[PATCH] io_uring/net: disable partial retries for recvmsg with cmsg

[Jens Axboe <axboe@kernel.dk>]

We cannot sanely handle partial retries for recvmsg if we have cmsg
attached. If we don't, then we'd just be overwriting the initial cmsg
header on retries. Alternatively we could increment and handle this
appropriately, but it doesn't seem worth the complication.

Link: https://lore.kernel.org/io-uring/0b0d4411-c8fd-4272-770b-e030af6919a0@kernel.dk/
Cc: stable@vger.kernel.org # 5.10+
Reported-by: Stefan Metzmacher <metze@samba.org>
Signed-off-by: Jens Axboe <axboe@kernel.dk>

---

diff --git a/io_uring/net.c b/io_uring/net.c
index fe1c478c7dec..6674a0759390 100644
--- a/io_uring/net.c
+++ b/io_uring/net.c
@@ -788,7 +788,8 @@ int io_recvmsg(struct io_kiocb *req, unsigned int issue_flags)
 	flags = sr->msg_flags;
 	if (force_nonblock)
 		flags |= MSG_DONTWAIT;
-	if (flags & MSG_WAITALL)
+	/* disable partial retry for recvmsg with cmsg attached */
+	if (flags & MSG_WAITALL && !kmsg->controllen)
 		min_ret = iov_iter_count(&kmsg->msg.msg_iter);
 
 	kmsg->msg.msg_get_inq = 1;

-- 
Jens Axboe