From 37561f68bd527ec39076e32effdc7b1dcdfb17ea Mon Sep 17 00:00:00 2001 From: Jerry Chu Date: Mon, 22 Oct 2012 11:26:36 +0000 Subject: [PATCH] tcp: Reject invalid ack_seq to Fast Open sockets A packet with an invalid ack_seq may cause a TCP Fast Open socket to switch to the unexpected TCP_CLOSING state, triggering a BUG_ON kernel panic. When a FIN packet with an invalid ack_seq# arrives at a socket in the TCP_FIN_WAIT1 state, rather than discarding the packet, the current code will accept the FIN, causing state transition to TCP_CLOSING. This may be a small deviation from RFC793, which seems to say that the packet should be dropped. Unfortunately I did not expect this case for Fast Open hence it will trigger a BUG_ON panic. It turns out there is really nothing bad about a TFO socket going into TCP_CLOSING state so I could just remove the BUG_ON statements. But after some thought I think it's better to treat this case like TCP_SYN_RECV and return a RST to the confused peer who caused the unacceptable ack_seq to be generated in the first place. Signed-off-by: H.K. Jerry Chu Cc: Neal Cardwell Cc: Yuchung Cheng Acked-by: Yuchung Cheng Acked-by: Eric Dumazet Acked-by: Neal Cardwell Signed-off-by: David S. Miller --- net/ipv4/tcp_input.c | 12 ++++++++++-- net/ipv4/tcp_timer.c | 4 ++-- 2 files changed, 12 insertions(+), 4 deletions(-) diff --git a/net/ipv4/tcp_input.c b/net/ipv4/tcp_input.c index 036f85738141..1db663983587 100644 --- a/net/ipv4/tcp_input.c +++ b/net/ipv4/tcp_input.c @@ -5964,7 +5964,7 @@ int tcp_rcv_state_process(struct sock *sk, struct sk_buff *skb, req = tp->fastopen_rsk; if (req != NULL) { - BUG_ON(sk->sk_state != TCP_SYN_RECV && + WARN_ON_ONCE(sk->sk_state != TCP_SYN_RECV && sk->sk_state != TCP_FIN_WAIT1); if (tcp_check_req(sk, skb, req, NULL, true) == NULL) @@ -6053,7 +6053,15 @@ int tcp_rcv_state_process(struct sock *sk, struct sk_buff *skb, * ACK we have received, this would have acknowledged * our SYNACK so stop the SYNACK timer. */ - if (acceptable && req != NULL) { + if (req != NULL) { + /* Return RST if ack_seq is invalid. + * Note that RFC793 only says to generate a + * DUPACK for it but for TCP Fast Open it seems + * better to treat this case like TCP_SYN_RECV + * above. + */ + if (!acceptable) + return 1; /* We no longer need the request sock. */ reqsk_fastopen_remove(sk, req, false); tcp_rearm_rto(sk); diff --git a/net/ipv4/tcp_timer.c b/net/ipv4/tcp_timer.c index fc04711e80c8..d47c1b4421a3 100644 --- a/net/ipv4/tcp_timer.c +++ b/net/ipv4/tcp_timer.c @@ -347,8 +347,8 @@ void tcp_retransmit_timer(struct sock *sk) return; } if (tp->fastopen_rsk) { - BUG_ON(sk->sk_state != TCP_SYN_RECV && - sk->sk_state != TCP_FIN_WAIT1); + WARN_ON_ONCE(sk->sk_state != TCP_SYN_RECV && + sk->sk_state != TCP_FIN_WAIT1); tcp_fastopen_synack_timer(sk); /* Before we receive ACK to our SYN-ACK don't retransmit * anything else (e.g., data or FIN segments). -- 2.34.1