Commit 4d144297 authored Dec 18, 2025 by Jens Axboe Committed by Paolo Abeni Dec 28, 2025

af_unix: don't post cmsg for SO_INQ unless explicitly asked for



A previous commit added SO_INQ support for AF_UNIX (SOCK_STREAM), but it
posts a SCM_INQ cmsg even if just msg->msg_get_inq is set. This is
incorrect, as ->msg_get_inq is just the caller asking for the remainder
to be passed back in msg->msg_inq, it has nothing to do with cmsg. The
original commit states that this is done to make sockets
io_uring-friendly", but it's actually incorrect as io_uring doesn't use
cmsg headers internally at all, and it's actively wrong as this means
that cmsg's are always posted if someone does recvmsg via io_uring.

Fix that up by only posting a cmsg if u->recvmsg_inq is set.

Additionally, mirror how TCP handles inquiry handling in that it should
only be done for a successful return. This makes the logic for the two
identical.

Cc: stable@vger.kernel.org
Fixes: df30285b ("af_unix: Introduce SO_INQ.")
Reported-by: Julian Orth <ju.orth@gmail.com>
Link: https://github.com/axboe/liburing/issues/1509


Signed-off-by: Jens Axboe <axboe@kernel.dk>
Reviewed-by: Willem de Bruijn <willemb@google.com>
Link: https://patch.msgid.link/07adc0c2-2c3b-4d08-8af1-1c466a40b6a8@kernel.dk


Signed-off-by: Paolo Abeni <pabeni@redhat.com>

parent 3387a7ad

net/unix/af_unix.c

+8 −3

Original line number	Diff line number	Diff line
		@@ -2904,6 +2904,7 @@ static int unix_stream_read_generic(struct unix_stream_read_state *state,
		unsigned int last_len;
		struct unix_sock *u;
		int copied = 0;
		bool do_cmsg;
		int err = 0;
		long timeo;
		int target;
		@@ -2929,6 +2930,9 @@ static int unix_stream_read_generic(struct unix_stream_read_state *state,

		u = unix_sk(sk);

		do_cmsg = READ_ONCE(u->recvmsg_inq);
		if (do_cmsg)
		msg->msg_get_inq = 1;
		redo:
		/* Lock the socket to prevent queue disordering
		* while sleeps in memcpy_tomsg
		@@ -3088,8 +3092,9 @@ static int unix_stream_read_generic(struct unix_stream_read_state *state,
		if (msg) {
		scm_recv_unix(sock, msg, &scm, flags);

		if (READ_ONCE(u->recvmsg_inq) \|\| msg->msg_get_inq) {
		if (msg->msg_get_inq && (copied ?: err) >= 0) {
		msg->msg_inq = READ_ONCE(u->inq_len);
		if (do_cmsg)
		put_cmsg(msg, SOL_SOCKET, SCM_INQ,
		sizeof(msg->msg_inq), &msg->msg_inq);
		}