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ipc: introduce ipc_valid_object() helper to sort out IPC_RMID races 

After the locking semantics for the SysV IPC API got improved, a couple
of IPC_RMID race windows were opened because we ended up dropping the
'kern_ipc_perm.deleted' check performed way down in ipc_lock().  The
spotted races got sorted out by re-introducing the old test within the
racy critical sections.

This patch introduces ipc_valid_object() to consolidate the way we cope
with IPC_RMID races by using the same abstraction across the API
implementation.

Signed-off-by: Rafael Aquini <aquini@redhat.com>
Acked-by: Rik van Riel <riel@redhat.com>
Acked-by: Greg Thelen <gthelen@google.com>
Reviewed-by: Davidlohr Bueso <davidlohr@hp.com>
Cc: Manfred Spraul <manfred@colorfullife.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
This commit is contained in:
Rafael Aquini 2014-01-27 17:07:01 -08:00 committed by Linus Torvalds
parent 78f5009cc3
commit 0f3d2b0135
4 changed files with 41 additions and 19 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

7
ipc/msg.c
View File

@ -696,7 +696,7 @@ long do_msgsnd(int msqid, long mtype, void __user *mtext,
goto out_unlock0;
/* raced with RMID? */
if (msq->q_perm.deleted) {
if (!ipc_valid_object(&msq->q_perm)) {
err = -EIDRM;
goto out_unlock0;
}
@ -731,7 +731,8 @@ long do_msgsnd(int msqid, long mtype, void __user *mtext,
ipc_lock_object(&msq->q_perm);
ipc_rcu_putref(msq, ipc_rcu_free);
if (msq->q_perm.deleted) {
/* raced with RMID? */
if (!ipc_valid_object(&msq->q_perm)) {
err = -EIDRM;
goto out_unlock0;
}
@ -909,7 +910,7 @@ long do_msgrcv(int msqid, void __user *buf, size_t bufsz, long msgtyp, int msgfl
ipc_lock_object(&msq->q_perm);
/* raced with RMID? */
if (msq->q_perm.deleted) {
if (!ipc_valid_object(&msq->q_perm)) {
msg = ERR_PTR(-EIDRM);
goto out_unlock0;
}

24
ipc/sem.c
View File

@ -1284,7 +1284,7 @@ static int semctl_setval(struct ipc_namespace *ns, int semid, int semnum,
sem_lock(sma, NULL, -1);
if (sma->sem_perm.deleted) {
if (!ipc_valid_object(&sma->sem_perm)) {
sem_unlock(sma, -1);
rcu_read_unlock();
return -EIDRM;
@ -1344,7 +1344,7 @@ static int semctl_main(struct ipc_namespace *ns, int semid, int semnum,
int i;
sem_lock(sma, NULL, -1);
if (sma->sem_perm.deleted) {
if (!ipc_valid_object(&sma->sem_perm)) {
err = -EIDRM;
goto out_unlock;
}
@ -1363,7 +1363,7 @@ static int semctl_main(struct ipc_namespace *ns, int semid, int semnum,
rcu_read_lock();
sem_lock_and_putref(sma);
if (sma->sem_perm.deleted) {
if (!ipc_valid_object(&sma->sem_perm)) {
err = -EIDRM;
goto out_unlock;
}
@ -1411,7 +1411,7 @@ static int semctl_main(struct ipc_namespace *ns, int semid, int semnum,
}
rcu_read_lock();
sem_lock_and_putref(sma);
if (sma->sem_perm.deleted) {
if (!ipc_valid_object(&sma->sem_perm)) {
err = -EIDRM;
goto out_unlock;
}
@ -1437,7 +1437,7 @@ static int semctl_main(struct ipc_namespace *ns, int semid, int semnum,
goto out_rcu_wakeup;
sem_lock(sma, NULL, -1);
if (sma->sem_perm.deleted) {
if (!ipc_valid_object(&sma->sem_perm)) {
err = -EIDRM;
goto out_unlock;
}
@ -1701,7 +1701,7 @@ static struct sem_undo *find_alloc_undo(struct ipc_namespace *ns, int semid)
/* step 3: Acquire the lock on semaphore array */
rcu_read_lock();
sem_lock_and_putref(sma);
if (sma->sem_perm.deleted) {
if (!ipc_valid_object(&sma->sem_perm)) {
sem_unlock(sma, -1);
rcu_read_unlock();
kfree(new);
@ -1848,7 +1848,15 @@ SYSCALL_DEFINE4(semtimedop, int, semid, struct sembuf __user *, tsops,
error = -EIDRM;
locknum = sem_lock(sma, sops, nsops);
if (sma->sem_perm.deleted)
/*
* 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_free;
/*
* semid identifiers are not unique - find_alloc_undo may have
@ -2070,7 +2078,7 @@ void exit_sem(struct task_struct *tsk)
sem_lock(sma, NULL, -1);
/* exit_sem raced with IPC_RMID, nothing to do */
if (sma->sem_perm.deleted) {
if (!ipc_valid_object(&sma->sem_perm)) {
sem_unlock(sma, -1);
rcu_read_unlock();
continue;

16
ipc/shm.c
View File

@ -975,6 +975,13 @@ SYSCALL_DEFINE3(shmctl, int, shmid, int, cmd, struct shmid_ds __user *, buf)
goto out_unlock1;
ipc_lock_object(&shp->shm_perm);
/* check if shm_destroy() is tearing down shp */
if (!ipc_valid_object(&shp->shm_perm)) {
err = -EIDRM;
goto out_unlock0;
}
if (!ns_capable(ns->user_ns, CAP_IPC_LOCK)) {
kuid_t euid = current_euid();
if (!uid_eq(euid, shp->shm_perm.uid) &&
@ -989,13 +996,6 @@ SYSCALL_DEFINE3(shmctl, int, shmid, int, cmd, struct shmid_ds __user *, buf)
}
shm_file = shp->shm_file;
/* check if shm_destroy() is tearing down shp */
if (shm_file == NULL) {
err = -EIDRM;
goto out_unlock0;
}
if (is_file_hugepages(shm_file))
goto out_unlock0;
@ -1116,7 +1116,7 @@ long do_shmat(int shmid, char __user *shmaddr, int shmflg, ulong *raddr,
ipc_lock_object(&shp->shm_perm);
/* check if shm_destroy() is tearing down shp */
if (shp->shm_file == NULL) {
if (!ipc_valid_object(&shp->shm_perm)) {
ipc_unlock_object(&shp->shm_perm);
err = -EIDRM;
goto out_unlock;

13
ipc/util.h
View File

@ -185,6 +185,19 @@ static inline void ipc_unlock(struct kern_ipc_perm *perm)
rcu_read_unlock();
}
/*
* ipc_valid_object() - helper to sort out IPC_RMID races for codepaths
* where the respective ipc_ids.rwsem is not being held down.
* Checks whether the ipc object is still around or if it's gone already, as
* ipc_rmid() may have already freed the ID while the ipc lock was spinning.
* Needs to be called with kern_ipc_perm.lock held -- exception made for one
* checkpoint case at sys_semtimedop() as noted in code commentary.
*/
static inline bool ipc_valid_object(struct kern_ipc_perm *perm)
{
return perm->deleted == 0;
}
struct kern_ipc_perm *ipc_obtain_object_check(struct ipc_ids *ids, int id);
int ipcget(struct ipc_namespace *ns, struct ipc_ids *ids,
struct ipc_ops *ops, struct ipc_params *params);