| From 11825765291a93d8e7f44230da67b9f607c777bf Mon Sep 17 00:00:00 2001 |
| From: Eric Dumazet <edumazet@google.com> |
| Date: Fri, 27 May 2022 14:28:29 -0700 |
| Subject: tcp: fix tcp_mtup_probe_success vs wrong snd_cwnd |
| |
| From: Eric Dumazet <edumazet@google.com> |
| |
| commit 11825765291a93d8e7f44230da67b9f607c777bf upstream. |
| |
| syzbot got a new report [1] finally pointing to a very old bug, |
| added in initial support for MTU probing. |
| |
| tcp_mtu_probe() has checks about starting an MTU probe if |
| tcp_snd_cwnd(tp) >= 11. |
| |
| But nothing prevents tcp_snd_cwnd(tp) to be reduced later |
| and before the MTU probe succeeds. |
| |
| This bug would lead to potential zero-divides. |
| |
| Debugging added in commit 40570375356c ("tcp: add accessors |
| to read/set tp->snd_cwnd") has paid off :) |
| |
| While we are at it, address potential overflows in this code. |
| |
| [1] |
| WARNING: CPU: 1 PID: 14132 at include/net/tcp.h:1219 tcp_mtup_probe_success+0x366/0x570 net/ipv4/tcp_input.c:2712 |
| Modules linked in: |
| CPU: 1 PID: 14132 Comm: syz-executor.2 Not tainted 5.18.0-syzkaller-07857-gbabf0bb978e3 #0 |
| Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011 |
| RIP: 0010:tcp_snd_cwnd_set include/net/tcp.h:1219 [inline] |
| RIP: 0010:tcp_mtup_probe_success+0x366/0x570 net/ipv4/tcp_input.c:2712 |
| Code: 74 08 48 89 ef e8 da 80 17 f9 48 8b 45 00 65 48 ff 80 80 03 00 00 48 83 c4 30 5b 41 5c 41 5d 41 5e 41 5f 5d c3 e8 aa b0 c5 f8 <0f> 0b e9 16 fe ff ff 48 8b 4c 24 08 80 e1 07 38 c1 0f 8c c7 fc ff |
| RSP: 0018:ffffc900079e70f8 EFLAGS: 00010287 |
| RAX: ffffffff88c0f7f6 RBX: ffff8880756e7a80 RCX: 0000000000040000 |
| RDX: ffffc9000c6c4000 RSI: 0000000000031f9e RDI: 0000000000031f9f |
| RBP: 0000000000000000 R08: ffffffff88c0f606 R09: ffffc900079e7520 |
| R10: ffffed101011226d R11: 1ffff1101011226c R12: 1ffff1100eadcf50 |
| R13: ffff8880756e72c0 R14: 1ffff1100eadcf89 R15: dffffc0000000000 |
| FS: 00007f643236e700(0000) GS:ffff8880b9b00000(0000) knlGS:0000000000000000 |
| CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 |
| CR2: 00007f1ab3f1e2a0 CR3: 0000000064fe7000 CR4: 00000000003506e0 |
| DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000 |
| DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400 |
| Call Trace: |
| <TASK> |
| tcp_clean_rtx_queue+0x223a/0x2da0 net/ipv4/tcp_input.c:3356 |
| tcp_ack+0x1962/0x3c90 net/ipv4/tcp_input.c:3861 |
| tcp_rcv_established+0x7c8/0x1ac0 net/ipv4/tcp_input.c:5973 |
| tcp_v6_do_rcv+0x57b/0x1210 net/ipv6/tcp_ipv6.c:1476 |
| sk_backlog_rcv include/net/sock.h:1061 [inline] |
| __release_sock+0x1d8/0x4c0 net/core/sock.c:2849 |
| release_sock+0x5d/0x1c0 net/core/sock.c:3404 |
| sk_stream_wait_memory+0x700/0xdc0 net/core/stream.c:145 |
| tcp_sendmsg_locked+0x111d/0x3fc0 net/ipv4/tcp.c:1410 |
| tcp_sendmsg+0x2c/0x40 net/ipv4/tcp.c:1448 |
| sock_sendmsg_nosec net/socket.c:714 [inline] |
| sock_sendmsg net/socket.c:734 [inline] |
| __sys_sendto+0x439/0x5c0 net/socket.c:2119 |
| __do_sys_sendto net/socket.c:2131 [inline] |
| __se_sys_sendto net/socket.c:2127 [inline] |
| __x64_sys_sendto+0xda/0xf0 net/socket.c:2127 |
| do_syscall_x64 arch/x86/entry/common.c:50 [inline] |
| do_syscall_64+0x2b/0x70 arch/x86/entry/common.c:80 |
| entry_SYSCALL_64_after_hwframe+0x46/0xb0 |
| RIP: 0033:0x7f6431289109 |
| Code: ff ff c3 66 2e 0f 1f 84 00 00 00 00 00 0f 1f 40 00 48 89 f8 48 89 f7 48 89 d6 48 89 ca 4d 89 c2 4d 89 c8 4c 8b 4c 24 08 0f 05 <48> 3d 01 f0 ff ff 73 01 c3 48 c7 c1 b8 ff ff ff f7 d8 64 89 01 48 |
| RSP: 002b:00007f643236e168 EFLAGS: 00000246 ORIG_RAX: 000000000000002c |
| RAX: ffffffffffffffda RBX: 00007f643139c100 RCX: 00007f6431289109 |
| RDX: 00000000d0d0c2ac RSI: 0000000020000080 RDI: 000000000000000a |
| RBP: 00007f64312e308d R08: 0000000000000000 R09: 0000000000000000 |
| R10: 0000000000000001 R11: 0000000000000246 R12: 0000000000000000 |
| R13: 00007fff372533af R14: 00007f643236e300 R15: 0000000000022000 |
| |
| Fixes: 5d424d5a674f ("[TCP]: MTU probing") |
| Signed-off-by: Eric Dumazet <edumazet@google.com> |
| Reported-by: syzbot <syzkaller@googlegroups.com> |
| Acked-by: Yuchung Cheng <ycheng@google.com> |
| Acked-by: Neal Cardwell <ncardwell@google.com> |
| Signed-off-by: David S. Miller <davem@davemloft.net> |
| Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org> |
| --- |
| net/ipv4/tcp_input.c | 11 +++++++---- |
| 1 file changed, 7 insertions(+), 4 deletions(-) |
| |
| --- a/net/ipv4/tcp_input.c |
| +++ b/net/ipv4/tcp_input.c |
| @@ -2663,12 +2663,15 @@ static void tcp_mtup_probe_success(struc |
| { |
| struct tcp_sock *tp = tcp_sk(sk); |
| struct inet_connection_sock *icsk = inet_csk(sk); |
| + u64 val; |
| |
| - /* FIXME: breaks with very large cwnd */ |
| tp->prior_ssthresh = tcp_current_ssthresh(sk); |
| - tp->snd_cwnd = tp->snd_cwnd * |
| - tcp_mss_to_mtu(sk, tp->mss_cache) / |
| - icsk->icsk_mtup.probe_size; |
| + |
| + val = (u64)tp->snd_cwnd * tcp_mss_to_mtu(sk, tp->mss_cache); |
| + do_div(val, icsk->icsk_mtup.probe_size); |
| + WARN_ON_ONCE((u32)val != val); |
| + tp->snd_cwnd = max_t(u32, 1U, val); |
| + |
| tp->snd_cwnd_cnt = 0; |
| tp->snd_cwnd_stamp = tcp_time_stamp; |
| tp->snd_ssthresh = tcp_current_ssthresh(sk); |