_store_release(): Immediately after setting it to 0, * a simple op can start. * Testing if it is non-zero is an ACQUIRE, this is ensured by using * smp_load_acquire(). * Setting it from 0 to non-zero must be ordered with regards to * this smp_load_acquire(), this is guaranteed because the smp_load_acquire() * is inside a spin_lock() and after a write from 0 to non-zero a * spin_lock()+spin_unlock() is done. * To prevent the compiler/cpu temporarily writing 0 to use_global_lock, * READ_ONCE()/WRITE_ONCE() is used. * * 2) queue.status: (SEM_BARRIER_2) * Initialization is done while holding sem_lock(), so no further barrier is * required. * Setting it to a result code is a RELEASE, this is ensured by both a * smp_store_release() (for case a) and while holding sem_lock() * (for case b). * The ACQUIRE when reading the result code without holding sem_lock() is * achieved by using READ_ONCE() + smp_acquire__after_ctrl_dep(). * (case a above). * Reading the result code while holding sem_lock() needs no further barriers, * the locks inside sem_lock() enforce ordering (case b above) * * 3) current->state: * current->state is set to TASK_INTERRUPTIBLE while holding sem_lock(). * The wakeup is handled using the wake_q infrastructure. wake_q wakeups may * happen immediately after calling wake_q_add. As wake_q_add_safe() is called * when holding sem_lock(), no further barriers are required. * * See also ipc/mqueue.c for more details on the covered races. */
#define sc_semmsl sem_ctls[0]#define sc_semmns sem_ctls[1]#define sc_semopm sem_ctls[2]#define sc_semmni sem_ctls[3]
void sem_init_ns(struct ipc_namespace *ns){ ns->sc_semmsl = SEMMSL; ns->sc_semmns = SEMMNS; ns->sc_semopm = SEMOPM; ns->sc_semmni = SEMMNI; ns->used_sems = 0; ipc_init_ids(&ns->ids[IPC_SEM_IDS]);}
#ifdef CONFIG_IPC_NSvoid sem_exit_ns(struct ipc_namespace *ns){ free_ipcs(ns, &sem_ids(ns), freeary); idr_destroy(&ns->ids[IPC_SEM_IDS].ipcs_idr); rhashtable_destroy(&ns->ids[IPC_SEM_IDS].key_ht);}#endif
void __init sem_init(void){ sem_init_ns(&init_ipc_ns); ipc_init_proc_interface("sysvipc/sem", " key semid perms nsems uid gid cuid cgid otime ctime\n", IPC_SEM_IDS, sysvipc_sem_proc_show);}
/** * unmerge_queues - unmerge queues, if possible. * @sma: semaphore array * * The function unmerges the wait queues if complex_count is 0. * It must be called prior to dropping the global semaphore array lock. */static void unmerge_queues(struct sem_array *sma){ struct sem_queue *q, *tq;
/* complex operations still around? */ if (sma->complex_count) return; /* * We will switch back to simple mode. * Move all pending operation back into the per-semaphore * queues. */ list_for_each_entry_safe(q, tq, &sma->pending_alter, list) { struct sem *curr; curr = &sma->sems[q->sops[0].sem_num];
list_add_tail(&q->list, &curr->pending_alter); } INIT_LIST_HEAD(&sma->pending_alter);}
/** * merge_queues - merge single semop queues into global queue * @sma: semaphore array * * This function merges all per-semaphore queues into the global queue. * It is necessary to achieve FIFO ordering for the pending single-sop * operations when a multi-semop operation must sleep. * Only the alter operations must be moved, the const operations can stay. */static void merge_queues(struct sem_array *sma){ int i; for (i = 0; i < sma->sem_nsems; i++) { struct sem *sem = &sma->sems[i];
list_splice_init(&sem->pending_alter, &sma->pending_alter); }}
static void sem_rcu_free(struct rcu_head *head){ struct kern_ipc_perm *p = container_of(head, struct kern_ipc_perm, rcu); struct sem_array *sma = container_of(p, struct sem_array, sem_perm);
security_sem_free(&sma->sem_perm); kvfree(sma);}
/* * Enter the mode suitable for non-simple operations: * Caller must own sem_perm.lock. */static void complexmode_enter(struct sem_array *sma){ int i; struct sem *sem;
if (sma->use_global_lock > 0) { /* * We are already in global lock mode. * Nothing to do, just reset the * counter until we return to simple mode. */ WRITE_ONCE(sma->use_global_lock, USE_GLOBAL_LOCK_HYSTERESIS); return; } WRITE_ONCE(sma->use_global_lock, USE_GLOBAL_LOCK_HYSTERESIS);
for (i = 0; i < sma->sem_nsems; i++) { sem = &sma->sems[i]; spin_lock(&sem->lock); spin_unlock(&sem->lock); }}
/* * Try to leave the mode that disallows simple operations: * Caller must own sem_perm.lock. */static void complexmode_tryleave(struct sem_array *sma){ if (sma->complex_count) { /* Complex ops are sleeping. * We must stay in complex mode */ return; } if (sma->use_global_lock == 1) {
/* See SEM_BARRIER_1 for purpose/pairing */ smp_store_release(&sma->use_global_lock, 0); } else { WRITE_ONCE(sma->use_global_lock, sma->use_global_lock-1); }}
#define SEM_GLOBAL_LOCK (-1)/* * If the request contains only one semaphore operation, and there are * no complex transactions pending, lock only the semaphore involved. * Otherwise, lock the entire semaphore array, since we either have * multiple semaphores in our own semops, or we need to look at * semaphores from other pending complex operations. */static inline int sem_lock(struct sem_array *sma, struct sembuf *sops, int nsops){ struct sem *sem; int idx;
if (nsops != 1) { /* Complex operation - acquire a full lock */ ipc_lock_object(&sma->sem_perm);
/* Prevent parallel simple ops */ complexmode_enter(sma); return SEM_GLOBAL_LOCK; }
/* * Only one semaphore affected - try to optimize locking. * Optimized locking is possible if no complex operation * is either enqueued or processed right now. * * Both facts are tracked by use_global_mode. */ idx = array_index_nospec(sops->sem_num, sma->sem_nsems); sem = &sma->sems[idx];
/* * Initial check for use_global_lock. Just an optimization, * no locking, no memory barrier. */ if (!READ_ONCE(sma->use_global_lock)) { /* * It appears that no complex operation is around. * Acquire the per-semaphore lock. */ spin_lock(&sem->lock);
/* see SEM_BARRIER_1 for purpose/pairing */ if (!smp_load_acquire(&sma->use_global_lock)) { /* fast path successful! */ return sops->sem_num; } spin_unlock(&sem->lock); }
/* slow path: acquire the full lock */ ipc_lock_object(&sma->sem_perm);
if (sma->use_global_lock == 0) { /* * The use_global_lock mode ended while we waited for * sma->sem_perm.lock. Thus we must switch to locking * with sem->lock. * Unlike in the fast path, there is no need to recheck * sma->use_global_lock after we have acquired sem->lock: * We own sma->sem_perm.lock, thus use_global_lock cannot * change. */ spin_lock(&sem->lock);
ipc_unlock_object(&sma->sem_perm); return sops->sem_num; } else { /* * Not a false alarm, thus continue to use the global lock * mode. No need for complexmode_enter(), this was done by * the caller that has set use_global_mode to non-zero. */ return SEM_GLOBAL_LOCK; }}
