This is a note to let you know that I've just added the patch titled ipc/msg.c: Fix lost wakeup in msgsnd(). to the 3.11-stable tree which can be found at: http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary The filename of the patch is: ipc-msg.c-fix-lost-wakeup-in-msgsnd.patch and it can be found in the queue-3.11 subdirectory. If you, or anyone else, feels it should not be added to the stable tree, please let <stable@xxxxxxxxxxxxxxx> know about it. >From bebcb928c820d0ee83aca4b192adc195e43e66a2 Mon Sep 17 00:00:00 2001 From: Manfred Spraul <manfred@xxxxxxxxxxxxxxxx> Date: Tue, 3 Sep 2013 16:00:08 +0200 Subject: ipc/msg.c: Fix lost wakeup in msgsnd(). From: Manfred Spraul <manfred@xxxxxxxxxxxxxxxx> commit bebcb928c820d0ee83aca4b192adc195e43e66a2 upstream. 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@xxxxxxxxxxxx> Acked-by: Rik van Riel <riel@xxxxxxxxxx> Signed-off-by: Manfred Spraul <manfred@xxxxxxxxxxxxxxxx> Signed-off-by: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx> Cc: Sedat Dilek <sedat.dilek@xxxxxxxxx> Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx> --- ipc/msg.c | 12 +++++------- 1 file changed, 5 insertions(+), 7 deletions(-) --- a/ipc/msg.c +++ b/ipc/msg.c @@ -680,16 +680,18 @@ long do_msgsnd(int msqid, long mtype, vo 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, vo /* 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, vo 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(); Patches currently in stable-queue which might be from manfred@xxxxxxxxxxxxxxxx are queue-3.11/ipc-msg.c-fix-lost-wakeup-in-msgsnd.patch -- To unsubscribe from this list: send the line "unsubscribe stable" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html