hv_sock: Return -EIO for malformed/short packets

Commit f63152958994 fixes a regression, however it fails to report an
error for malformed/short packets -- normally we should never see such
packets, but let's report an error for them just in case.

Fixes: f63152958994 ("hv_sock: Report EOF instead of -EIO for FIN")
Cc: stable@vger.kernel.org
Signed-off-by: Dexuan Cui <decui@microsoft.com>

As of today (4/21/2026), the patch is pending in review:
https://lwn.net/ml/linux-kernel/20260421174931.1152238-1-decui%40microsoft.com/

Author: dcui

net/vmw_vsock/hyperv_transport.c

@@ -704,18 +704,27 @@ static s64 hvs_stream_has_data(struct vsock_sock *vsk)
 		if (hvs->recv_desc) {
 			/* Here hvs->recv_data_len is 0, so hvs->recv_desc must
 			 * be NULL unless it points to the 0-byte-payload FIN
-			 * packet: see hvs_update_recv_data().
+			 * packet or a malformed/short packet: see
+			 * hvs_update_recv_data().
 			 *
-			 * Here all the payload has been dequeued, but
-			 * hvs_channel_readable_payload() still returns 1,
-			 * because the VMBus ringbuffer's read_index is not
-			 * updated for the FIN packet: hvs_stream_dequeue() ->
-			 * hv_pkt_iter_next() updates the cached priv_read_index
-			 * but has no opportunity to update the read_index in
-			 * hv_pkt_iter_close() as hvs_stream_has_data() returns
-			 * 0 for the FIN packet, so it won't get dequeued.
+			 * If hvs->recv_desc points to the FIN packet, here all
+			 * the payload has been dequeued and the peer_shutdown
+			 * flag is set, but hvs_channel_readable_payload() still
+			 * returns 1, because the VMBus ringbuffer's read_index
+			 * is not updated for the FIN packet:
+			 * hvs_stream_dequeue() -> hv_pkt_iter_next() updates
+			 * the cached priv_read_index but has no opportunity to
+			 * update the read_index in hv_pkt_iter_close() as
+			 * hvs_stream_has_data() returns 0 for the FIN packet,
+			 * so it won't get dequeued.
+			 *
+			 * In case hvs->recv_desc points to a malformed/short
+			 * packet, return -EIO.
 			 */
-			return 0;
+			if (hvs->vsk->peer_shutdown & SEND_SHUTDOWN)
+				return 0;
+			else
+				return -EIO;
 		}
 
 		hvs->recv_desc = hv_pkt_iter_first(hvs->chan);