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| author | Manfred Spraul <manfred@colorfullife.com> | 2017-01-10 16:57:48 -0800 |
|---|---|---|
| committer | Linus Torvalds <torvalds@linux-foundation.org> | 2017-01-10 18:31:55 -0800 |
| commit | c626bc46edb0fec289adfc86b02e07d34127ef6c (patch) | |
| tree | ccb40c675819b214308a5c72f7f955cf775837b8 | |
| parent | da0510c47519fe0999cffe316e1d370e29f952be (diff) | |
| download | linux-c626bc46edb0fec289adfc86b02e07d34127ef6c.tar.bz2 | |
ipc/sem.c: fix incorrect sem_lock pairing
Based on the syzcaller test case from dvyukov:
https://gist.githubusercontent.com/dvyukov/d0e5efefe4d7d6daed829f5c3ca26a40/raw/08d0a261fe3c987bed04fbf267e08ba04bd533ea/gistfile1.txt
The slow (i.e.: failure to acquire) syscall exit from semtimedop()
incorrectly assumed that the the same lock is acquired as it was at the
initial syscall entry.
This is wrong:
- thread A: single semop semop(), sleeps
- thread B: multi semop semop(), sleeps
- thread A: woken up by signal/timeout
With this sequence, the initial sem_lock() call locks the per-semaphore
spinlock, and it is unlocked with sem_unlock(). The call at the syscall
return locks the global spinlock. Because locknum is not updated, the
following sem_unlock() call unlocks the per-semaphore spinlock, which is
actually not locked.
The fix is trivial: Use the return value from sem_lock.
Fixes: 370b262c896e ("ipc/sem: avoid idr tree lookup for interrupted semop")
Link: http://lkml.kernel.org/r/1482215645-22328-1-git-send-email-manfred@colorfullife.com
Signed-off-by: Manfred Spraul <manfred@colorfullife.com>
Reported-by: Dmitry Vyukov <dvyukov@google.com>
Reported-by: Johanna Abrahamsson <johanna@mjao.org>
Tested-by: Johanna Abrahamsson <johanna@mjao.org>
Acked-by: Davidlohr Bueso <dave@stgolabs.net>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
| -rw-r--r-- | ipc/sem.c | 2 |
1 files changed, 1 insertions, 1 deletions
diff --git a/ipc/sem.c b/ipc/sem.c index e08b94851922..3ec5742b5640 100644 --- a/ipc/sem.c +++ b/ipc/sem.c @@ -1977,7 +1977,7 @@ SYSCALL_DEFINE4(semtimedop, int, semid, struct sembuf __user *, tsops, } rcu_read_lock(); - sem_lock(sma, sops, nsops); + locknum = sem_lock(sma, sops, nsops); if (!ipc_valid_object(&sma->sem_perm)) goto out_unlock_free; |