netdev - Re: [PATCH net] vsock/bpf: Handle EINTR connect() racing against sockmap update

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Message-ID: <24efb98c-d6ba-42c2-91b7-71b969179aff@rbox.co>
Date: Fri, 14 Mar 2025 16:29:03 +0100
From: Michal Luczaj <mhal@...x.co>
To: John Fastabend <john.fastabend@...il.com>
Cc: Stefano Garzarella <sgarzare@...hat.com>,
 "David S. Miller" <davem@...emloft.net>, Eric Dumazet <edumazet@...gle.com>,
 Jakub Kicinski <kuba@...nel.org>, Paolo Abeni <pabeni@...hat.com>,
 Simon Horman <horms@...nel.org>,
 Bobby Eshleman <bobby.eshleman@...edance.com>,
 "Michael S. Tsirkin" <mst@...hat.com>, netdev@...r.kernel.org,
 bpf@...r.kernel.org
Subject: Re: [PATCH net] vsock/bpf: Handle EINTR connect() racing against
 sockmap update

On 3/11/25 17:23, John Fastabend wrote:
> On 2025-03-07 10:27:50, Michal Luczaj wrote:
>> Signal delivered during connect() may result in a disconnect of an already
>> TCP_ESTABLISHED socket. Problem is that such established socket might have
>> been placed in a sockmap before the connection was closed. We end up with a
>> SS_UNCONNECTED vsock in a sockmap. And this, combined with the ability to
>> reassign (unconnected) vsock's transport to NULL, breaks the sockmap
>> contract. As manifested by WARN_ON_ONCE.
>>
>> Ensure the socket does not stay in sockmap.
>>
>> WARNING: CPU: 10 PID: 1310 at net/vmw_vsock/vsock_bpf.c:90 vsock_bpf_recvmsg+0xb4b/0xdf0
>> CPU: 10 UID: 0 PID: 1310 Comm: a.out Tainted: G        W          6.14.0-rc4+
>>  sock_recvmsg+0x1b2/0x220
>>  __sys_recvfrom+0x190/0x270
>>  __x64_sys_recvfrom+0xdc/0x1b0
>>  do_syscall_64+0x93/0x1b0
>>  entry_SYSCALL_64_after_hwframe+0x76/0x7e
>>
>> Fixes: 634f1a7110b4 ("vsock: support sockmap")
>> Signed-off-by: Michal Luczaj <mhal@...x.co>
> 
> Hi Michal,
> 
> Unhashing the socket to stop any references from sockmap side if the
> sock is being put into CLOSING state makes sense to me. Was there
> another v2 somewhere? I didn't see it in my inbox or I missed it.
> I think you mentioned more fixes were needed.

Great, thanks for checking. I was worried I might be missing some
subtleties of sock_map_unhash() not calling `sk_psock_stop(psock)` nor
`cancel_delayed_work_sync(&psock->work)`. Especially since user still has
socket descriptor open and can play with such "unhashed" socket.

I've just sent v2: https://lore.kernel.org/netdev/20250314-vsock-trans-signal-race-v2-0-421a41f60f42@rbox.co/

Repro is adapted to sockmap_basic. And to answer your question from
another thread: test triggers warning in a second. Currently timeout is 2s.
I'm not sure how useful it may be for other families, but let me know if
you'd rather have it somehow more generic.

Thanks,
Michal