linux-kernel - [PATCH 3.4 010/125] net: fix a race in dst

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Date:   Wed, 12 Oct 2016 20:32:06 +0800
From:   lizf@...nel.org
To:     stable@...r.kernel.org
Cc:     linux-kernel@...r.kernel.org, Eric Dumazet <edumazet@...gle.com>,
        "David S. Miller" <davem@...emloft.net>,
        Zefan Li <lizefan@...wei.com>
Subject: [PATCH 3.4 010/125] net: fix a race in dst_release()

From: Eric Dumazet <edumazet@...gle.com>

3.4.113-rc1 review patch.  If anyone has any objections, please let me know.

------------------


commit d69bbf88c8d0b367cf3e3a052f6daadf630ee566 upstream.

Only cpu seeing dst refcount going to 0 can safely
dereference dst->flags.

Otherwise an other cpu might already have freed the dst.

Fixes: 27b75c95f10d ("net: avoid RCU for NOCACHE dst")
Reported-by: Greg Thelen <gthelen@...gle.com>
Signed-off-by: Eric Dumazet <edumazet@...gle.com>
Signed-off-by: David S. Miller <davem@...emloft.net>
[lizf: Backported to 3.4: adjust context]
Signed-off-by: Zefan Li <lizefan@...wei.com>
---
 net/core/dst.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/net/core/dst.c b/net/core/dst.c
index 43d94ce..54ba1eb 100644
--- a/net/core/dst.c
+++ b/net/core/dst.c
@@ -272,7 +272,7 @@ void dst_release(struct dst_entry *dst)
 
 		newrefcnt = atomic_dec_return(&dst->__refcnt);
 		WARN_ON(newrefcnt < 0);
-		if (unlikely(dst->flags & DST_NOCACHE) && !newrefcnt) {
+		if (!newrefcnt && unlikely(dst->flags & DST_NOCACHE)) {
 			dst = dst_destroy(dst);
 			if (dst)
 				__dst_free(dst);
-- 
1.9.1