io_uring/net: disable partial retries for recvmsg with cmsg

commit 78d0d2063bab954d19a1696feae4c7706a626d48 upstream.

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>
Reviewed-by: Stefan Metzmacher <metze@samba.org>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/io_uring/net.c b/io_uring/net.c
index 110c2c95aa47b962262a387dda6f58c0d1de87b9..49dc43d1d9fd57c0c346dd45773ae0617c5d6b8e 100644 (file)
--- a/io_uring/net.c
+++ b/io_uring/net.c
@@ -789,16 +789,19 @@ retry_multishot:
        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) {