netdev - Re: [PATCH net] mptcp: prevent BPF accessing lowat from a subflow socket.

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Date: Sat, 30 Mar 2024 10:53:05 +0100
From: Matthieu Baerts <matttbe@...nel.org>
To: Paolo Abeni <pabeni@...hat.com>, netdev@...r.kernel.org
Cc: Mat Martineau <martineau@...nel.org>, Geliang Tang <geliang@...nel.org>,
 "David S. Miller" <davem@...emloft.net>, Eric Dumazet <edumazet@...gle.com>,
 Jakub Kicinski <kuba@...nel.org>, mptcp@...ts.linux.dev, bpf@...r.kernel.org
Subject: Re: [PATCH net] mptcp: prevent BPF accessing lowat from a subflow
 socket.

Hi Paolo,

On 29/03/2024 19:50, Paolo Abeni wrote:
> Alexei reported the following splat:
> 
>  WARNING: CPU: 32 PID: 3276 at net/mptcp/subflow.c:1430 subflow_data_ready+0x147/0x1c0
>  Modules linked in: dummy bpf_testmod(O) [last unloaded: bpf_test_no_cfi(O)]
>  CPU: 32 PID: 3276 Comm: test_progs Tainted: GO       6.8.0-12873-g2c43c33bfd23
>  Call Trace:
>   <TASK>
>   mptcp_set_rcvlowat+0x79/0x1d0
>   sk_setsockopt+0x6c0/0x1540
>   __bpf_setsockopt+0x6f/0x90
>   bpf_sock_ops_setsockopt+0x3c/0x90
>   bpf_prog_509ce5db2c7f9981_bpf_test_sockopt_int+0xb4/0x11b
>   bpf_prog_dce07e362d941d2b_bpf_test_socket_sockopt+0x12b/0x132
>   bpf_prog_348c9b5faaf10092_skops_sockopt+0x954/0xe86
>   __cgroup_bpf_run_filter_sock_ops+0xbc/0x250
>   tcp_connect+0x879/0x1160
>   tcp_v6_connect+0x50c/0x870
>   mptcp_connect+0x129/0x280
>   __inet_stream_connect+0xce/0x370
>   inet_stream_connect+0x36/0x50
>   bpf_trampoline_6442491565+0x49/0xef
>   inet_stream_connect+0x5/0x50
>   __sys_connect+0x63/0x90
>   __x64_sys_connect+0x14/0x20
> 
> The root cause of the issue is that bpf allows accessing mptcp-level
> proto_ops from a tcp subflow scope.
> 
> Fix the issue detecting the problematic call and preventing any action.

Thank you for having looked at that! The patch looks good to me as well:

Reviewed-by: Matthieu Baerts (NGI0) <matttbe@...nel.org>

FYI, the patch was also OK for our CI, but we don't run all BPF tests.

Cheers,
Matt
-- 
Sponsored by the NGI0 Core fund.