From: Xia Fukun <xiafukun@huawei.com> stable inclusion from stable-v4.19.269 commit a1504a9e205691940d44bf94ad33267eefea3b5e category: bugfix bugzilla: https://gitee.com/openeuler/kernel/issues/I6994X CVE: NA Reference: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?h=l... -------------------------------- [ Upstream commit b52be557e24c47286738276121177a41f54e3b83 ] When __do_semtimedop() goes to sleep because it has to wait for a semaphore value becoming zero or becoming bigger than some threshold, it links the on-stack sem_queue to the sem_array, then goes to sleep without holding a reference on the sem_array. When __do_semtimedop() comes back out of sleep, one of two things must happen: a) We prove that the on-stack sem_queue has been disconnected from the (possibly freed) sem_array, making it safe to return from the stack frame that the sem_queue exists in. b) We stabilize our reference to the sem_array, lock the sem_array, and detach the sem_queue from the sem_array ourselves. sem_array has RCU lifetime, so for case (b), the reference can be stabilized inside an RCU read-side critical section by locklessly checking whether the sem_queue is still connected to the sem_array. However, the current code does the lockless check on sem_queue before starting an RCU read-side critical section, so the result of the lockless check immediately becomes useless. Fix it by doing rcu_read_lock() before the lockless check. Now RCU ensures that if we observe the object being on our queue, the object can't be freed until rcu_read_unlock(). This bug is only hittable on kernel builds with full preemption support (either CONFIG_PREEMPT or PREEMPT_DYNAMIC with preempt=full). Fixes: 370b262c896e ("ipc/sem: avoid idr tree lookup for interrupted semop") Cc: stable@vger.kernel.org Signed-off-by: Jann Horn <jannh@google.com> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org> Signed-off-by: Sasha Levin <sashal@kernel.org> Signed-off-by: Xia Fukun <xiafukun@huawei.com> Reviewed-by: ZhangQiao <zhangqiao22@huawei.com> Signed-off-by: Yongqiang Liu <liuyongqiang13@huawei.com> --- ipc/sem.c | 3 ++- 1 file changed, 2 insertions(+), 1 deletion(-) diff --git a/ipc/sem.c b/ipc/sem.c index 171881795a30..7c4595d1951c 100644 --- a/ipc/sem.c +++ b/ipc/sem.c @@ -2149,6 +2149,7 @@ static long do_semtimedop(int semid, struct sembuf __user *tsops, * 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) { /* @@ -2158,10 +2159,10 @@ static long do_semtimedop(int semid, struct sembuf __user *tsops, * overwritten by the previous owner of the semaphore. */ smp_mb(); + rcu_read_unlock(); goto out_free; } - rcu_read_lock(); locknum = sem_lock(sma, sops, nsops); if (!ipc_valid_object(&sma->sem_perm)) -- 2.25.1