tcp: fix potential memory corruption

[ 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@google.com>
Cc: Hans Westgaard Ry <hans.westgaard.ry@oracle.com>
Cc: Håkon Bugge <haakon.bugge@oracle.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Jiri Slaby <jslaby@suse.cz>

diff --git a/net/ipv4/tcp.c b/net/ipv4/tcp.c
index 392d3259f9ad57dc4c3a492fa251d8100231ee52..3e63b5fb2121d00a4ada1bb36645e9ed03c36ba0 100644 (file)
--- 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;
                                        }