static inline void sem_unlock(struct sem_array *sma, int locknum){ if (locknum == SEM_GLOBAL_LOCK) { unmerge_queues(sma); complexmode_tryleave(sma); ipc_unlock_object(&sma->sem_perm); } else { struct sem *sem = &sma->sems[locknum]; spin_unlock(&sem->lock); }}
/* * sem_lock_(check_) routines are called in the paths where the rwsem * is not held. * * The caller holds the RCU read lock. */static inline struct sem_array *sem_obtain_object(struct ipc_namespace *ns, int id){ struct kern_ipc_perm *ipcp = ipc_obtain_object_idr(&sem_ids(ns), id);
if (IS_ERR(ipcp)) return ERR_CAST(ipcp);
return container_of(ipcp, struct sem_array, sem_perm);}
static inline struct sem_array *sem_obtain_object_check(struct ipc_namespace *ns, int id){ struct kern_ipc_perm *ipcp = ipc_obtain_object_check(&sem_ids(ns), id);
if (IS_ERR(ipcp)) return ERR_CAST(ipcp);
return container_of(ipcp, struct sem_array, sem_perm);}
static inline void sem_lock_and_putref(struct sem_array *sma){ sem_lock(sma, NULL, -1); ipc_rcu_putref(&sma->sem_perm, sem_rcu_free);}
static inline void sem_rmid(struct ipc_namespace *ns, struct sem_array *s){ ipc_rmid(&sem_ids(ns), &s->sem_perm);}
static struct sem_array *sem_alloc(size_t nsems){ struct sem_array *sma;
if (nsems > (INT_MAX - sizeof(*sma)) / sizeof(sma->sems[0])) return NULL;
sma = kvzalloc_flex(*sma, sems, nsems, GFP_KERNEL_ACCOUNT); if (unlikely(!sma)) return NULL;
return sma;}
/** * newary - Create a new semaphore set * @ns: namespace * @params: ptr to the structure that contains key, semflg and nsems * * Called with sem_ids.rwsem held (as a writer) */static int newary(struct ipc_namespace *ns, struct ipc_params *params){ int retval; struct sem_array *sma; key_t key = params->key; int nsems = params->u.nsems; int semflg = params->flg; int i;
if (!nsems) return -EINVAL; if (ns->used_sems + nsems > ns->sc_semmns) return -ENOSPC;
sma = sem_alloc(nsems); if (!sma) return -ENOMEM;
sma->sem_perm.mode = (semflg & S_IRWXUGO); sma->sem_perm.key = key;
sma->sem_perm.security = NULL; retval = security_sem_alloc(&sma->sem_perm); if (retval) { kvfree(sma); return retval; }
for (i = 0; i < nsems; i++) { INIT_LIST_HEAD(&sma->sems[i].pending_alter); INIT_LIST_HEAD(&sma->sems[i].pending_const); spin_lock_init(&sma->sems[i].lock); }
sma->complex_count = 0; sma->use_global_lock = USE_GLOBAL_LOCK_HYSTERESIS; INIT_LIST_HEAD(&sma->pending_alter); INIT_LIST_HEAD(&sma->pending_const); INIT_LIST_HEAD(&sma->list_id); sma->sem_nsems = nsems; sma->sem_ctime = ktime_get_real_seconds();
/* ipc_addid() locks sma upon success. */ retval = ipc_addid(&sem_ids(ns), &sma->sem_perm, ns->sc_semmni); if (retval < 0) { ipc_rcu_putref(&sma->sem_perm, sem_rcu_free); return retval; } ns->used_sems += nsems;
sem_unlock(sma, -1); rcu_read_unlock();
return sma->sem_perm.id;}
/* * Called with sem_ids.rwsem and ipcp locked. */static int sem_more_checks(struct kern_ipc_perm *ipcp, struct ipc_params *params){ struct sem_array *sma;
sma = container_of(ipcp, struct sem_array, sem_perm); if (params->u.nsems > sma->sem_nsems) return -EINVAL;
return 0;}
long ksys_semget(key_t key, int nsems, int semflg){ struct ipc_namespace *ns; static const struct ipc_ops sem_ops = { .getnew = newary, .associate = security_sem_associate, .more_checks = sem_more_checks, }; struct ipc_params sem_params;
ns = current->nsproxy->ipc_ns;
if (nsems < 0 || nsems > ns->sc_semmsl) return -EINVAL;
sem_params.key = key; sem_params.flg = semflg; sem_params.u.nsems = nsems;
return ipcget(ns, &sem_ids(ns), &sem_ops, &sem_params);}
SYSCALL_DEFINE3(semget, key_t, key, int, nsems, int, semflg){ return ksys_semget(key, nsems, semflg);}
/** * perform_atomic_semop[_slow] - Attempt to perform semaphore * operations on a given array. * @sma: semaphore array * @q: struct sem_queue that describes the operation * * Caller blocking are as follows, based the value * indicated by the semaphore operation (sem_op): * * (1) >0 never blocks. * (2) 0 (wait-for-zero operation): semval is non-zero. * (3) <0 attempting to decrement semval to a value smaller than zero. * * Returns 0 if the operation was possible. * Returns 1 if the operation is impossible, the caller must sleep. * Returns <0 for error codes. */static int perform_atomic_semop_slow(struct sem_array *sma, struct sem_queue *q){ int result, sem_op, nsops; struct pid *pid; struct sembuf *sop; struct sem *curr; struct sembuf *sops; struct sem_undo *un;
sops = q->sops; nsops = q->nsops; un = q->undo;
for (sop = sops; sop < sops + nsops; sop++) { int idx = array_index_nospec(sop->sem_num, sma->sem_nsems); curr = &sma->sems[idx]; sem_op = sop->sem_op; result = curr->semval;
if (!sem_op && result) goto would_block;
result += sem_op; if (result < 0) goto would_block; if (result > SEMVMX) goto out_of_range;
if (sop->sem_flg & SEM_UNDO) { int undo = un->semadj[sop->sem_num] - sem_op; /* Exceeding the undo range is an error. */ if (undo < (-SEMAEM - 1) || undo > SEMAEM) goto out_of_range; un->semadj[sop->sem_num] = undo; }
curr->semval = result; }
sop--; pid = q->pid; while (sop >= sops) { ipc_update_pid(&sma->sems[sop->sem_num].sempid, pid); sop--; }
return 0;
out_of_range: result = -ERANGE; goto undo;
would_block: q->blocking = sop;
if (sop->sem_flg & IPC_NOWAIT) result = -EAGAIN; else result = 1;
undo: sop--; while (sop >= sops) { sem_op = sop->sem_op; sma->sems[sop->sem_num].semval -= sem_op; if (sop->sem_flg & SEM_UNDO) un->semadj[sop->sem_num] += sem_op; sop--; }
return result;}
static int perform_atomic_semop(struct sem_array *sma, struct sem_queue *q){ int result, sem_op, nsops; struct sembuf *sop; struct sem *curr; struct sembuf *sops; struct sem_undo *un;
sops = q->sops; nsops = q->nsops; un = q->undo;
if (unlikely(q->dupsop)) return perform_atomic_semop_slow(sma, q);
/* * We scan the semaphore set twice, first to ensure that the entire * operation can succeed, therefore avoiding any pointless writes * to shared memory and having to undo such changes in order to block * until the operations can go through. */ for (sop = sops; sop < sops + nsops; sop++) { int idx = array_index_nospec(sop->sem_num, sma->sem_nsems);
curr = &sma->sems[idx]; sem_op = sop->sem_op; result = curr->semval;
if (!sem_op && result) goto would_block; /* wait-for-zero */
result += sem_op; if (result < 0) goto would_block;
if (result > SEMVMX) return -ERANGE;
if (sop->sem_flg & SEM_UNDO) { int undo = un->semadj[sop->sem_num] - sem_op;
/* Exceeding the undo range is an error. */ if (undo < (-SEMAEM - 1) || undo > SEMAEM) return -ERANGE; } }
for (sop = sops; sop < sops + nsops; sop++) { curr = &sma->sems[sop->sem_num]; sem_op = sop->sem_op;
