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an OOB packet is moved between sockets, `oob_skb` is left outdated.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 <redacted>
Fixes: 314001f0bf92 ("af_unix: Add OOB support")
Signed-off-by: Michal Luczaj <redacted>
---

[+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