diff options
| author | Manfred Spraul | 2013-09-03 16:00:08 +0200 |
|---|---|---|
| committer | Linus Torvalds | 2013-09-03 10:42:56 -0700 |
| commit | bebcb928c820d0ee83aca4b192adc195e43e66a2 (patch) | |
| tree | 28ad45577c7e65e28938eed04b0459674a11f0e3 | |
| parent | ec1882a9391c55332ebf3d1654f40b76e4a6c010 (diff) | |
ipc/msg.c: Fix lost wakeup in msgsnd().
The check if the queue is full and adding current to the wait queue of
pending msgsnd() operations (ss_add()) must be atomic.
Otherwise:
- the thread that performs msgsnd() finds a full queue and decides to
sleep.
- the thread that performs msgrcv() first reads all messages from the
queue and then sleeps, because the queue is empty.
- the msgrcv() calls do not perform any wakeups, because the msgsnd()
task has not yet called ss_add().
- then the msgsnd()-thread first calls ss_add() and then sleeps.
Net result: msgsnd() and msgrcv() both sleep forever.
Observed with msgctl08 from ltp with a preemptible kernel.
Fix: Call ipc_lock_object() before performing the check.
The patch also moves security_msg_queue_msgsnd() under ipc_lock_object:
- msgctl(IPC_SET) explicitely mentions that it tries to expunge any
pending operations that are not allowed anymore with the new
permissions. If security_msg_queue_msgsnd() is called without locks,
then there might be races.
- it makes the patch much simpler.
Reported-and-tested-by: Vineet Gupta <Vineet.Gupta1@synopsys.com>
Acked-by: Rik van Riel <riel@redhat.com>
Cc: stable@vger.kernel.org # for 3.11
Signed-off-by: Manfred Spraul <manfred@colorfullife.com>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
| -rw-r--r-- | ipc/msg.c | 12 |
1 files changed, 5 insertions, 7 deletions
diff --git a/ipc/msg.c b/ipc/msg.c index 9f29d9e89bac..b65fdf1a09dd 100644 --- a/ipc/msg.c +++ b/ipc/msg.c @@ -680,16 +680,18 @@ long do_msgsnd(int msqid, long mtype, void __user *mtext, goto out_unlock1; } + ipc_lock_object(&msq->q_perm); + for (;;) { struct msg_sender s; err = -EACCES; if (ipcperms(ns, &msq->q_perm, S_IWUGO)) - goto out_unlock1; + goto out_unlock0; err = security_msg_queue_msgsnd(msq, msg, msgflg); if (err) - goto out_unlock1; + goto out_unlock0; if (msgsz + msq->q_cbytes <= msq->q_qbytes && 1 + msq->q_qnum <= msq->q_qbytes) { @@ -699,10 +701,9 @@ long do_msgsnd(int msqid, long mtype, void __user *mtext, /* queue full, wait: */ if (msgflg & IPC_NOWAIT) { err = -EAGAIN; - goto out_unlock1; + goto out_unlock0; } - ipc_lock_object(&msq->q_perm); ss_add(msq, &s); if (!ipc_rcu_getref(msq)) { @@ -730,10 +731,7 @@ long do_msgsnd(int msqid, long mtype, void __user *mtext, goto out_unlock0; } - ipc_unlock_object(&msq->q_perm); } - - ipc_lock_object(&msq->q_perm); msq->q_lspid = task_tgid_vnr(current); msq->q_stime = get_seconds(); |