if (sop->sem_flg & SEM_UNDO) { int undo = un->semadj[sop->sem_num] - sem_op;
un->semadj[sop->sem_num] = undo; } curr->semval += sem_op; ipc_update_pid(&curr->sempid, q->pid); }
return 0;
would_block: q->blocking = sop; return sop->sem_flg & IPC_NOWAIT ? -EAGAIN : 1;}
static inline void wake_up_sem_queue_prepare(struct sem_queue *q, int error, struct wake_q_head *wake_q){ struct task_struct *sleeper;
sleeper = get_task_struct(q->sleeper);
/* see SEM_BARRIER_2 for purpose/pairing */ smp_store_release(&q->status, error);
wake_q_add_safe(wake_q, sleeper);}
static void unlink_queue(struct sem_array *sma, struct sem_queue *q){ list_del(&q->list); if (q->nsops > 1) sma->complex_count--;}
/** check_restart(sma, q) * @sma: semaphore array * @q: the operation that just completed * * update_queue is O(N^2) when it restarts scanning the whole queue of * waiting operations. Therefore this function checks if the restart is * really necessary. It is called after a previously waiting operation * modified the array. * Note that wait-for-zero operations are handled without restart. */static inline int check_restart(struct sem_array *sma, struct sem_queue *q){ /* pending complex alter operations are too difficult to analyse */ if (!list_empty(&sma->pending_alter)) return 1;
/* we were a sleeping complex operation. Too difficult */ if (q->nsops > 1) return 1;
/* It is impossible that someone waits for the new value: * - complex operations always restart. * - wait-for-zero are handled separately. * - q is a previously sleeping simple operation that * altered the array. It must be a decrement, because * simple increments never sleep. * - If there are older (higher priority) decrements * in the queue, then they have observed the original * semval value and couldn't proceed. The operation * decremented to value - thus they won't proceed either. */ return 0;}
/** * wake_const_ops - wake up non-alter tasks * @sma: semaphore array. * @semnum: semaphore that was modified. * @wake_q: lockless wake-queue head. * * wake_const_ops must be called after a semaphore in a semaphore array * was set to 0. If complex const operations are pending, wake_const_ops must * be called with semnum = -1, as well as with the number of each modified * semaphore. * The tasks that must be woken up are added to @wake_q. The return code * is stored in q->pid. * The function returns 1 if at least one operation was completed successfully. */static int wake_const_ops(struct sem_array *sma, int semnum, struct wake_q_head *wake_q){ struct sem_queue *q, *tmp; struct list_head *pending_list; int semop_completed = 0;
if (semnum == -1) pending_list = &sma->pending_const; else pending_list = &sma->sems[semnum].pending_const;
list_for_each_entry_safe(q, tmp, pending_list, list) { int error = perform_atomic_semop(sma, q);
if (error > 0) continue; /* operation completed, remove from queue & wakeup */ unlink_queue(sma, q);
wake_up_sem_queue_prepare(q, error, wake_q); if (error == 0) semop_completed = 1; }
return semop_completed;}
/** * do_smart_wakeup_zero - wakeup all wait for zero tasks * @sma: semaphore array * @sops: operations that were performed * @nsops: number of operations * @wake_q: lockless wake-queue head * * Checks all required queue for wait-for-zero operations, based * on the actual changes that were performed on the semaphore array. * The function returns 1 if at least one operation was completed successfully. */static int do_smart_wakeup_zero(struct sem_array *sma, struct sembuf *sops, int nsops, struct wake_q_head *wake_q){ int i; int semop_completed = 0; int got_zero = 0;
/* first: the per-semaphore queues, if known */ if (sops) { for (i = 0; i < nsops; i++) { int num = sops[i].sem_num;
if (sma->sems[num].semval == 0) { got_zero = 1; semop_completed |= wake_const_ops(sma, num, wake_q); } } } else { /* * No sops means modified semaphores not known. * Assume all were changed. */ for (i = 0; i < sma->sem_nsems; i++) { if (sma->sems[i].semval == 0) { got_zero = 1; semop_completed |= wake_const_ops(sma, i, wake_q); } } } /* * If one of the modified semaphores got 0, * then check the global queue, too. */ if (got_zero) semop_completed |= wake_const_ops(sma, -1, wake_q);
return semop_completed;}
/** * update_queue - look for tasks that can be completed. * @sma: semaphore array. * @semnum: semaphore that was modified. * @wake_q: lockless wake-queue head. * * update_queue must be called after a semaphore in a semaphore array * was modified. If multiple semaphores were modified, update_queue must * be called with semnum = -1, as well as with the number of each modified * semaphore. * The tasks that must be woken up are added to @wake_q. The return code * is stored in q->pid. * The function internally checks if const operations can now succeed. * * The function return 1 if at least one semop was completed successfully. */static int update_queue(struct sem_array *sma, int semnum, struct wake_q_head *wake_q){ struct sem_queue *q, *tmp; struct list_head *pending_list; int semop_completed = 0;
if (semnum == -1) pending_list = &sma->pending_alter; else pending_list = &sma->sems[semnum].pending_alter;
again: list_for_each_entry_safe(q, tmp, pending_list, list) { int error, restart;
/* If we are scanning the single sop, per-semaphore list of * one semaphore and that semaphore is 0, then it is not * necessary to scan further: simple increments * that affect only one entry succeed immediately and cannot * be in the per semaphore pending queue, and decrements * cannot be successful if the value is already 0. */ if (semnum != -1 && sma->sems[semnum].semval == 0) break;
error = perform_atomic_semop(sma, q);
/* Does q->sleeper still need to sleep? */ if (error > 0) continue;
unlink_queue(sma, q);
if (error) { restart = 0; } else { semop_completed = 1; do_smart_wakeup_zero(sma, q->sops, q->nsops, wake_q); restart = check_restart(sma, q); }
wake_up_sem_queue_prepare(q, error, wake_q); if (restart) goto again; } return semop_completed;}
/** * set_semotime - set sem_otime * @sma: semaphore array * @sops: operations that modified the array, may be NULL * * sem_otime is replicated to avoid cache line trashing. * This function sets one instance to the current time. */static void set_semotime(struct sem_array *sma, struct sembuf *sops){ if (sops == NULL) { sma->sems[0].sem_otime = ktime_get_real_seconds(); } else { sma->sems[sops[0].sem_num].sem_otime = ktime_get_real_seconds(); }}
