linux-kernel - [PATCH 11/20] ipc/msg: Avoid ipc_rcu

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Date:   Thu, 25 May 2017 20:50:58 +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 11/20] ipc/msg: Avoid ipc_rcu_alloc()

From: Kees Cook <keescook@...omium.org>

Instead of using ipc_rcu_alloc() which only performs the refcount
bump, open code it. This also allows for msg_queue structure
layout to be randomized in the future.

Signed-off-by: Kees Cook <keescook@...omium.org>
Signed-off-by: Manfred Spraul <manfred@...orfullife.com>
---
 ipc/msg.c | 18 ++++++++++++++----
 1 file changed, 14 insertions(+), 4 deletions(-)

diff --git a/ipc/msg.c b/ipc/msg.c
index 25d43e2..10094a7 100644
--- a/ipc/msg.c
+++ b/ipc/msg.c
@@ -109,6 +109,19 @@ static void msg_rcu_free(struct rcu_head *head)
 	__msg_free(msq);
 }
 
+static struct msg_queue *msg_alloc(void)
+{
+	struct msg_queue *msq;
+
+	msq = kvmalloc(sizeof(*msq), GFP_KERNEL);
+	if (unlikely(!msq))
+		return NULL;
+
+	atomic_set(&msq->q_perm.refcount, 1);
+
+	return msq;
+}
+
 /**
  * newque - Create a new msg queue
  * @ns: namespace
@@ -123,10 +136,7 @@ static int newque(struct ipc_namespace *ns, struct ipc_params *params)
 	key_t key = params->key;
 	int msgflg = params->flg;
 
-	BUILD_BUG_ON(offsetof(struct msg_queue, q_perm) != 0);
-
-	msq = container_of(ipc_rcu_alloc(sizeof(*msq)), struct msg_queue,
-				q_perm);
+	msq = msg_alloc();
 	if (!msq)
 		return -ENOMEM;
 
-- 
2.9.3