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 13:02:46 -0700
From: Rao Shoaib <rao.shoaib@...cle.com>
To: Jakub Sitnicki <jakub@...udflare.com>, 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,
        Cong Wang <cong.wang@...edance.com>
Subject: Re: [PATCH bpf v2] af_unix: Disable MSG_OOB handling for sockets in
 sockmap/sockhash


On 6/24/24 07:15, Jakub Sitnicki wrote:
> 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 an OOB packet is moved between sockets, `oob_skb` is left outdated.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://urldefense.com/v3/__https://git.kernel.org/pub/scm/linux/kernel/git/bpf/bpf.git/tree/tools/testing/selftests/bpf/prog_tests/sockmap_listen.c*n1884__;Iw!!ACWV5N9M2RV99hQ!K-FmI13Wd7NvcxnWmsgoiqJtOSe4b4ydFXIvMs4JFOWWesx2LLtlg8LG22_Fd49e67cl50SdkB4JFg4-$ 

I would like to understand why this is not an issue for TCP as we try to
mimic TCP OOB behavior for AF_UNIX sockets. However, I am out of the
office till July 8th and can only look at the issue after my return.

Shoaib