/** * do_smart_update - optimized update_queue * @sma: semaphore array * @sops: operations that were performed * @nsops: number of operations * @otime: force setting otime * @wake_q: lockless wake-queue head * * do_smart_update() does the required calls to update_queue and wakeup_zero, * based on the actual changes that were performed on the semaphore array. * Note that the function does not do the actual wake-up: the caller is * responsible for calling wake_up_q(). * It is safe to perform this call after dropping all locks. */static void do_smart_update(struct sem_array *sma, struct sembuf *sops, int nsops, int otime, struct wake_q_head *wake_q){ int i;
otime |= do_smart_wakeup_zero(sma, sops, nsops, wake_q);
if (!list_empty(&sma->pending_alter)) { /* semaphore array uses the global queue - just process it. */ otime |= update_queue(sma, -1, wake_q); } else { if (!sops) { /* * No sops, thus the modified semaphores are not * known. Check all. */ for (i = 0; i < sma->sem_nsems; i++) otime |= update_queue(sma, i, wake_q); } else { /* * Check the semaphores that were increased: * - No complex ops, thus all sleeping ops are * decrease. * - if we decreased the value, then any sleeping * semaphore ops won't be able to run: If the * previous value was too small, then the new * value will be too small, too. */ for (i = 0; i < nsops; i++) { if (sops[i].sem_op > 0) { otime |= update_queue(sma, sops[i].sem_num, wake_q); } } } } if (otime) set_semotime(sma, sops);}
/* * check_qop: Test if a queued operation sleeps on the semaphore semnum */static int check_qop(struct sem_array *sma, int semnum, struct sem_queue *q, bool count_zero){ struct sembuf *sop = q->blocking;
/* * Linux always (since 0.99.10) reported a task as sleeping on all * semaphores. This violates SUS, therefore it was changed to the * standard compliant behavior. * Give the administrators a chance to notice that an application * might misbehave because it relies on the Linux behavior. */ pr_info_once("semctl(GETNCNT/GETZCNT) is since 3.16 Single Unix Specification compliant.\n" "The task %s (%d) triggered the difference, watch for misbehavior.\n", current->comm, task_pid_nr(current));
if (sop->sem_num != semnum) return 0;
if (count_zero && sop->sem_op == 0) return 1; if (!count_zero && sop->sem_op < 0) return 1;
return 0;}
/* The following counts are associated to each semaphore: * semncnt number of tasks waiting on semval being nonzero * semzcnt number of tasks waiting on semval being zero * * Per definition, a task waits only on the semaphore of the first semop * that cannot proceed, even if additional operation would block, too. */static int count_semcnt(struct sem_array *sma, ushort semnum, bool count_zero){ struct list_head *l; struct sem_queue *q; int semcnt;
semcnt = 0; /* First: check the simple operations. They are easy to evaluate */ if (count_zero) l = &sma->sems[semnum].pending_const; else l = &sma->sems[semnum].pending_alter;
list_for_each_entry(q, l, list) { /* all task on a per-semaphore list sleep on exactly * that semaphore */ semcnt++; }
/* Then: check the complex operations. */ list_for_each_entry(q, &sma->pending_alter, list) { semcnt += check_qop(sma, semnum, q, count_zero); } if (count_zero) { list_for_each_entry(q, &sma->pending_const, list) { semcnt += check_qop(sma, semnum, q, count_zero); } } return semcnt;}
/* Free a semaphore set. freeary() is called with sem_ids.rwsem locked * as a writer and the spinlock for this semaphore set hold. sem_ids.rwsem * remains locked on exit. */static void freeary(struct ipc_namespace *ns, struct kern_ipc_perm *ipcp){ struct sem_undo *un, *tu; struct sem_queue *q, *tq; struct sem_array *sma = container_of(ipcp, struct sem_array, sem_perm); int i; DEFINE_WAKE_Q(wake_q);
/* Free the existing undo structures for this semaphore set. */ ipc_assert_locked_object(&sma->sem_perm); list_for_each_entry_safe(un, tu, &sma->list_id, list_id) { list_del(&un->list_id); spin_lock(&un->ulp->lock); un->semid = -1; list_del_rcu(&un->list_proc); spin_unlock(&un->ulp->lock); kvfree_rcu(un, rcu); }
/* Wake up all pending processes and let them fail with EIDRM. */ list_for_each_entry_safe(q, tq, &sma->pending_const, list) { unlink_queue(sma, q); wake_up_sem_queue_prepare(q, -EIDRM, &wake_q); }
list_for_each_entry_safe(q, tq, &sma->pending_alter, list) { unlink_queue(sma, q); wake_up_sem_queue_prepare(q, -EIDRM, &wake_q); } for (i = 0; i < sma->sem_nsems; i++) { struct sem *sem = &sma->sems[i]; list_for_each_entry_safe(q, tq, &sem->pending_const, list) { unlink_queue(sma, q); wake_up_sem_queue_prepare(q, -EIDRM, &wake_q); } list_for_each_entry_safe(q, tq, &sem->pending_alter, list) { unlink_queue(sma, q); wake_up_sem_queue_prepare(q, -EIDRM, &wake_q); } ipc_update_pid(&sem->sempid, NULL); }
/* Remove the semaphore set from the IDR */ sem_rmid(ns, sma); sem_unlock(sma, -1); rcu_read_unlock();
wake_up_q(&wake_q); ns->used_sems -= sma->sem_nsems; ipc_rcu_putref(&sma->sem_perm, sem_rcu_free);}
static unsigned long copy_semid_to_user(void __user *buf, struct semid64_ds *in, int version){ switch (version) { case IPC_64: return copy_to_user(buf, in, sizeof(*in)); case IPC_OLD: { struct semid_ds out;
memset(&out, 0, sizeof(out));
ipc64_perm_to_ipc_perm(&in->sem_perm, &out.sem_perm);
out.sem_otime = in->sem_otime; out.sem_ctime = in->sem_ctime; out.sem_nsems = in->sem_nsems;
return copy_to_user(buf, &out, sizeof(out)); } default: return -EINVAL; }}
static time64_t get_semotime(struct sem_array *sma){ int i; time64_t res;
res = sma->sems[0].sem_otime; for (i = 1; i < sma->sem_nsems; i++) { time64_t to = sma->sems[i].sem_otime;
if (to > res) res = to; } return res;}
static int semctl_stat(struct ipc_namespace *ns, int semid, int cmd, struct semid64_ds *semid64){ struct sem_array *sma; time64_t semotime; int err;
memset(semid64, 0, sizeof(*semid64));
rcu_read_lock(); if (cmd == SEM_STAT || cmd == SEM_STAT_ANY) { sma = sem_obtain_object(ns, semid); if (IS_ERR(sma)) { err = PTR_ERR(sma); goto out_unlock; } } else { /* IPC_STAT */ sma = sem_obtain_object_check(ns, semid); if (IS_ERR(sma)) { err = PTR_ERR(sma); goto out_unlock; } }
/* see comment for SHM_STAT_ANY */ if (cmd == SEM_STAT_ANY) audit_ipc_obj(&sma->sem_perm); else { err = -EACCES; if (ipcperms(ns, &sma->sem_perm, S_IRUGO)) goto out_unlock; }
err = security_sem_semctl(&sma->sem_perm, cmd); if (err) goto out_unlock;
ipc_lock_object(&sma->sem_perm);
if (!ipc_valid_object(&sma->sem_perm)) { ipc_unlock_object(&sma->sem_perm); err = -EIDRM; goto out_unlock; }
kernel_to_ipc64_perm(&sma->sem_perm, &semid64->sem_perm); semotime = get_semotime(sma); semid64->sem_otime = semotime; semid64->sem_ctime = sma->sem_ctime;#ifndef CONFIG_64BIT semid64->sem_otime_high = semotime >> 32; semid64->sem_ctime_high = sma->sem_ctime >> 32;#endif semid64->sem_nsems = sma->sem_nsems;
