ipc,msg: prevent race with rmid in msgsnd,msgrcv

commit 4271b05a227dc6175b66c3d9941aeab09048aeb2 upstream.

This fixes a race in both msgrcv() and msgsnd() between finding the msg
and actually dealing with the queue, as another thread can delete shmid
underneath us if we are preempted before acquiring the
kern_ipc_perm.lock.

Manfred illustrates this nicely:

Assume a preemptible kernel that is preempted just after

    msq = msq_obtain_object_check(ns, msqid)

in do_msgrcv().  The only lock that is held is rcu_read_lock().

Now the other thread processes IPC_RMID.  When the first task is
resumed, then it will happily wait for messages on a deleted queue.

Fix this by checking for if the queue has been deleted after taking the
lock.

Signed-off-by: Davidlohr Bueso <davidlohr@hp.com>
Reported-by: Manfred Spraul <manfred@colorfullife.com>
Cc: Rik van Riel <riel@redhat.com>
Cc: Mike Galbraith <efault@gmx.de>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/ipc/msg.c b/ipc/msg.c
index b65fdf1a09dd1f81b32731bfa2fcb455389ea63c..3bf8da8a33b8573406f5a485cf35a75b2872848a 100644 (file)
--- a/ipc/msg.c
+++ b/ipc/msg.c
@@ -689,6 +689,12 @@ long do_msgsnd(int msqid, long mtype, void __user *mtext,
                if (ipcperms(ns, &msq->q_perm, S_IWUGO))
                        goto out_unlock0;
 
+               /* raced with RMID? */
+               if (msq->q_perm.deleted) {
+                       err = -EIDRM;
+                       goto out_unlock0;
+               }
+
                err = security_msg_queue_msgsnd(msq, msg, msgflg);
                if (err)
                        goto out_unlock0;
@@ -895,6 +901,13 @@ long do_msgrcv(int msqid, void __user *buf, size_t bufsz, long msgtyp, int msgfl
                        goto out_unlock1;
 
                ipc_lock_object(&msq->q_perm);
+
+               /* raced with RMID? */
+               if (msq->q_perm.deleted) {
+                       msg = ERR_PTR(-EIDRM);
+                       goto out_unlock0;
+               }
+
                msg = find_msg(msq, &msgtyp, mode);
                if (!IS_ERR(msg)) {
                        /*