ipc/sem.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_sem_free().

Link: http://lkml.kernel.org/r/20170525185107.12869-14-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>

1 files changed, 4 insertions, 5 deletions

diff --git a/ipc/sem.c b/ipc/sem.c
index 445a5b5eb88f..2b2ed56e0fde 100644
--- a/ipc/sem.c
+++ b/ipc/sem.c
@@ -479,7 +479,6 @@ static struct sem_array *sem_alloc(size_t nsems)
  */
 static int newary(struct ipc_namespace *ns, struct ipc_params *params)
 {
-        int id;
         int retval;
         struct sem_array *sma;
         key_t key = params->key;
@@ -520,10 +519,10 @@ static int newary(struct ipc_namespace *ns, struct ipc_params *params)
         sma->sem_nsems = nsems;
         sma->sem_ctime = get_seconds();
 
-        id = ipc_addid(&sem_ids(ns), &sma->sem_perm, ns->sc_semmni);
-        if (id < 0) {
-                ipc_rcu_putref(&sma->sem_perm, sem_rcu_free);
-                return id;
+        retval = ipc_addid(&sem_ids(ns), &sma->sem_perm, ns->sc_semmni);
+        if (retval < 0) {
+                call_rcu(&sma->sem_perm.rcu, sem_rcu_free);
+                return retval;
         }
         ns->used_sems += nsems;