if (cmd == IPC_STAT) { /* * As defined in SUS: * Return 0 on success */ err = 0; } else { /* * SEM_STAT and SEM_STAT_ANY (both Linux specific) * Return the full id, including the sequence number */ err = sma->sem_perm.id; } ipc_unlock_object(&sma->sem_perm);out_unlock: rcu_read_unlock(); return err;}
static int semctl_info(struct ipc_namespace *ns, int semid, int cmd, void __user *p){ struct seminfo seminfo; int max_idx; int err;
err = security_sem_semctl(NULL, cmd); if (err) return err;
memset(&seminfo, 0, sizeof(seminfo)); seminfo.semmni = ns->sc_semmni; seminfo.semmns = ns->sc_semmns; seminfo.semmsl = ns->sc_semmsl; seminfo.semopm = ns->sc_semopm; seminfo.semvmx = SEMVMX; seminfo.semmnu = SEMMNU; seminfo.semmap = SEMMAP; seminfo.semume = SEMUME; down_read(&sem_ids(ns).rwsem); if (cmd == SEM_INFO) { seminfo.semusz = sem_ids(ns).in_use; seminfo.semaem = ns->used_sems; } else { seminfo.semusz = SEMUSZ; seminfo.semaem = SEMAEM; } max_idx = ipc_get_maxidx(&sem_ids(ns)); up_read(&sem_ids(ns).rwsem); if (copy_to_user(p, &seminfo, sizeof(struct seminfo))) return -EFAULT; return (max_idx < 0) ? 0 : max_idx;}
static int semctl_setval(struct ipc_namespace *ns, int semid, int semnum, int val){ struct sem_undo *un; struct sem_array *sma; struct sem *curr; int err; DEFINE_WAKE_Q(wake_q);
if (val > SEMVMX || val < 0) return -ERANGE;
rcu_read_lock(); sma = sem_obtain_object_check(ns, semid); if (IS_ERR(sma)) { rcu_read_unlock(); return PTR_ERR(sma); }
if (semnum < 0 || semnum >= sma->sem_nsems) { rcu_read_unlock(); return -EINVAL; }
if (ipcperms(ns, &sma->sem_perm, S_IWUGO)) { rcu_read_unlock(); return -EACCES; }
err = security_sem_semctl(&sma->sem_perm, SETVAL); if (err) { rcu_read_unlock(); return -EACCES; }
sem_lock(sma, NULL, -1);
if (!ipc_valid_object(&sma->sem_perm)) { sem_unlock(sma, -1); rcu_read_unlock(); return -EIDRM; }
semnum = array_index_nospec(semnum, sma->sem_nsems); curr = &sma->sems[semnum];
ipc_assert_locked_object(&sma->sem_perm); list_for_each_entry(un, &sma->list_id, list_id) un->semadj[semnum] = 0;
curr->semval = val; ipc_update_pid(&curr->sempid, task_tgid(current)); sma->sem_ctime = ktime_get_real_seconds(); /* maybe some queued-up processes were waiting for this */ do_smart_update(sma, NULL, 0, 0, &wake_q); sem_unlock(sma, -1); rcu_read_unlock(); wake_up_q(&wake_q); return 0;}
static int semctl_main(struct ipc_namespace *ns, int semid, int semnum, int cmd, void __user *p){ struct sem_array *sma; struct sem *curr; int err, nsems; ushort fast_sem_io[SEMMSL_FAST]; ushort *sem_io = fast_sem_io; DEFINE_WAKE_Q(wake_q);
rcu_read_lock(); sma = sem_obtain_object_check(ns, semid); if (IS_ERR(sma)) { rcu_read_unlock(); return PTR_ERR(sma); }
nsems = sma->sem_nsems;
err = -EACCES; if (ipcperms(ns, &sma->sem_perm, cmd == SETALL ? S_IWUGO : S_IRUGO)) goto out_rcu_wakeup;
err = security_sem_semctl(&sma->sem_perm, cmd); if (err) goto out_rcu_wakeup;
switch (cmd) { case GETALL: { ushort __user *array = p; int i;
sem_lock(sma, NULL, -1); if (!ipc_valid_object(&sma->sem_perm)) { err = -EIDRM; goto out_unlock; } if (nsems > SEMMSL_FAST) { if (!ipc_rcu_getref(&sma->sem_perm)) { err = -EIDRM; goto out_unlock; } sem_unlock(sma, -1); rcu_read_unlock(); sem_io = kvmalloc_array(nsems, sizeof(ushort), GFP_KERNEL); if (sem_io == NULL) { ipc_rcu_putref(&sma->sem_perm, sem_rcu_free); return -ENOMEM; }
rcu_read_lock(); sem_lock_and_putref(sma); if (!ipc_valid_object(&sma->sem_perm)) { err = -EIDRM; goto out_unlock; } } for (i = 0; i < sma->sem_nsems; i++) sem_io[i] = sma->sems[i].semval; sem_unlock(sma, -1); rcu_read_unlock(); err = 0; if (copy_to_user(array, sem_io, nsems*sizeof(ushort))) err = -EFAULT; goto out_free; } case SETALL: { int i; struct sem_undo *un;
if (!ipc_rcu_getref(&sma->sem_perm)) { err = -EIDRM; goto out_rcu_wakeup; } rcu_read_unlock();
if (nsems > SEMMSL_FAST) { sem_io = kvmalloc_array(nsems, sizeof(ushort), GFP_KERNEL); if (sem_io == NULL) { ipc_rcu_putref(&sma->sem_perm, sem_rcu_free); return -ENOMEM; } }
if (copy_from_user(sem_io, p, nsems*sizeof(ushort))) { ipc_rcu_putref(&sma->sem_perm, sem_rcu_free); err = -EFAULT; goto out_free; }
for (i = 0; i < nsems; i++) { if (sem_io[i] > SEMVMX) { ipc_rcu_putref(&sma->sem_perm, sem_rcu_free); err = -ERANGE; goto out_free; } } rcu_read_lock(); sem_lock_and_putref(sma); if (!ipc_valid_object(&sma->sem_perm)) { err = -EIDRM; goto out_unlock; }
for (i = 0; i < nsems; i++) { sma->sems[i].semval = sem_io[i]; ipc_update_pid(&sma->sems[i].sempid, task_tgid(current)); }
ipc_assert_locked_object(&sma->sem_perm); list_for_each_entry(un, &sma->list_id, list_id) { for (i = 0; i < nsems; i++) un->semadj[i] = 0; } sma->sem_ctime = ktime_get_real_seconds(); /* maybe some queued-up processes were waiting for this */ do_smart_update(sma, NULL, 0, 0, &wake_q); err = 0; goto out_unlock; } /* GETVAL, GETPID, GETNCTN, GETZCNT: fall-through */ } err = -EINVAL; if (semnum < 0 || semnum >= nsems) goto out_rcu_wakeup;
sem_lock(sma, NULL, -1); if (!ipc_valid_object(&sma->sem_perm)) { err = -EIDRM; goto out_unlock; }
semnum = array_index_nospec(semnum, nsems); curr = &sma->sems[semnum];
switch (cmd) { case GETVAL: err = curr->semval; goto out_unlock; case GETPID: err = pid_vnr(curr->sempid); goto out_unlock; case GETNCNT: err = count_semcnt(sma, semnum, 0); goto out_unlock; case GETZCNT: err = count_semcnt(sma, semnum, 1); goto out_unlock; }
out_unlock: sem_unlock(sma, -1);out_rcu_wakeup: rcu_read_unlock(); wake_up_q(&wake_q);out_free: if (sem_io != fast_sem_io) kvfree(sem_io); return err;}
static inline unsigned longcopy_semid_from_user(struct semid64_ds *out, void __user *buf, int version){ switch (version) { case IPC_64: if (copy_from_user(out, buf, sizeof(*out))) return -EFAULT; return 0; case IPC_OLD: { struct semid_ds tbuf_old;
if (copy_from_user(&tbuf_old, buf, sizeof(tbuf_old))) return -EFAULT;
out->sem_perm.uid = tbuf_old.sem_perm.uid; out->sem_perm.gid = tbuf_old.sem_perm.gid; out->sem_perm.mode = tbuf_old.sem_perm.mode;
return 0; } default: return -EINVAL; }}
/* * This function handles some semctl commands which require the rwsem * to be held in write mode. * NOTE: no locks must be held, the rwsem is taken inside this function. */static int semctl_down(struct ipc_namespace *ns, int semid, int cmd, struct semid64_ds *semid64){ struct sem_array *sma; int err; struct kern_ipc_perm *ipcp;
down_write(&sem_ids(ns).rwsem); rcu_read_lock();
ipcp = ipcctl_obtain_check(ns, &sem_ids(ns), semid, cmd, &semid64->sem_perm, 0); if (IS_ERR(ipcp)) { err = PTR_ERR(ipcp); goto out_unlock1; }
sma = container_of(ipcp, struct sem_array, sem_perm);
