netdev - Re: [PATCH net] tcp: ensure sk_showdown is 0 for listening sockets

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Message-ID: <CANn89i+zxB9g7n3JWXd8B-kkSkfRWfb7mOQcQi+mMLs6U-n5tQ@mail.gmail.com>
Date: Mon, 20 May 2024 15:46:44 +0200
From: Eric Dumazet <edumazet@...gle.com>
To: Paolo Abeni <pabeni@...hat.com>
Cc: netdev@...r.kernel.org, "David S. Miller" <davem@...emloft.net>, 
	David Ahern <dsahern@...nel.org>, Jakub Kicinski <kuba@...nel.org>, 
	Christoph Paasch <cpaasch@...le.com>
Subject: Re: [PATCH net] tcp: ensure sk_showdown is 0 for listening sockets

On Mon, May 20, 2024 at 12:05 PM Paolo Abeni <pabeni@...hat.com> wrote:
>
> Christoph reported the following splat:
>
> WARNING: CPU: 1 PID: 772 at net/ipv4/af_inet.c:761 __inet_accept+0x1f4/0x4a0
> Modules linked in:
> CPU: 1 PID: 772 Comm: syz-executor510 Not tainted 6.9.0-rc7-g7da7119fe22b #56
> Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.11.0-2.el7 04/01/2014
> RIP: 0010:__inet_accept+0x1f4/0x4a0 net/ipv4/af_inet.c:759
> Code: 04 38 84 c0 0f 85 87 00 00 00 41 c7 04 24 03 00 00 00 48 83 c4 10 5b 41 5c 41 5d 41 5e 41 5f 5d c3 cc cc cc cc e8 ec b7 da fd <0f> 0b e9 7f fe ff ff e8 e0 b7 da fd 0f 0b e9 fe fe ff ff 89 d9 80
> RSP: 0018:ffffc90000c2fc58 EFLAGS: 00010293
> RAX: ffffffff836bdd14 RBX: 0000000000000000 RCX: ffff888104668000
> RDX: 0000000000000000 RSI: 0000000000000000 RDI: 0000000000000000
> RBP: dffffc0000000000 R08: ffffffff836bdb89 R09: fffff52000185f64
> R10: dffffc0000000000 R11: fffff52000185f64 R12: dffffc0000000000
> R13: 1ffff92000185f98 R14: ffff88810754d880 R15: ffff8881007b7800
> FS:  000000001c772880(0000) GS:ffff88811b280000(0000) knlGS:0000000000000000
> CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
> CR2: 00007fb9fcf2e178 CR3: 00000001045d2002 CR4: 0000000000770ef0
> DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
> DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
> PKRU: 55555554
> Call Trace:
>  <TASK>
>  inet_accept+0x138/0x1d0 net/ipv4/af_inet.c:786
>  do_accept+0x435/0x620 net/socket.c:1929
>  __sys_accept4_file net/socket.c:1969 [inline]
>  __sys_accept4+0x9b/0x110 net/socket.c:1999
>  __do_sys_accept net/socket.c:2016 [inline]
>  __se_sys_accept net/socket.c:2013 [inline]
>  __x64_sys_accept+0x7d/0x90 net/socket.c:2013
>  do_syscall_x64 arch/x86/entry/common.c:52 [inline]
>  do_syscall_64+0x58/0x100 arch/x86/entry/common.c:83
>  entry_SYSCALL_64_after_hwframe+0x76/0x7e
> RIP: 0033:0x4315f9
> Code: fd ff 48 81 c4 80 00 00 00 e9 f1 fe ff ff 0f 1f 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 0f 83 ab b4 fd ff c3 66 2e 0f 1f 84 00 00 00 00
> RSP: 002b:00007ffdb26d9c78 EFLAGS: 00000246 ORIG_RAX: 000000000000002b
> RAX: ffffffffffffffda RBX: 0000000000400300 RCX: 00000000004315f9
> RDX: 0000000000000000 RSI: 0000000000000000 RDI: 0000000000000004
> RBP: 00000000006e1018 R08: 0000000000400300 R09: 0000000000400300
> R10: 0000000000400300 R11: 0000000000000246 R12: 0000000000000000
> R13: 000000000040cdf0 R14: 000000000040ce80 R15: 0000000000000055
>  </TASK>
>
> Listener sockets are supposed to have a zero sk_shutdown, as the
> accepted children will inherit such field.
>
> Invoking shutdown() before entering the listener status allows
> violating the above constraint.
>
> After commit 94062790aedb ("tcp: defer shutdown(SEND_SHUTDOWN) for
> TCP_SYN_RECV sockets"), the above causes the child to reach the accept
> syscall in FIN_WAIT1 status.
>
> Address the issue explicitly by clearing sk_shutdown at listen time.
>
> Reported-by: Christoph Paasch <cpaasch@...le.com>
> Closes: https://github.com/multipath-tcp/mptcp_net-next/issues/490
> Fixes: 1da177e4c3fu ("Linux-2.6.12-rc2")
> Signed-off-by: Paolo Abeni <pabeni@...hat.com>
> ---
> Note: the issue above reports an MPTCP reproducer, but I can reproduce
> the issue even using plain TCP sockets only.
> ---
>  net/ipv4/inet_connection_sock.c | 2 ++
>  1 file changed, 2 insertions(+)
>
> diff --git a/net/ipv4/inet_connection_sock.c b/net/ipv4/inet_connection_sock.c
> index 3b38610958ee..dab723fea0cc 100644
> --- a/net/ipv4/inet_connection_sock.c
> +++ b/net/ipv4/inet_connection_sock.c
> @@ -1269,6 +1269,8 @@ int inet_csk_listen_start(struct sock *sk)
>
>         reqsk_queue_alloc(&icsk->icsk_accept_queue);
>
> +       /* closed sockets can have non zero sk_shutdown */
> +       WRITE_ONCE(sk->sk_shutdown, 0);

Hi Paolo.

I am unsure about your patch, I had an internal syzbot report about
this before going OOO for a few days,
and my first reaction was to change the WARN in inet_accept().

Perhaps some applications are relying on calling shutdown() before listen()...