From bca44926fe614f52009b53d8d8b4e80ff44da057 Mon Sep 17 00:00:00 2001 From: Eric Dumazet Date: Mon, 14 May 2018 21:14:26 -0700 Subject: [PATCH] tcp: purge write queue in tcp_connect_init() [ Upstream commit 7f582b248d0a86bae5788c548d7bb5bca6f7691a ] syzkaller found a reliable way to crash the host, hitting a BUG() in __tcp_retransmit_skb() Malicous MSG_FASTOPEN is the root cause. We need to purge write queue in tcp_connect_init() at the point we init snd_una/write_seq. This patch also replaces the BUG() by a less intrusive WARN_ON_ONCE() kernel BUG at net/ipv4/tcp_output.c:2837! invalid opcode: 0000 [#1] SMP KASAN Dumping ftrace buffer: (ftrace buffer empty) Modules linked in: CPU: 0 PID: 5276 Comm: syz-executor0 Not tainted 4.17.0-rc3+ #51 Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011 RIP: 0010:__tcp_retransmit_skb+0x2992/0x2eb0 net/ipv4/tcp_output.c:2837 RSP: 0000:ffff8801dae06ff8 EFLAGS: 00010206 RAX: ffff8801b9fe61c0 RBX: 00000000ffc18a16 RCX: ffffffff864e1a49 RDX: 0000000000000100 RSI: ffffffff864e2e12 RDI: 0000000000000005 RBP: ffff8801dae073a0 R08: ffff8801b9fe61c0 R09: ffffed0039c40dd2 R10: ffffed0039c40dd2 R11: ffff8801ce206e93 R12: 00000000421eeaad R13: ffff8801ce206d4e R14: ffff8801ce206cc0 R15: ffff8801cd4f4a80 FS: 0000000000000000(0000) GS:ffff8801dae00000(0063) knlGS:00000000096bc900 CS: 0010 DS: 002b ES: 002b CR0: 0000000080050033 CR2: 0000000020000000 CR3: 00000001c47b6000 CR4: 00000000001406f0 DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000 DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400 Call Trace: tcp_retransmit_skb+0x2e/0x250 net/ipv4/tcp_output.c:2923 tcp_retransmit_timer+0xc50/0x3060 net/ipv4/tcp_timer.c:488 tcp_write_timer_handler+0x339/0x960 net/ipv4/tcp_timer.c:573 tcp_write_timer+0x111/0x1d0 net/ipv4/tcp_timer.c:593 call_timer_fn+0x230/0x940 kernel/time/timer.c:1326 expire_timers kernel/time/timer.c:1363 [inline] __run_timers+0x79e/0xc50 kernel/time/timer.c:1666 run_timer_softirq+0x4c/0x70 kernel/time/timer.c:1692 __do_softirq+0x2e0/0xaf5 kernel/softirq.c:285 invoke_softirq kernel/softirq.c:365 [inline] irq_exit+0x1d1/0x200 kernel/softirq.c:405 exiting_irq arch/x86/include/asm/apic.h:525 [inline] smp_apic_timer_interrupt+0x17e/0x710 arch/x86/kernel/apic/apic.c:1052 apic_timer_interrupt+0xf/0x20 arch/x86/entry/entry_64.S:863 Change-Id: Iee222f98268d346c9d4c09950206e2f97ec6ec0f Fixes: cf60af03ca4e ("net-tcp: Fast Open client - sendmsg(MSG_FASTOPEN)") Signed-off-by: Eric Dumazet Cc: Yuchung Cheng Cc: Neal Cardwell Reported-by: syzbot Acked-by: Neal Cardwell Signed-off-by: David S. Miller Signed-off-by: Greg Kroah-Hartman --- net/ipv4/tcp_output.c | 7 +++++-- 1 file changed, 5 insertions(+), 2 deletions(-) diff --git a/net/ipv4/tcp_output.c b/net/ipv4/tcp_output.c index 5f7aaadb3a10..7d18f2e45e97 100644 --- a/net/ipv4/tcp_output.c +++ b/net/ipv4/tcp_output.c @@ -2814,8 +2814,10 @@ int __tcp_retransmit_skb(struct sock *sk, struct sk_buff *skb, int segs) return -EBUSY; if (before(TCP_SKB_CB(skb)->seq, tp->snd_una)) { - if (before(TCP_SKB_CB(skb)->end_seq, tp->snd_una)) - BUG(); + if (unlikely(before(TCP_SKB_CB(skb)->end_seq, tp->snd_una))) { + WARN_ON_ONCE(1); + return -EINVAL; + } if (tcp_trim_head(sk, skb, tp->snd_una - TCP_SKB_CB(skb)->seq)) return -ENOMEM; } @@ -3312,6 +3314,7 @@ static void tcp_connect_init(struct sock *sk) sock_reset_flag(sk, SOCK_DONE); tp->snd_wnd = 0; tcp_init_wl(tp, 0); + tcp_write_queue_purge(sk); tp->snd_una = tp->write_seq; tp->snd_sml = tp->write_seq; tp->snd_up = tp->write_seq; -- 2.20.1