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authorEric Dumazet <edumazet@google.com>2012-07-17 16:29:30 +0400
committerBen Hutchings <ben@decadent.org.uk>2013-01-16 05:13:26 +0400
commitd37f92d306c41ebd908bcdef373dea512b17cafb (patch)
tree82d27d22c8a6bbe89a02bcd9468614721a3cbea6 /net/ipv4
parent481079c4df95e11d3893b92fa4000f58e1cd713b (diff)
downloadlinux-d37f92d306c41ebd908bcdef373dea512b17cafb.tar.xz
tcp: refine SYN handling in tcp_validate_incoming
[ Upstream commit e371589917011efe6ff8c7dfb4e9e81934ac5855 ] Followup of commit 0c24604b68fc (tcp: implement RFC 5961 4.2) As reported by Vijay Subramanian, we should send a challenge ACK instead of a dup ack if a SYN flag is set on a packet received out of window. This permits the ratelimiting to work as intended, and to increase correct SNMP counters. Suggested-by: Vijay Subramanian <subramanian.vijay@gmail.com> Signed-off-by: Eric Dumazet <edumazet@google.com> Acked-by: Vijay Subramanian <subramanian.vijay@gmail.com> Cc: Kiran Kumar Kella <kkiran@broadcom.com> Signed-off-by: David S. Miller <davem@davemloft.net> Signed-off-by: Ben Hutchings <ben@decadent.org.uk>
Diffstat (limited to 'net/ipv4')
-rw-r--r--net/ipv4/tcp_input.c6
1 files changed, 5 insertions, 1 deletions
diff --git a/net/ipv4/tcp_input.c b/net/ipv4/tcp_input.c
index 0b9d8d4d92dd..de434bc4355a 100644
--- a/net/ipv4/tcp_input.c
+++ b/net/ipv4/tcp_input.c
@@ -5289,8 +5289,11 @@ static bool tcp_validate_incoming(struct sock *sk, struct sk_buff *skb,
* an acknowledgment should be sent in reply (unless the RST
* bit is set, if so drop the segment and return)".
*/
- if (!th->rst)
+ if (!th->rst) {
+ if (th->syn)
+ goto syn_challenge;
tcp_send_dupack(sk, skb);
+ }
goto discard;
}
@@ -5320,6 +5323,7 @@ static bool tcp_validate_incoming(struct sock *sk, struct sk_buff *skb,
* RFC 5691 4.2 : Send a challenge ack
*/
if (th->syn) {
+syn_challenge:
if (syn_inerr)
TCP_INC_STATS_BH(sock_net(sk), TCP_MIB_INERRS);
NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_TCPSYNCHALLENGE);