netdev - Re: [PATCH bpf v2] af_unix: Disable MSG_OOB handling for sockets in sockmap/sockhash

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Date: Mon, 24 Jun 2024 16:15:49 +0200
From: Jakub Sitnicki <jakub@...udflare.com>
To: Michal Luczaj <mhal@...x.co>
Cc: netdev@...r.kernel.org,  bpf@...r.kernel.org,  davem@...emloft.net,
  edumazet@...gle.com,  kuba@...nel.org,  pabeni@...hat.com,
  john.fastabend@...il.com,  kuniyu@...zon.com,  Rao.Shoaib@...cle.com,
 Cong Wang <cong.wang@...edance.com>
Subject: Re: [PATCH bpf v2] af_unix: Disable MSG_OOB handling for sockets in
 sockmap/sockhash

On Sun, Jun 23, 2024 at 12:25 AM +02, Michal Luczaj wrote:
> AF_UNIX socket tracks the most recent OOB packet (in its receive queue)
> with an `oob_skb` pointer. BPF redirecting does not account for that: when
> an OOB packet is moved between sockets, `oob_skb` is left outdated. This
> results in a single skb that may be accessed from two different sockets.
>
> Take the easy way out: silently drop MSG_OOB data targeting any socket that
> is in a sockmap or a sockhash. Note that such silent drop is akin to the
> fate of redirected skb's scm_fp_list (SCM_RIGHTS, SCM_CREDENTIALS).
>
> For symmetry, forbid MSG_OOB in unix_bpf_recvmsg().
>
> Suggested-by: Kuniyuki Iwashima <kuniyu@...zon.com>
> Fixes: 314001f0bf92 ("af_unix: Add OOB support")
> Signed-off-by: Michal Luczaj <mhal@...x.co>
> ---

[+CC Cong who authored ->read_skb]

I'm guessing you have a test program that you're developing the fix
against. Would you like to extend the test case for sockmap redirect
from unix stream [1] to incorporate it?

Sadly unix_inet_redir_to_connected needs a fix first because it
hardcodes sotype to SOCK_DGRAM.

[1] https://git.kernel.org/pub/scm/linux/kernel/git/bpf/bpf.git/tree/tools/testing/selftests/bpf/prog_tests/sockmap_listen.c#n1884