3.16.52-rc1 review patch. If anyone has any objections, please let me know.
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From: Eric Dumazet edumazet@google.com
commit b5b7db8d680464b1d631fd016f5e093419f0bfd9 upstream.
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: [<ffffffff81cad00d>] __dump_stack [<ffffffff81cad00d>] dump_stack+0xc1/0x124 [<ffffffff812c33c2>] warn_slowpath_common+0xe2/0x150 [<ffffffff812c361e>] warn_slowpath_null+0x2e/0x40 [<ffffffff828a4347>] tcp_clean_rtx_queue+0x2057/0x2ab0 n [<ffffffff828ae6fd>] tcp_ack+0x151d/0x3930 [<ffffffff828baa09>] tcp_rcv_state_process+0x1c69/0x4fd0 [<ffffffff828efb7f>] tcp_v4_do_rcv+0x54f/0x7c0 [<ffffffff8258aacb>] sk_backlog_rcv [<ffffffff8258aacb>] __release_sock+0x12b/0x3a0 [<ffffffff8258ad9e>] release_sock+0x5e/0x1c0 [<ffffffff8294a785>] inet_wait_for_connect [<ffffffff8294a785>] __inet_stream_connect+0x545/0xc50 [<ffffffff82886f08>] tcp_sendmsg_fastopen [<ffffffff82886f08>] tcp_sendmsg+0x2298/0x35a0 [<ffffffff82952515>] inet_sendmsg+0xe5/0x520 [<ffffffff8257152f>] sock_sendmsg_nosec [<ffffffff8257152f>] 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 edumazet@google.com Reported-by: Dmitry Vyukov dvyukov@google.com Cc: Neal Cardwell ncardwell@google.com Cc: Yuchung Cheng ycheng@google.com Acked-by: Yuchung Cheng ycheng@google.com Signed-off-by: David S. Miller davem@davemloft.net Signed-off-by: Ben Hutchings ben@decadent.org.uk --- net/ipv4/tcp_output.c | 9 +++++++++ 1 file changed, 9 insertions(+)
--- a/net/ipv4/tcp_output.c +++ b/net/ipv4/tcp_output.c @@ -3058,6 +3058,10 @@ static int tcp_send_syn_data(struct sock 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) @@ -3104,6 +3108,11 @@ 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. */