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 8ead497..41f828d 100644 (file)
--- a/io_uring/net.c
+++ b/io_uring/net.c
@@ -781,16 +781,19 @@ 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) {