ipc,msg: prevent race with rmid in msgsnd,msgrcv
authorDavidlohr Bueso <davidlohr@hp.com>
Mon, 30 Sep 2013 20:45:26 +0000 (13:45 -0700)
committerGreg Kroah-Hartman <gregkh@linuxfoundation.org>
Fri, 18 Oct 2013 14:45:48 +0000 (07:45 -0700)
commit3232569ecd21ad181bd070acdb27ac5ccd54494c
tree7a9c05fa9248a387377b10822dac52be773d0d23
parente556ea0191d648c63fbc4fe24bbfb15ad872a205
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>
ipc/msg.c