commit b9a532277938798b53178d5a66af6e2915cb27cf
author Linus Torvalds <torvalds@linux-foundation.org> Wed Sep 30 12:48:40 2015 -0400
committer Linus Torvalds <torvalds@linux-foundation.org> Wed Sep 30 12:48:40 2015 -0400
tree 61938755aa03a1fcde29b3fcea8b29ef962af58f
parent 3225031fbeb1e32b269a82eccd815128267a4bfe

Initialize msg/shm IPC objects before doing ipc_addid()

As reported by Dmitry Vyukov, we really shouldn't do ipc_addid() before
having initialized the IPC object state.  Yes, we initialize the IPC
object in a locked state, but with all the lockless RCU lookup work,
that IPC object lock no longer means that the state cannot be seen.

We already did this for the IPC semaphore code (see commit e8577d1f0329:
"ipc/sem.c: fully initialize sem_array before making it visible") but we
clearly forgot about msg and shm.

Reported-by: Dmitry Vyukov <dvyukov@google.com>
Cc: Manfred Spraul <manfred@colorfullife.com>
Cc: Davidlohr Bueso <dbueso@suse.de>
Cc: stable@vger.kernel.org
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

ipc/shm.c

diff --git a/ipc/shm.c b/ipc/shm.c
index 222131e..4178727 100644
--- a/ipc/shm.c
+++ b/ipc/shm.c
@@ -551,12 +551,6 @@
 	if (IS_ERR(file))
 		goto no_file;
 
-	id = ipc_addid(&shm_ids(ns), &shp->shm_perm, ns->shm_ctlmni);
-	if (id < 0) {
-		error = id;
-		goto no_id;
-	}
-
 	shp->shm_cprid = task_tgid_vnr(current);
 	shp->shm_lprid = 0;
 	shp->shm_atim = shp->shm_dtim = 0;
@@ -565,6 +559,13 @@
 	shp->shm_nattch = 0;
 	shp->shm_file = file;
 	shp->shm_creator = current;
+
+	id = ipc_addid(&shm_ids(ns), &shp->shm_perm, ns->shm_ctlmni);
+	if (id < 0) {
+		error = id;
+		goto no_id;
+	}
+
 	list_add(&shp->shm_clist, &current->sysvshm.shm_clist);
 
 	/*