[PATCH v2] 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.

Move the MSG_WAITALL check into the non-multishot case while at it,
since MSG_WAITALL is explicitly disabled for multishot anyway.

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>
---

v2: correct msg_controllen check and move into non-mshot branch

 io_uring/net.c | 11 +++++++----
 1 file changed, 7 insertions(+), 4 deletions(-)

diff --git a/io_uring/net.c b/io_uring/net.c
index c0924ab1ea11..2bc2cb2f4d6c 100644
--- a/io_uring/net.c
+++ b/io_uring/net.c
@@ -789,16 +789,19 @@ 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)
-		min_ret = iov_iter_count(&kmsg->msg.msg_iter);
 
 	kmsg->msg.msg_get_inq = 1;
-	if (req->flags & REQ_F_APOLL_MULTISHOT)
+	if (req->flags & REQ_F_APOLL_MULTISHOT) {
 		ret = io_recvmsg_multishot(sock, sr, kmsg, flags,
 					   &mshot_finished);
-	else
+	} else {
+		/* disable partial retry for recvmsg with cmsg attached */
+		if (flags & MSG_WAITALL && !kmsg->msg.msg_controllen)
+			min_ret = iov_iter_count(&kmsg->msg.msg_iter);
+
 		ret = __sys_recvmsg_sock(sock, &kmsg->msg, sr->umsg,
 					 kmsg->uaddr, flags);
+	}
 
 	if (ret < min_ret) {
 		if (ret == -EAGAIN && force_nonblock) {
-- 
2.39.2

-- 
Jens Axboe