path: root/ipc
diff options
authorManfred Spraul <manfred@colorfullife.com>2013-09-03 16:00:08 +0200
committerLinus Torvalds <torvalds@linux-foundation.org>2013-09-03 10:42:56 -0700
commitbebcb928c820d0ee83aca4b192adc195e43e66a2 (patch)
tree28ad45577c7e65e28938eed04b0459674a11f0e3 /ipc
parentec1882a9391c55332ebf3d1654f40b76e4a6c010 (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>
Diffstat (limited to 'ipc')
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();