virtio-snd: Enhance error handling for invalid transfers

This patch improves error handling in virtio_snd_handle_tx_xfer()
and virtio_snd_handle_rx_xfer() in the VirtIO sound driver. Previously,
'goto' statements were used for error paths, leading to unnecessary
processing and potential null pointer dereferences. Now, 'continue' is
used to skip the rest of the current loop iteration for errors such as
message size discrepancies or null streams, reducing crash risks.

ASAN log illustrating the issue addressed:

ERROR: AddressSanitizer: SEGV on unknown address 0x0000000000b4
    #0 0x57cea39967b8 in qemu_mutex_lock_impl qemu/util/qemu-thread-posix.c:92:5
    #1 0x57cea128c462 in qemu_mutex_lock qemu/include/qemu/thread.h:122:5
    #2 0x57cea128d72f in qemu_lockable_lock qemu/include/qemu/lockable.h:95:5
    #3 0x57cea128c294 in qemu_lockable_auto_lock qemu/include/qemu/lockable.h:105:5
    #4 0x57cea1285eb2 in virtio_snd_handle_rx_xfer qemu/hw/audio/virtio-snd.c:1026:9
    qemu#5 0x57cea2caebbc in virtio_queue_notify_vq qemu/hw/virtio/virtio.c:2268:9
    qemu#6 0x57cea2cae412 in virtio_queue_host_notifier_read qemu/hw/virtio/virtio.c:3671:9
    qemu#7 0x57cea39822f1 in aio_dispatch_handler qemu/util/aio-posix.c:372:9
    qemu#8 0x57cea3979385 in aio_dispatch_handlers qemu/util/aio-posix.c:414:20
    qemu#9 0x57cea3978eb1 in aio_dispatch qemu/util/aio-posix.c:424:5
    qemu#10 0x57cea3a1eede in aio_ctx_dispatch qemu/util/async.c:360:5

Signed-off-by: Zheyu Ma <zheyuma97@gmail.com>
Reviewed-by: Manos Pitsidianakis <manos.pitsidianakis@linaro.org>
Message-Id: <20240322110827.568412-1-zheyuma97@gmail.com>
Reviewed-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>

hw/audio/virtio-snd.c

@@ -913,13 +913,13 @@ static void virtio_snd_handle_tx_xfer(VirtIODevice *vdev, VirtQueue *vq)
                             &hdr,
                             sizeof(virtio_snd_pcm_xfer));
         if (msg_sz != sizeof(virtio_snd_pcm_xfer)) {
-            goto tx_err;
+            continue;
         }
         stream_id = le32_to_cpu(hdr.stream_id);
 
         if (stream_id >= s->snd_conf.streams
             || s->pcm->streams[stream_id] == NULL) {
-            goto tx_err;
+            continue;
         }
 
         stream = s->pcm->streams[stream_id];
@@ -995,13 +995,13 @@ static void virtio_snd_handle_rx_xfer(VirtIODevice *vdev, VirtQueue *vq)
                             &hdr,
                             sizeof(virtio_snd_pcm_xfer));
         if (msg_sz != sizeof(virtio_snd_pcm_xfer)) {
-            goto rx_err;
+            continue;
         }
         stream_id = le32_to_cpu(hdr.stream_id);
 
         if (stream_id >= s->snd_conf.streams
             || !s->pcm->streams[stream_id]) {
-            goto rx_err;
+            continue;
         }
 
         stream = s->pcm->streams[stream_id];