err = security_sem_semctl(&sma->sem_perm, cmd); if (err) goto out_unlock1;
switch (cmd) { case IPC_RMID: sem_lock(sma, NULL, -1); /* freeary unlocks the ipc object and rcu */ freeary(ns, ipcp); goto out_up; case IPC_SET: sem_lock(sma, NULL, -1); err = ipc_update_perm(&semid64->sem_perm, ipcp); if (err) goto out_unlock0; sma->sem_ctime = ktime_get_real_seconds(); break; default: err = -EINVAL; goto out_unlock1; }
out_unlock0: sem_unlock(sma, -1);out_unlock1: rcu_read_unlock();out_up: up_write(&sem_ids(ns).rwsem); return err;}
static long ksys_semctl(int semid, int semnum, int cmd, unsigned long arg, int version){ struct ipc_namespace *ns; void __user *p = (void __user *)arg; struct semid64_ds semid64; int err;
if (semid < 0) return -EINVAL;
ns = current->nsproxy->ipc_ns;
switch (cmd) { case IPC_INFO: case SEM_INFO: return semctl_info(ns, semid, cmd, p); case IPC_STAT: case SEM_STAT: case SEM_STAT_ANY: err = semctl_stat(ns, semid, cmd, &semid64); if (err < 0) return err; if (copy_semid_to_user(p, &semid64, version)) err = -EFAULT; return err; case GETALL: case GETVAL: case GETPID: case GETNCNT: case GETZCNT: case SETALL: return semctl_main(ns, semid, semnum, cmd, p); case SETVAL: { int val;#if defined(CONFIG_64BIT) && defined(__BIG_ENDIAN) /* big-endian 64bit */ val = arg >> 32;#else /* 32bit or little-endian 64bit */ val = arg;#endif return semctl_setval(ns, semid, semnum, val); } case IPC_SET: if (copy_semid_from_user(&semid64, p, version)) return -EFAULT; fallthrough; case IPC_RMID: return semctl_down(ns, semid, cmd, &semid64); default: return -EINVAL; }}
SYSCALL_DEFINE4(semctl, int, semid, int, semnum, int, cmd, unsigned long, arg){ return ksys_semctl(semid, semnum, cmd, arg, IPC_64);}
#ifdef CONFIG_ARCH_WANT_IPC_PARSE_VERSIONlong ksys_old_semctl(int semid, int semnum, int cmd, unsigned long arg){ int version = ipc_parse_version(&cmd);
return ksys_semctl(semid, semnum, cmd, arg, version);}
SYSCALL_DEFINE4(old_semctl, int, semid, int, semnum, int, cmd, unsigned long, arg){ return ksys_old_semctl(semid, semnum, cmd, arg);}#endif
#ifdef CONFIG_COMPAT
struct compat_semid_ds { struct compat_ipc_perm sem_perm; old_time32_t sem_otime; old_time32_t sem_ctime; compat_uptr_t sem_base; compat_uptr_t sem_pending; compat_uptr_t sem_pending_last; compat_uptr_t undo; unsigned short sem_nsems;};
static int copy_compat_semid_from_user(struct semid64_ds *out, void __user *buf, int version){ memset(out, 0, sizeof(*out)); if (version == IPC_64) { struct compat_semid64_ds __user *p = buf; return get_compat_ipc64_perm(&out->sem_perm, &p->sem_perm); } else { struct compat_semid_ds __user *p = buf; return get_compat_ipc_perm(&out->sem_perm, &p->sem_perm); }}
static int copy_compat_semid_to_user(void __user *buf, struct semid64_ds *in, int version){ if (version == IPC_64) { struct compat_semid64_ds v; memset(&v, 0, sizeof(v)); to_compat_ipc64_perm(&v.sem_perm, &in->sem_perm); v.sem_otime = lower_32_bits(in->sem_otime); v.sem_otime_high = upper_32_bits(in->sem_otime); v.sem_ctime = lower_32_bits(in->sem_ctime); v.sem_ctime_high = upper_32_bits(in->sem_ctime); v.sem_nsems = in->sem_nsems; return copy_to_user(buf, &v, sizeof(v)); } else { struct compat_semid_ds v; memset(&v, 0, sizeof(v)); to_compat_ipc_perm(&v.sem_perm, &in->sem_perm); v.sem_otime = in->sem_otime; v.sem_ctime = in->sem_ctime; v.sem_nsems = in->sem_nsems; return copy_to_user(buf, &v, sizeof(v)); }}
static long compat_ksys_semctl(int semid, int semnum, int cmd, int arg, int version){ void __user *p = compat_ptr(arg); struct ipc_namespace *ns; struct semid64_ds semid64; int err;
ns = current->nsproxy->ipc_ns;
if (semid < 0) return -EINVAL;
switch (cmd & (~IPC_64)) { case IPC_INFO: case SEM_INFO: return semctl_info(ns, semid, cmd, p); case IPC_STAT: case SEM_STAT: case SEM_STAT_ANY: err = semctl_stat(ns, semid, cmd, &semid64); if (err < 0) return err; if (copy_compat_semid_to_user(p, &semid64, version)) err = -EFAULT; return err; case GETVAL: case GETPID: case GETNCNT: case GETZCNT: case GETALL: case SETALL: return semctl_main(ns, semid, semnum, cmd, p); case SETVAL: return semctl_setval(ns, semid, semnum, arg); case IPC_SET: if (copy_compat_semid_from_user(&semid64, p, version)) return -EFAULT; fallthrough; case IPC_RMID: return semctl_down(ns, semid, cmd, &semid64); default: return -EINVAL; }}
COMPAT_SYSCALL_DEFINE4(semctl, int, semid, int, semnum, int, cmd, int, arg){ return compat_ksys_semctl(semid, semnum, cmd, arg, IPC_64);}
#ifdef CONFIG_ARCH_WANT_COMPAT_IPC_PARSE_VERSIONlong compat_ksys_old_semctl(int semid, int semnum, int cmd, int arg){ int version = compat_ipc_parse_version(&cmd);
return compat_ksys_semctl(semid, semnum, cmd, arg, version);}
COMPAT_SYSCALL_DEFINE4(old_semctl, int, semid, int, semnum, int, cmd, int, arg){ return compat_ksys_old_semctl(semid, semnum, cmd, arg);}#endif#endif
/* If the task doesn't already have a undo_list, then allocate one * here. We guarantee there is only one thread using this undo list, * and current is THE ONE * * If this allocation and assignment succeeds, but later * portions of this code fail, there is no need to free the sem_undo_list. * Just let it stay associated with the task, and it'll be freed later * at exit time. * * This can block, so callers must hold no locks. */static inline int get_undo_list(struct sem_undo_list **undo_listp){ struct sem_undo_list *undo_list;
undo_list = current->sysvsem.undo_list; if (!undo_list) { undo_list = kzalloc_obj(*undo_list, GFP_KERNEL_ACCOUNT); if (undo_list == NULL) return -ENOMEM; spin_lock_init(&undo_list->lock); refcount_set(&undo_list->refcnt, 1); INIT_LIST_HEAD(&undo_list->list_proc);
current->sysvsem.undo_list = undo_list; } *undo_listp = undo_list; return 0;}
static struct sem_undo *__lookup_undo(struct sem_undo_list *ulp, int semid){ struct sem_undo *un;
list_for_each_entry_rcu(un, &ulp->list_proc, list_proc, spin_is_locked(&ulp->lock)) { if (un->semid == semid) return un; } return NULL;}
static struct sem_undo *lookup_undo(struct sem_undo_list *ulp, int semid){ struct sem_undo *un;
assert_spin_locked(&ulp->lock);
un = __lookup_undo(ulp, semid); if (un) { list_del_rcu(&un->list_proc); list_add_rcu(&un->list_proc, &ulp->list_proc); } return un;}
/** * find_alloc_undo - lookup (and if not present create) undo array * @ns: namespace * @semid: semaphore array id * * The function looks up (and if not present creates) the undo structure. * The size of the undo structure depends on the size of the semaphore * array, thus the alloc path is not that straightforward. * Lifetime-rules: sem_undo is rcu-protected, on success, the function * performs a rcu_read_lock(). */static struct sem_undo *find_alloc_undo(struct ipc_namespace *ns, int semid){ struct sem_array *sma; struct sem_undo_list *ulp; struct sem_undo *un, *new; int nsems, error;
