tcp: tcp_replace_ts_recent() should not be called from tcp_validate_incoming()

We added support for RFC 5961 in latest kernels but TCP fails
to perform exhaustive check of ACK sequence.

We can update our view of peer tsval from a frame that is
later discarded by tcp_ack()

This makes timestamps enabled sessions vulnerable to injection of
a high tsval : peers start an ACK storm, since the victim
sends a dupack each time it receives an ACK from the other peer.

As tcp_validate_incoming() is called before tcp_ack(), we should
not peform tcp_replace_ts_recent() from it, and let callers do it
at the right time.

Signed-off-by: Eric Dumazet <edumazet@google.com>
Cc: Neal Cardwell <ncardwell@google.com>
Cc: Yuchung Cheng <ycheng@google.com>
Cc: Nandita Dukkipati <nanditad@google.com>
Cc: H.K. Jerry Chu <hkchu@google.com>
Cc: Romain Francoise <romain@orebokech.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 10 insertions, 5 deletions

diff --git a/net/ipv4/tcp_input.c b/net/ipv4/tcp_input.c
index 2c2b13a999ea..609ff98aeb47 100644
--- a/net/ipv4/tcp_input.c
+++ b/net/ipv4/tcp_input.c
@@ -5313,11 +5313,6 @@ static bool tcp_validate_incoming(struct sock *sk, struct sk_buff *skb,
                 goto discard;
         }
 
-        /* ts_recent update must be made after we are sure that the packet
-         * is in window.
-         */
-        tcp_replace_ts_recent(tp, TCP_SKB_CB(skb)->seq);
-
         /* step 3: check security and precedence [ignored] */
 
         /* step 4: Check for a SYN
@@ -5552,6 +5547,11 @@ step5:
         if (th->ack && tcp_ack(sk, skb, FLAG_SLOWPATH) < 0)
                 goto discard;
 
+        /* ts_recent update must be made after we are sure that the packet
+         * is in window.
+         */
+        tcp_replace_ts_recent(tp, TCP_SKB_CB(skb)->seq);
+
         tcp_rcv_rtt_measure_ts(sk, skb);
 
         /* Process urgent data. */
@@ -6130,6 +6130,11 @@ int tcp_rcv_state_process(struct sock *sk, struct sk_buff *skb,
         } else
                 goto discard;
 
+        /* ts_recent update must be made after we are sure that the packet
+         * is in window.
+         */
+        tcp_replace_ts_recent(tp, TCP_SKB_CB(skb)->seq);
+
         /* step 6: check the URG bit */
         tcp_urg(sk, skb, th);