linux-kernel - [PATCH 3.4 110/125] net: possible use after free in dst

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Date:   Wed, 12 Oct 2016 20:33:46 +0800
From:   lizf@...nel.org
To:     stable@...r.kernel.org
Cc:     linux-kernel@...r.kernel.org,
        Francesco Ruggeri <fruggeri@...stanetworks.com>,
        Francesco Ruggeri <fruggeri@...sta.com>,
        "David S. Miller" <davem@...emloft.net>,
        Zefan Li <lizefan@...wei.com>
Subject: [PATCH 3.4 110/125] net: possible use after free in dst_release

From: Francesco Ruggeri <fruggeri@...stanetworks.com>

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

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


commit 07a5d38453599052aff0877b16bb9c1585f08609 upstream.

dst_release should not access dst->flags after decrementing
__refcnt to 0. The dst_entry may be in dst_busy_list and
dst_gc_task may dst_destroy it before dst_release gets a chance
to access dst->flags.

Fixes: d69bbf88c8d0 ("net: fix a race in dst_release()")
Fixes: 27b75c95f10d ("net: avoid RCU for NOCACHE dst")
Signed-off-by: Francesco Ruggeri <fruggeri@...sta.com>
Acked-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 | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/net/core/dst.c b/net/core/dst.c
index 54ba1eb..48cff89 100644
--- a/net/core/dst.c
+++ b/net/core/dst.c
@@ -269,10 +269,11 @@ void dst_release(struct dst_entry *dst)
 {
 	if (dst) {
 		int newrefcnt;
+		unsigned short nocache = dst->flags & DST_NOCACHE;
 
 		newrefcnt = atomic_dec_return(&dst->__refcnt);
 		WARN_ON(newrefcnt < 0);
-		if (!newrefcnt && unlikely(dst->flags & DST_NOCACHE)) {
+		if (!newrefcnt && unlikely(nocache)) {
 			dst = dst_destroy(dst);
 			if (dst)
 				__dst_free(dst);
-- 
1.9.1