ALSA: usb-audio: Clamp frame size in implicit-feedback mode

snd_usb_handle_sync_urb() scales received sync packet sizes by the sender's
stride and stores the result directly in out_packet->packet_size[i]. If a
connected USB device sends an oversized sync packet, this frame count can
exceed ep->maxframesize.

The un-clamped frame count then propagates to the playback endpoint queue,
potentially driving packet transfers beyond the endpoint's hardware frame
limits.

Cap the calculated frame count against ep->maxframesize in
snd_usb_handle_sync_urb() to prevent oversized packets from entering the
playback queue.

Fixes: 28acb12014fb ("ALSA: usb-audio: use sender stride for implicit feedback")
Cc: stable@vger.kernel.org
Assisted-by: Jetski:Gemini-3.6-Flash
Signed-off-by: Sonali Pradhan <sonalipradhan@google.com>
Link: https://patch.msgid.link/20260728202432.2354994-1-sonalipradhan@google.com
Signed-off-by: Takashi Iwai <tiwai@suse.de>

diff --git a/sound/usb/endpoint.c b/sound/usb/endpoint.c
index 91611d0a4e48571da5277975963bf061b5319343..dca06ba1c67e0b7f8d652ff6d6df6c13d71cb129 100644 (file)
--- a/sound/usb/endpoint.c
+++ b/sound/usb/endpoint.c
@@ -1819,11 +1819,13 @@ static void snd_usb_handle_sync_urb(struct snd_usb_endpoint *ep,
 
                out_packet->packets = in_ctx->packets;
                for (i = 0; i < in_ctx->packets; i++) {
-                       if (urb->iso_frame_desc[i].status == 0)
-                               out_packet->packet_size[i] =
+                       if (urb->iso_frame_desc[i].status == 0) {
+                               unsigned int frames =
                                        urb->iso_frame_desc[i].actual_length / sender->stride;
-                       else
+                               out_packet->packet_size[i] = min(frames, ep->maxframesize);
+                       } else {
                                out_packet->packet_size[i] = 0;
+                       }
                }
 
                spin_unlock_irqrestore(&ep->lock, flags);