ipc/msg.c: avoid ipc_rcu_putref for failed ipc_addid()

Loosely based on a patch from Kees Cook <keescook@chromium.org>:
 - id and retval can be merged
 - if ipc_addid() fails, then use call_rcu() directly.

The difference is that call_rcu is used for failed ipc_addid() calls, to
continue to guaranteed an rcu delay for security_msg_queue_free().

Link: http://lkml.kernel.org/r/20170525185107.12869-16-manfred@colorfullife.com
Signed-off-by: Manfred Spraul <manfred@colorfullife.com>
Cc: Kees Cook <keescook@chromium.org>
Cc: Davidlohr Bueso <dave@stgolabs.net>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

diff --git a/ipc/msg.c b/ipc/msg.c
index 10094a7..cd90bfd 100644 (file)
--- a/ipc/msg.c
+++ b/ipc/msg.c
@@ -132,7 +132,7 @@ static struct msg_queue *msg_alloc(void)
 static int newque(struct ipc_namespace *ns, struct ipc_params *params)
 {
        struct msg_queue *msq;
-       int id, retval;
+       int retval;
        key_t key = params->key;
        int msgflg = params->flg;
 
@@ -160,10 +160,10 @@ static int newque(struct ipc_namespace *ns, struct ipc_params *params)
        INIT_LIST_HEAD(&msq->q_senders);
 
        /* ipc_addid() locks msq upon success. */
-       id = ipc_addid(&msg_ids(ns), &msq->q_perm, ns->msg_ctlmni);
-       if (id < 0) {
-               ipc_rcu_putref(&msq->q_perm, msg_rcu_free);
-               return id;
+       retval = ipc_addid(&msg_ids(ns), &msq->q_perm, ns->msg_ctlmni);
+       if (retval < 0) {
+               call_rcu(&msq->q_perm.rcu, msg_rcu_free);
+               return retval;
        }
 
        ipc_unlock_object(&msq->q_perm);