linux-kernel - [PATCH 13/20] ipc/sem.c: Avoid ipc_rcu_putref for failed ipc

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Date:   Thu, 25 May 2017 20:51:00 +0200
From:   Manfred Spraul <manfred@...orfullife.com>
To:     mtk.manpages@...il.com, Andrew Morton <akpm@...ux-foundation.org>,
        Kees Cook <keescook@...omium.org>
Cc:     LKML <linux-kernel@...r.kernel.org>, 1vier1@....de,
        Davidlohr Bueso <dave@...olabs.net>, mingo@...nel.org,
        peterz@...radead.org, fabf@...net.be,
        Manfred Spraul <manfred@...orfullife.com>
Subject: [PATCH 13/20] ipc/sem.c: Avoid ipc_rcu_putref for failed ipc_addid()

Loosely based on a patch from Kees Cook <keescook@...omium.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().

Signed-off-by: Manfred Spraul <manfred@...orfullife.com>
Cc: Kees Cook <keescook@...omium.org>
---
 ipc/sem.c | 9 ++++-----
 1 file changed, 4 insertions(+), 5 deletions(-)

diff --git a/ipc/sem.c b/ipc/sem.c
index 445a5b5..2b2ed56 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;
 
-- 
2.9.3