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authorRafael Aquini <aquini@redhat.com>2014-01-27 17:07:01 -0800
committerLinus Torvalds <torvalds@linux-foundation.org>2014-01-27 21:02:39 -0800
commit0f3d2b0135f4bdbfe47a99753923a64efd373d11 (patch)
tree4b211b7502e2412aedd94400bdcb012a2b5814b3 /ipc/sem.c
parent78f5009cc35eb5e52d276a046d90ee2f41b60f8c (diff)
downloadop-kernel-dev-0f3d2b0135f4bdbfe47a99753923a64efd373d11.zip
op-kernel-dev-0f3d2b0135f4bdbfe47a99753923a64efd373d11.tar.gz
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>
Diffstat (limited to 'ipc/sem.c')
-rw-r--r--ipc/sem.c24
1 files changed, 16 insertions, 8 deletions
diff --git a/ipc/sem.c b/ipc/sem.c
index cc9ac35..4d88194 100644
--- a/ipc/sem.c
+++ b/ipc/sem.c
@@ -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;
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