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Thu, 18 Dec 2025 14:21:30 -0800 (PST) Received: from [192.168.1.150] ([198.8.77.157]) by smtp.gmail.com with ESMTPSA id 46e09a7af769-7cc667ebe98sm472901a34.21.2025.12.18.14.21.29 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Thu, 18 Dec 2025 14:21:29 -0800 (PST) Message-ID: <07adc0c2-2c3b-4d08-8af1-1c466a40b6a8@kernel.dk> Date: Thu, 18 Dec 2025 15:21:28 -0700 Precedence: bulk X-Mailing-List: io-uring@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Content-Language: en-US To: netdev Cc: io-uring , Jakub Kicinski , Willem de Bruijn , Kuniyuki Iwashima , Julian Orth From: Jens Axboe Subject: [PATCH v2] af_unix: don't post cmsg for SO_INQ unless explicitly asked for Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit 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: df30285b3670 ("af_unix: Introduce SO_INQ.") Reported-by: Julian Orth Link: https://github.com/axboe/liburing/issues/1509 Signed-off-by: Jens Axboe --- V2: - Unify logic with tcp - Squash the two patches into one diff --git a/net/unix/af_unix.c b/net/unix/af_unix.c index 55cdebfa0da0..a7ca74653d94 100644 --- a/net/unix/af_unix.c +++ b/net/unix/af_unix.c @@ -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 @@ -3088,10 +3092,11 @@ 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); - put_cmsg(msg, SOL_SOCKET, SCM_INQ, - sizeof(msg->msg_inq), &msg->msg_inq); + if (do_cmsg) + put_cmsg(msg, SOL_SOCKET, SCM_INQ, + sizeof(msg->msg_inq), &msg->msg_inq); } } else { scm_destroy(&scm); -- Jens Axboe