netdev - Re: [PATCH v1 net 1/4] af_unix: Fix data-races around user->unix

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Date: Sat, 2 Sep 2023 08:39:37 +0200
From: Eric Dumazet <edumazet@...gle.com>
To: Kuniyuki Iwashima <kuniyu@...zon.com>
Cc: "David S. Miller" <davem@...emloft.net>, Jakub Kicinski <kuba@...nel.org>, 
	Paolo Abeni <pabeni@...hat.com>, Kuniyuki Iwashima <kuni1840@...il.com>, netdev@...r.kernel.org, 
	syzkaller <syzkaller@...glegroups.com>, Willy Tarreau <w@....eu>
Subject: Re: [PATCH v1 net 1/4] af_unix: Fix data-races around user->unix_inflight.

On Sat, Sep 2, 2023 at 2:28 AM Kuniyuki Iwashima <kuniyu@...zon.com> wrote:
>
> user->unix_inflight is changed under spin_lock(unix_gc_lock),
> but too_many_unix_fds() reads it locklessly.
>
> Let's annotate the write/read accesses to user->unix_inflight.
>
> BUG: KCSAN: data-race in unix_attach_fds / unix_inflight
>
> write to 0xffffffff8546f2d0 of 8 bytes by task 44798 on cpu 1:
>  unix_inflight+0x157/0x180 net/unix/scm.c:66
>  unix_attach_fds+0x147/0x1e0 net/unix/scm.c:123
>  unix_scm_to_skb net/unix/af_unix.c:1827 [inline]
>  unix_dgram_sendmsg+0x46a/0x14f0 net/unix/af_unix.c:1950
>  unix_seqpacket_sendmsg net/unix/af_unix.c:2308 [inline]
>  unix_seqpacket_sendmsg+0xba/0x130 net/unix/af_unix.c:2292
>  sock_sendmsg_nosec net/socket.c:725 [inline]
>  sock_sendmsg+0x148/0x160 net/socket.c:748
>  ____sys_sendmsg+0x4e4/0x610 net/socket.c:2494
>  ___sys_sendmsg+0xc6/0x140 net/socket.c:2548
>  __sys_sendmsg+0x94/0x140 net/socket.c:2577
>  __do_sys_sendmsg net/socket.c:2586 [inline]
>  __se_sys_sendmsg net/socket.c:2584 [inline]
>  __x64_sys_sendmsg+0x45/0x50 net/socket.c:2584
>  do_syscall_x64 arch/x86/entry/common.c:50 [inline]
>  do_syscall_64+0x3b/0x90 arch/x86/entry/common.c:80
>  entry_SYSCALL_64_after_hwframe+0x6e/0xd8
>
> read to 0xffffffff8546f2d0 of 8 bytes by task 44814 on cpu 0:
>  too_many_unix_fds net/unix/scm.c:101 [inline]
>  unix_attach_fds+0x54/0x1e0 net/unix/scm.c:110
>  unix_scm_to_skb net/unix/af_unix.c:1827 [inline]
>  unix_dgram_sendmsg+0x46a/0x14f0 net/unix/af_unix.c:1950
>  unix_seqpacket_sendmsg net/unix/af_unix.c:2308 [inline]
>  unix_seqpacket_sendmsg+0xba/0x130 net/unix/af_unix.c:2292
>  sock_sendmsg_nosec net/socket.c:725 [inline]
>  sock_sendmsg+0x148/0x160 net/socket.c:748
>  ____sys_sendmsg+0x4e4/0x610 net/socket.c:2494
>  ___sys_sendmsg+0xc6/0x140 net/socket.c:2548
>  __sys_sendmsg+0x94/0x140 net/socket.c:2577
>  __do_sys_sendmsg net/socket.c:2586 [inline]
>  __se_sys_sendmsg net/socket.c:2584 [inline]
>  __x64_sys_sendmsg+0x45/0x50 net/socket.c:2584
>  do_syscall_x64 arch/x86/entry/common.c:50 [inline]
>  do_syscall_64+0x3b/0x90 arch/x86/entry/common.c:80
>  entry_SYSCALL_64_after_hwframe+0x6e/0xd8
>
> value changed: 0x000000000000000c -> 0x000000000000000d
>
> Reported by Kernel Concurrency Sanitizer on:
> CPU: 0 PID: 44814 Comm: systemd-coredum Not tainted 6.4.0-11989-g6843306689af #6
> Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS rel-1.16.0-0-gd239552ce722-prebuilt.qemu.org 04/01/2014
>
> Fixes: 712f4aad406b ("unix: properly account for FDs passed over unix sockets")
> Reported-by: syzkaller <syzkaller@...glegroups.com>
> Signed-off-by: Kuniyuki Iwashima <kuniyu@...zon.com>

Reviewed-by: Eric Dumazet <edumazet@...gle.com>