From 2dda640040876cd8ae646408b69eea40c24f9ae9 Mon Sep 17 00:00:00 2001 From: Eric Dumazet Date: Wed, 2 Aug 2017 23:10:46 -0700 Subject: [PATCH] net: fix keepalive code vs TCP_FASTOPEN_CONNECT syzkaller was able to trigger a divide by 0 in TCP stack [1] Issue here is that keepalive timer needs to be updated to not attempt to send a probe if the connection setup was deferred using TCP_FASTOPEN_CONNECT socket option added in linux-4.11 [1] divide error: 0000 [#1] SMP CPU: 18 PID: 0 Comm: swapper/18 Not tainted task: ffff986f62f4b040 ti: ffff986f62fa2000 task.ti: ffff986f62fa2000 RIP: 0010:[] [] __tcp_select_window+0x8d/0x160 Call Trace: [] tcp_transmit_skb+0x11/0x20 [] tcp_xmit_probe_skb+0xc1/0xe0 [] tcp_write_wakeup+0x68/0x160 [] tcp_keepalive_timer+0x17b/0x230 [] call_timer_fn+0x39/0xf0 [] run_timer_softirq+0x1d7/0x280 [] __do_softirq+0xcb/0x257 [] irq_exit+0x9c/0xb0 [] smp_apic_timer_interrupt+0x6a/0x80 [] apic_timer_interrupt+0x7f/0x90 [] ? cpuidle_enter_state+0x13a/0x3b0 [] ? cpuidle_enter_state+0x11d/0x3b0 Tested: Following packetdrill no longer crashes the kernel `echo 0 >/proc/sys/net/ipv4/tcp_timestamps` // Cache warmup: send a Fast Open cookie request 0 socket(..., SOCK_STREAM, IPPROTO_TCP) = 3 +0 fcntl(3, F_SETFL, O_RDWR|O_NONBLOCK) = 0 +0 setsockopt(3, SOL_TCP, TCP_FASTOPEN_CONNECT, [1], 4) = 0 +0 connect(3, ..., ...) = -1 EINPROGRESS (Operation is now in progress) +0 > S 0:0(0) +.01 < S. 123:123(0) ack 1 win 14600 +0 > . 1:1(0) ack 1 +0 close(3) = 0 +0 > F. 1:1(0) ack 1 +0 < F. 1:1(0) ack 2 win 92 +0 > . 2:2(0) ack 2 +0 socket(..., SOCK_STREAM, IPPROTO_TCP) = 4 +0 fcntl(4, F_SETFL, O_RDWR|O_NONBLOCK) = 0 +0 setsockopt(4, SOL_TCP, TCP_FASTOPEN_CONNECT, [1], 4) = 0 +0 setsockopt(4, SOL_SOCKET, SO_KEEPALIVE, [1], 4) = 0 +.01 connect(4, ..., ...) = 0 +0 setsockopt(4, SOL_TCP, TCP_KEEPIDLE, [5], 4) = 0 +10 close(4) = 0 `echo 1 >/proc/sys/net/ipv4/tcp_timestamps` Fixes: 19f6d3f3c842 ("net/tcp-fastopen: Add new API support") Signed-off-by: Eric Dumazet Reported-by: Dmitry Vyukov Cc: Wei Wang Cc: Yuchung Cheng Signed-off-by: David S. Miller --- net/ipv4/tcp_timer.c | 3 ++- 1 file changed, 2 insertions(+), 1 deletion(-) diff --git a/net/ipv4/tcp_timer.c b/net/ipv4/tcp_timer.c index c0feeeef962a..e906014890b6 100644 --- a/net/ipv4/tcp_timer.c +++ b/net/ipv4/tcp_timer.c @@ -652,7 +652,8 @@ static void tcp_keepalive_timer (unsigned long data) goto death; } - if (!sock_flag(sk, SOCK_KEEPOPEN) || sk->sk_state == TCP_CLOSE) + if (!sock_flag(sk, SOCK_KEEPOPEN) || + ((1 << sk->sk_state) & (TCPF_CLOSE | TCPF_SYN_SENT))) goto out; elapsed = keepalive_time_when(tp); -- 2.20.1