linux-kernel - [PATCH 3.12 101/127] tcp: fix potential memory corruption

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Date:   Fri, 25 Nov 2016 09:30:14 +0100
From:   Jiri Slaby <jslaby@...e.cz>
To:     stable@...r.kernel.org
Cc:     linux-kernel@...r.kernel.org, Eric Dumazet <edumazet@...gle.com>,
        Hans Westgaard Ry <hans.westgaard.ry@...cle.com>,
        Håkon Bugge <haakon.bugge@...cle.com>,
        "David S . Miller" <davem@...emloft.net>,
        Jiri Slaby <jslaby@...e.cz>
Subject: [PATCH 3.12 101/127] tcp: fix potential memory corruption

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

3.12-stable review patch.  If anyone has any objections, please let me know.

===============

[ Upstream commit ac9e70b17ecd7c6e933ff2eaf7ab37429e71bf4d ]

Imagine initial value of max_skb_frags is 17, and last
skb in write queue has 15 frags.

Then max_skb_frags is lowered to 14 or smaller value.

tcp_sendmsg() will then be allowed to add additional page frags
and eventually go past MAX_SKB_FRAGS, overflowing struct
skb_shared_info.

Fixes: 5f74f82ea34c ("net:Add sysctl_max_skb_frags")
Signed-off-by: Eric Dumazet <edumazet@...gle.com>
Cc: Hans Westgaard Ry <hans.westgaard.ry@...cle.com>
Cc: Håkon Bugge <haakon.bugge@...cle.com>
Signed-off-by: David S. Miller <davem@...emloft.net>
Signed-off-by: Jiri Slaby <jslaby@...e.cz>
---
 net/ipv4/tcp.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/net/ipv4/tcp.c b/net/ipv4/tcp.c
index 392d3259f9ad..3e63b5fb2121 100644
--- a/net/ipv4/tcp.c
+++ b/net/ipv4/tcp.c
@@ -1169,7 +1169,7 @@ new_segment:
 
 				if (!skb_can_coalesce(skb, i, pfrag->page,
 						      pfrag->offset)) {
-					if (i == sysctl_max_skb_frags || !sg) {
+					if (i >= sysctl_max_skb_frags || !sg) {
 						tcp_mark_push(tp, skb);
 						goto new_segment;
 					}
-- 
2.10.2