virtio-snd: fix max_size bounds check in input cb

In 98e77e3d we calculated the max size and checked that each buffer is smaller than it.

We neglected to subtract the size of the virtio_snd_pcm_status header
from the max size, and max_size was thus larger than the correct value,
leading to potential OOB writes.

If the buffer cannot fit the header or can fit only the header, return
the buffer immediately.

Cc: qemu-stable@nongnu.org
Fixes: 98e77e3dd8dd6e7aa9a7dffa60f49c8c8a49d4e3 ("virtio-snd: add max size bounds check in input cb")
Reported-by: DARKNAVY <vr@darknavy.com>
Signed-off-by: Manos Pitsidianakis <manos.pitsidianakis@linaro.org>
Reviewed-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
Message-Id: <20260220-virtio-snd-series-v1-4-207c4f7200a2@linaro.org>
(cherry picked from commit bcb53328aa70023f1405fade4e253e7f77567261)
Signed-off-by: Michael Tokarev <mjt@tls.msk.ru>

1 files changed, 6 insertions, 0 deletions

diff --git a/hw/audio/virtio-snd.c b/hw/audio/virtio-snd.c
index 38d9a9712c..effae20bf0 100644
--- a/hw/audio/virtio-snd.c
+++ b/hw/audio/virtio-snd.c
@@ -1255,6 +1255,12 @@ static void virtio_snd_pcm_in_cb(void *data, int available)
             }
 
             max_size = iov_size(buffer->elem->in_sg, buffer->elem->in_num);
+            if (max_size <= sizeof(virtio_snd_pcm_status)) {
+                return_rx_buffer(stream, buffer);
+                continue;
+            }
+            max_size -= sizeof(virtio_snd_pcm_status);
+
             for (;;) {
                 if (buffer->size >= max_size) {
                     return_rx_buffer(stream, buffer);