From b5b7db8d680464b1d631fd016f5e093419f0bfd9 Mon Sep 17 00:00:00 2001 From: Eric Dumazet Date: Tue, 19 Sep 2017 10:05:57 -0700 Subject: [PATCH] tcp: fastopen: fix on syn-data transmit failure Our recent change exposed a bug in TCP Fastopen Client that syzkaller found right away [1] When we prepare skb with SYN+DATA, we attempt to transmit it, and we update socket state as if the transmit was a success. In socket RTX queue we have two skbs, one with the SYN alone, and a second one containing the DATA. When (malicious) ACK comes in, we now complain that second one had no skb_mstamp. The proper fix is to make sure that if the transmit failed, we do not pretend we sent the DATA skb, and make it our send_head. When 3WHS completes, we can now send the DATA right away, without having to wait for a timeout. [1] WARNING: CPU: 0 PID: 100189 at net/ipv4/tcp_input.c:3117 tcp_clean_rtx_queue+0x2057/0x2ab0 net/ipv4/tcp_input.c:3117() WARN_ON_ONCE(last_ackt == 0); Modules linked in: CPU: 0 PID: 100189 Comm: syz-executor1 Not tainted Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011 0000000000000000 ffff8800b35cb1d8 ffffffff81cad00d 0000000000000000 ffffffff828a4347 ffff88009f86c080 ffffffff8316eb20 0000000000000d7f ffff8800b35cb220 ffffffff812c33c2 ffff8800baad2440 00000009d46575c0 Call Trace: [] __dump_stack [] dump_stack+0xc1/0x124 [] warn_slowpath_common+0xe2/0x150 [] warn_slowpath_null+0x2e/0x40 [] tcp_clean_rtx_queue+0x2057/0x2ab0 n [] tcp_ack+0x151d/0x3930 [] tcp_rcv_state_process+0x1c69/0x4fd0 [] tcp_v4_do_rcv+0x54f/0x7c0 [] sk_backlog_rcv [] __release_sock+0x12b/0x3a0 [] release_sock+0x5e/0x1c0 [] inet_wait_for_connect [] __inet_stream_connect+0x545/0xc50 [] tcp_sendmsg_fastopen [] tcp_sendmsg+0x2298/0x35a0 [] inet_sendmsg+0xe5/0x520 [] sock_sendmsg_nosec [] sock_sendmsg+0xcf/0x110 Fixes: 8c72c65b426b ("tcp: update skb->skb_mstamp more carefully") Fixes: 783237e8daf1 ("net-tcp: Fast Open client - sending SYN-data") Signed-off-by: Eric Dumazet Reported-by: Dmitry Vyukov Cc: Neal Cardwell Cc: Yuchung Cheng Acked-by: Yuchung Cheng Signed-off-by: David S. Miller --- net/ipv4/tcp_output.c | 9 +++++++++ 1 file changed, 9 insertions(+) diff --git a/net/ipv4/tcp_output.c b/net/ipv4/tcp_output.c index 517d737059d1..0bc9e46a5369 100644 --- a/net/ipv4/tcp_output.c +++ b/net/ipv4/tcp_output.c @@ -3389,6 +3389,10 @@ static int tcp_send_syn_data(struct sock *sk, struct sk_buff *syn) goto done; } + /* data was not sent, this is our new send_head */ + sk->sk_send_head = syn_data; + tp->packets_out -= tcp_skb_pcount(syn_data); + fallback: /* Send a regular SYN with Fast Open cookie request option */ if (fo->cookie.len > 0) @@ -3441,6 +3445,11 @@ int tcp_connect(struct sock *sk) */ tp->snd_nxt = tp->write_seq; tp->pushed_seq = tp->write_seq; + buff = tcp_send_head(sk); + if (unlikely(buff)) { + tp->snd_nxt = TCP_SKB_CB(buff)->seq; + tp->pushed_seq = TCP_SKB_CB(buff)->seq; + } TCP_INC_STATS(sock_net(sk), TCP_MIB_ACTIVEOPENS); /* Timer for repeating the SYN until an answer. */ -- 2.20.1