error = get_undo_list(&ulp); if (error) return ERR_PTR(error);
rcu_read_lock(); spin_lock(&ulp->lock); un = lookup_undo(ulp, semid); spin_unlock(&ulp->lock); if (likely(un != NULL)) goto out;
/* no undo structure around - allocate one. */ /* step 1: figure out the size of the semaphore array */ sma = sem_obtain_object_check(ns, semid); if (IS_ERR(sma)) { rcu_read_unlock(); return ERR_CAST(sma); }
nsems = sma->sem_nsems; if (!ipc_rcu_getref(&sma->sem_perm)) { rcu_read_unlock(); un = ERR_PTR(-EIDRM); goto out; } rcu_read_unlock();
/* step 2: allocate new undo structure */ new = kvzalloc_flex(*new, semadj, nsems, GFP_KERNEL_ACCOUNT); if (!new) { ipc_rcu_putref(&sma->sem_perm, sem_rcu_free); return ERR_PTR(-ENOMEM); }
/* step 3: Acquire the lock on semaphore array */ rcu_read_lock(); sem_lock_and_putref(sma); if (!ipc_valid_object(&sma->sem_perm)) { sem_unlock(sma, -1); rcu_read_unlock(); kvfree(new); un = ERR_PTR(-EIDRM); goto out; } spin_lock(&ulp->lock);
/* * step 4: check for races: did someone else allocate the undo struct? */ un = lookup_undo(ulp, semid); if (un) { spin_unlock(&ulp->lock); kvfree(new); goto success; } /* step 5: initialize & link new undo structure */ new->ulp = ulp; new->semid = semid; assert_spin_locked(&ulp->lock); list_add_rcu(&new->list_proc, &ulp->list_proc); ipc_assert_locked_object(&sma->sem_perm); list_add(&new->list_id, &sma->list_id); un = new; spin_unlock(&ulp->lock);success: sem_unlock(sma, -1);out: return un;}
long __do_semtimedop(int semid, struct sembuf *sops, unsigned int nsops, const struct timespec64 *timeout, struct ipc_namespace *ns){ int error = -EINVAL; struct sem_array *sma; struct sembuf *sop; struct sem_undo *un; int max, locknum; bool undos = false, alter = false, dupsop = false; struct sem_queue queue; unsigned long dup = 0; ktime_t expires, *exp = NULL; bool timed_out = false;
if (nsops < 1 || semid < 0) return -EINVAL; if (nsops > ns->sc_semopm) return -E2BIG;
if (timeout) { if (!timespec64_valid(timeout)) return -EINVAL; expires = ktime_add_safe(ktime_get(), timespec64_to_ktime(*timeout)); exp = &expires; }
max = 0; for (sop = sops; sop < sops + nsops; sop++) { unsigned long mask = 1ULL << ((sop->sem_num) % BITS_PER_LONG);
if (sop->sem_num >= max) max = sop->sem_num; if (sop->sem_flg & SEM_UNDO) undos = true; if (dup & mask) { /* * There was a previous alter access that appears * to have accessed the same semaphore, thus use * the dupsop logic. "appears", because the detection * can only check % BITS_PER_LONG. */ dupsop = true; } if (sop->sem_op != 0) { alter = true; dup |= mask; } }
if (undos) { /* On success, find_alloc_undo takes the rcu_read_lock */ un = find_alloc_undo(ns, semid); if (IS_ERR(un)) { error = PTR_ERR(un); goto out; } } else { un = NULL; rcu_read_lock(); }
sma = sem_obtain_object_check(ns, semid); if (IS_ERR(sma)) { rcu_read_unlock(); error = PTR_ERR(sma); goto out; }
error = -EFBIG; if (max >= sma->sem_nsems) { rcu_read_unlock(); goto out; }
error = -EACCES; if (ipcperms(ns, &sma->sem_perm, alter ? S_IWUGO : S_IRUGO)) { rcu_read_unlock(); goto out; }
error = security_sem_semop(&sma->sem_perm, sops, nsops, alter); if (error) { rcu_read_unlock(); goto out; }
error = -EIDRM; locknum = sem_lock(sma, sops, nsops); /* * We eventually might perform the following check in a lockless * fashion, considering ipc_valid_object() locking constraints. * If nsops == 1 and there is no contention for sem_perm.lock, then * only a per-semaphore lock is held and it's OK to proceed with the * check below. More details on the fine grained locking scheme * entangled here and why it's RMID race safe on comments at sem_lock() */ if (!ipc_valid_object(&sma->sem_perm)) goto out_unlock; /* * semid identifiers are not unique - find_alloc_undo may have * allocated an undo structure, it was invalidated by an RMID * and now a new array with received the same id. Check and fail. * This case can be detected checking un->semid. The existence of * "un" itself is guaranteed by rcu. */ if (un && un->semid == -1) goto out_unlock;
queue.sops = sops; queue.nsops = nsops; queue.undo = un; queue.pid = task_tgid(current); queue.alter = alter; queue.dupsop = dupsop;
error = perform_atomic_semop(sma, &queue); if (error == 0) { /* non-blocking successful path */ DEFINE_WAKE_Q(wake_q);
/* * If the operation was successful, then do * the required updates. */ if (alter) do_smart_update(sma, sops, nsops, 1, &wake_q); else set_semotime(sma, sops);
sem_unlock(sma, locknum); rcu_read_unlock(); wake_up_q(&wake_q);
goto out; } if (error < 0) /* non-blocking error path */ goto out_unlock;
/* * We need to sleep on this operation, so we put the current * task into the pending queue and go to sleep. */ if (nsops == 1) { struct sem *curr; int idx = array_index_nospec(sops->sem_num, sma->sem_nsems); curr = &sma->sems[idx];
if (alter) { if (sma->complex_count) { list_add_tail(&queue.list, &sma->pending_alter); } else {
list_add_tail(&queue.list, &curr->pending_alter); } } else { list_add_tail(&queue.list, &curr->pending_const); } } else { if (!sma->complex_count) merge_queues(sma);
if (alter) list_add_tail(&queue.list, &sma->pending_alter); else list_add_tail(&queue.list, &sma->pending_const);
sma->complex_count++; }
do { /* memory ordering ensured by the lock in sem_lock() */ WRITE_ONCE(queue.status, -EINTR); queue.sleeper = current;
/* memory ordering is ensured by the lock in sem_lock() */ __set_current_state(TASK_INTERRUPTIBLE); sem_unlock(sma, locknum); rcu_read_unlock();
timed_out = !schedule_hrtimeout_range(exp, current->timer_slack_ns, HRTIMER_MODE_ABS);
/* * fastpath: the semop has completed, either successfully or * not, from the syscall pov, is quite irrelevant to us at this * point; we're done. * * We _do_ care, nonetheless, about being awoken by a signal or * spuriously. The queue.status is checked again in the * slowpath (aka after taking sem_lock), such that we can detect * scenarios where we were awakened externally, during the * window between wake_q_add() and wake_up_q(). */ rcu_read_lock(); error = READ_ONCE(queue.status); if (error != -EINTR) { /* see SEM_BARRIER_2 for purpose/pairing */ smp_acquire__after_ctrl_dep(); rcu_read_unlock(); goto out; }
locknum = sem_lock(sma, sops, nsops);
if (!ipc_valid_object(&sma->sem_perm)) goto out_unlock;
/* * No necessity for any barrier: We are protect by sem_lock() */ error = READ_ONCE(queue.status);
/* * If queue.status != -EINTR we are woken up by another process. * Leave without unlink_queue(), but with sem_unlock(). */ if (error != -EINTR) goto out_unlock;
