ipc: introduce ipc_valid_object() helper to sort out IPC_RMID races

After the locking semantics for the SysV IPC API got improved, a couple
of IPC_RMID race windows were opened because we ended up dropping the
'kern_ipc_perm.deleted' check performed way down in ipc_lock().  The
spotted races got sorted out by re-introducing the old test within the
racy critical sections.

This patch introduces ipc_valid_object() to consolidate the way we cope
with IPC_RMID races by using the same abstraction across the API
implementation.

Signed-off-by: Rafael Aquini <aquini@redhat.com>
Acked-by: Rik van Riel <riel@redhat.com>
Acked-by: Greg Thelen <gthelen@google.com>
Reviewed-by: Davidlohr Bueso <davidlohr@hp.com>
Cc: Manfred Spraul <manfred@colorfullife.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 4 insertions, 3 deletions

diff --git a/ipc/msg.c b/ipc/msg.c
index 558aa91186b6..8983ea57d970 100644
--- a/ipc/msg.c
+++ b/ipc/msg.c
@@ -696,7 +696,7 @@ long do_msgsnd(int msqid, long mtype, void __user *mtext,
                         goto out_unlock0;
 
                 /* raced with RMID? */
-                if (msq->q_perm.deleted) {
+                if (!ipc_valid_object(&msq->q_perm)) {
                         err = -EIDRM;
                         goto out_unlock0;
                 }
@@ -731,7 +731,8 @@ long do_msgsnd(int msqid, long mtype, void __user *mtext,
                 ipc_lock_object(&msq->q_perm);
 
                 ipc_rcu_putref(msq, ipc_rcu_free);
-                if (msq->q_perm.deleted) {
+                /* raced with RMID? */
+                if (!ipc_valid_object(&msq->q_perm)) {
                         err = -EIDRM;
                         goto out_unlock0;
                 }
@@ -909,7 +910,7 @@ long do_msgrcv(int msqid, void __user *buf, size_t bufsz, long msgtyp, int msgfl
                 ipc_lock_object(&msq->q_perm);
 
                 /* raced with RMID? */
-                if (msq->q_perm.deleted) {
+                if (!ipc_valid_object(&msq->q_perm)) {
                         msg = ERR_PTR(-EIDRM);
                         goto out_unlock0;
                 }