netdev - Re: [PATCH v2 net 01/15] af_unix: Set sk->sk_state under unix_state

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Date: Wed, 19 Jun 2024 12:19:30 -0700
From: Kuniyuki Iwashima <kuniyu@...zon.com>
To: <mhal@...x.co>
CC: <cong.wang@...edance.com>, <davem@...emloft.net>, <edumazet@...gle.com>,
	<kuba@...nel.org>, <kuni1840@...il.com>, <kuniyu@...zon.com>,
	<netdev@...r.kernel.org>, <pabeni@...hat.com>
Subject: Re: [PATCH v2 net 01/15] af_unix: Set sk->sk_state under unix_state_lock() for truly disconencted peer.

From: Michal Luczaj <mhal@...x.co>
Date: Wed, 19 Jun 2024 20:14:48 +0200
> On 6/17/24 20:21, Kuniyuki Iwashima wrote:
> > From: Michal Luczaj <mhal@...x.co>
> > Date: Mon, 17 Jun 2024 01:28:52 +0200
> >> (...)
> >> Another AF_UNIX sockmap issue is with OOB. When OOB packet is sent, skb is
> >> added to recv queue, but also u->oob_skb is set. Here's the problem: when
> >> this skb goes through bpf_sk_redirect_map() and is moved between socks,
> >> oob_skb remains set on the original sock.
> > 
> > Good catch!
> > 
> >>
> >> [   23.688994] WARNING: CPU: 2 PID: 993 at net/unix/garbage.c:351 unix_collect_queue+0x6c/0xb0
> >> [   23.689019] CPU: 2 PID: 993 Comm: kworker/u32:13 Not tainted 6.10.0-rc2+ #137
> >> [   23.689021] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS Arch Linux 1.16.3-1-1 04/01/2014
> >> [   23.689024] Workqueue: events_unbound __unix_gc
> >> [   23.689027] RIP: 0010:unix_collect_queue+0x6c/0xb0
> >>
> >> I wanted to write a patch, but then I realized I'm not sure what's the
> >> expected behaviour. Should the oob_skb setting follow to the skb's new sock
> >> or should it be dropped (similarly to what is happening today with
> >> scm_fp_list, i.e. redirect strips inflights)?
> > 
> > The former will require large refactoring as we need to check if the
> > redirect happens for BPF_F_INGRESS and if the redirected sk is also
> > SOCK_STREAM etc.
> > 
> > So, I'd go with the latter.  Probably we can check if skb is u->oob_skb
> > and drop OOB data and retry next in unix_stream_read_skb(), and forbid
> > MSG_OOB in unix_bpf_recvmsg().
> > (...)
> 
> Yeah, sounds reasonable. I'm just not sure I understand the retry part. For
> each skb_queue_tail() there's one ->sk_data_ready() (which does
> ->read_skb()). Why bother with a retry?

Exactly.


> 
> This is what I was thinking:
>

When you post it, please make sure to CC bpf@ and sockmap maintainers too.