/* * If an interrupt occurred we have to clean up the queue. */ if (timed_out) error = -EAGAIN; } while (error == -EINTR && !signal_pending(current)); /* spurious */
unlink_queue(sma, &queue);
out_unlock: sem_unlock(sma, locknum); rcu_read_unlock();out: return error;}
static long do_semtimedop(int semid, struct sembuf __user *tsops, unsigned int nsops, const struct timespec64 *timeout){ struct sembuf fast_sops[SEMOPM_FAST]; struct sembuf *sops = fast_sops; struct ipc_namespace *ns; int ret;
ns = current->nsproxy->ipc_ns; if (nsops > ns->sc_semopm) return -E2BIG; if (nsops < 1) return -EINVAL;
if (nsops > SEMOPM_FAST) { sops = kvmalloc_objs(*sops, nsops); if (sops == NULL) return -ENOMEM; }
if (copy_from_user(sops, tsops, nsops * sizeof(*tsops))) { ret = -EFAULT; goto out_free; }
ret = __do_semtimedop(semid, sops, nsops, timeout, ns);
out_free: if (sops != fast_sops) kvfree(sops);
return ret;}
long ksys_semtimedop(int semid, struct sembuf __user *tsops, unsigned int nsops, const struct __kernel_timespec __user *timeout){ if (timeout) { struct timespec64 ts; if (get_timespec64(&ts, timeout)) return -EFAULT; return do_semtimedop(semid, tsops, nsops, &ts); } return do_semtimedop(semid, tsops, nsops, NULL);}
SYSCALL_DEFINE4(semtimedop, int, semid, struct sembuf __user *, tsops, unsigned int, nsops, const struct __kernel_timespec __user *, timeout){ return ksys_semtimedop(semid, tsops, nsops, timeout);}
#ifdef CONFIG_COMPAT_32BIT_TIMElong compat_ksys_semtimedop(int semid, struct sembuf __user *tsems, unsigned int nsops, const struct old_timespec32 __user *timeout){ if (timeout) { struct timespec64 ts; if (get_old_timespec32(&ts, timeout)) return -EFAULT; return do_semtimedop(semid, tsems, nsops, &ts); } return do_semtimedop(semid, tsems, nsops, NULL);}
SYSCALL_DEFINE4(semtimedop_time32, int, semid, struct sembuf __user *, tsems, unsigned int, nsops, const struct old_timespec32 __user *, timeout){ return compat_ksys_semtimedop(semid, tsems, nsops, timeout);}#endif
SYSCALL_DEFINE3(semop, int, semid, struct sembuf __user *, tsops, unsigned int, nsops){ return do_semtimedop(semid, tsops, nsops, NULL);}
/* If CLONE_SYSVSEM is set, establish sharing of SEM_UNDO state between * parent and child tasks. */
int copy_semundo(u64 clone_flags, struct task_struct *tsk){ struct sem_undo_list *undo_list; int error;
if (clone_flags & CLONE_SYSVSEM) { error = get_undo_list(&undo_list); if (error) return error; refcount_inc(&undo_list->refcnt); tsk->sysvsem.undo_list = undo_list; } else tsk->sysvsem.undo_list = NULL;
return 0;}
/* * add semadj values to semaphores, free undo structures. * undo structures are not freed when semaphore arrays are destroyed * so some of them may be out of date. * IMPLEMENTATION NOTE: There is some confusion over whether the * set of adjustments that needs to be done should be done in an atomic * manner or not. That is, if we are attempting to decrement the semval * should we queue up and wait until we can do so legally? * The original implementation attempted to do this (queue and wait). * The current implementation does not do so. The POSIX standard * and SVID should be consulted to determine what behavior is mandated. */void exit_sem(struct task_struct *tsk){ struct sem_undo_list *ulp;
ulp = tsk->sysvsem.undo_list; if (!ulp) return; tsk->sysvsem.undo_list = NULL;
if (!refcount_dec_and_test(&ulp->refcnt)) return;
for (;;) { struct sem_array *sma; struct sem_undo *un; int semid, i; DEFINE_WAKE_Q(wake_q);
cond_resched();
rcu_read_lock(); un = list_entry_rcu(ulp->list_proc.next, struct sem_undo, list_proc); if (&un->list_proc == &ulp->list_proc) { /* * We must wait for freeary() before freeing this ulp, * in case we raced with last sem_undo. There is a small * possibility where we exit while freeary() didn't * finish unlocking sem_undo_list. */ spin_lock(&ulp->lock); spin_unlock(&ulp->lock); rcu_read_unlock(); break; } spin_lock(&ulp->lock); semid = un->semid; spin_unlock(&ulp->lock);
/* exit_sem raced with IPC_RMID, nothing to do */ if (semid == -1) { rcu_read_unlock(); continue; }
sma = sem_obtain_object_check(tsk->nsproxy->ipc_ns, semid); /* exit_sem raced with IPC_RMID, nothing to do */ if (IS_ERR(sma)) { rcu_read_unlock(); continue; }
sem_lock(sma, NULL, -1); /* exit_sem raced with IPC_RMID, nothing to do */ if (!ipc_valid_object(&sma->sem_perm)) { sem_unlock(sma, -1); rcu_read_unlock(); continue; } un = __lookup_undo(ulp, semid); if (un == NULL) { /* exit_sem raced with IPC_RMID+semget() that created * exactly the same semid. Nothing to do. */ sem_unlock(sma, -1); rcu_read_unlock(); continue; }
/* remove un from the linked lists */ ipc_assert_locked_object(&sma->sem_perm); list_del(&un->list_id);
spin_lock(&ulp->lock); list_del_rcu(&un->list_proc); spin_unlock(&ulp->lock);
/* perform adjustments registered in un */ for (i = 0; i < sma->sem_nsems; i++) { struct sem *semaphore = &sma->sems[i]; if (un->semadj[i]) { semaphore->semval += un->semadj[i]; /* * Range checks of the new semaphore value, * not defined by sus: * - Some unices ignore the undo entirely * (e.g. HP UX 11i 11.22, Tru64 V5.1) * - some cap the value (e.g. FreeBSD caps * at 0, but doesn't enforce SEMVMX) * * Linux caps the semaphore value, both at 0 * and at SEMVMX. * * Manfred <manfred@colorfullife.com> */ if (semaphore->semval < 0) semaphore->semval = 0; if (semaphore->semval > SEMVMX) semaphore->semval = SEMVMX; ipc_update_pid(&semaphore->sempid, task_tgid(current)); } } /* maybe some queued-up processes were waiting for this */ do_smart_update(sma, NULL, 0, 1, &wake_q); sem_unlock(sma, -1); rcu_read_unlock(); wake_up_q(&wake_q);
kvfree_rcu(un, rcu); } kfree(ulp);}
#ifdef CONFIG_PROC_FSstatic int sysvipc_sem_proc_show(struct seq_file *s, void *it){ struct user_namespace *user_ns = seq_user_ns(s); struct kern_ipc_perm *ipcp = it; struct sem_array *sma = container_of(ipcp, struct sem_array, sem_perm); time64_t sem_otime;
/* * The proc interface isn't aware of sem_lock(), it calls * ipc_lock_object(), i.e. spin_lock(&sma->sem_perm.lock). * (in sysvipc_find_ipc) * In order to stay compatible with sem_lock(), we must * enter / leave complex_mode. */ complexmode_enter(sma);
sem_otime = get_semotime(sma);
seq_printf(s, "%10d %10d %4o %10u %5u %5u %5u %5u %10llu %10llu\n", sma->sem_perm.key, sma->sem_perm.id, sma->sem_perm.mode, sma->sem_nsems, from_kuid_munged(user_ns, sma->sem_perm.uid), from_kgid_munged(user_ns, sma->sem_perm.gid), from_kuid_munged(user_ns, sma->sem_perm.cuid), from_kgid_munged(user_ns, sma->sem_perm.cgid), sem_otime, sma->sem_ctime);
complexmode_tryleave(sma);
return 0;}#endif