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

[Jiri Slaby]

From: Eric Dumazet <edumazet@xxxxxxxxxx>

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@xxxxxxxxxx>
Cc: Hans Westgaard Ry <hans.westgaard.ry@xxxxxxxxxx>
Cc: HÃkon Bugge <haakon.bugge@xxxxxxxxxx>
Signed-off-by: David S. Miller <davem@xxxxxxxxxxxxx>
Signed-off-by: Jiri Slaby <jslaby@xxxxxxx>
---
 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