FAILED: patch "[PATCH] ALSA: usb-audio: Fix potential overflow of PCM transfer" failed to apply to 5.4-stable tree

The patch below does not apply to the 5.4-stable tree.
If someone wants it applied there, or to any other stable or longterm tree, then please email the backport, including the original git commit id to <[email protected]>.

To reproduce the conflict and resubmit, you may use the following commands:

git fetch https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/ linux-5.4.y
git checkout FETCH_HEAD
git cherry-pick -x 05a1fc5efdd8560f34a3af39c9cf1e1526cc3ddf
# <resolve conflicts, build, test, etc.>
git commit -s
git send-email --to '<[email protected]>' --in-reply-to '2025112037-brick-dreadful-388a@gregkh' --subject-prefix 'PATCH 5.4.y' HEAD^..

Possible dependencies:

thanks,

greg k-h

------------------ original commit in Linus's tree ------------------

From 05a1fc5efdd8560f34a3af39c9cf1e1526cc3ddf Mon Sep 17 00:00:00 2001
From: Takashi Iwai <[email protected]>
Date: Sun, 9 Nov 2025 10:12:07 +0100
Subject: [PATCH] ALSA: usb-audio: Fix potential overflow of PCM transfer
buffer

The PCM stream data in USB-audio driver is transferred over USB URB packet buffers, and each packet size is determined dynamically. The packet sizes are limited by some factors such as wMaxPacketSize USB descriptor. OTOH, in the current code, the actually used packet sizes are determined only by the rate and the PPS, which may be bigger than the size limit above. This results in a buffer overflow, as reported by syzbot.

Basically when the limit is smaller than the calculated packet size, it implies that something is wrong, most likely a weird USB descriptor. So the best option would be just to return an error at the parameter setup time before doing any further operations.

This patch introduces such a sanity check, and returns -EINVAL when the packet size is greater than maxpacksize. The comparison with ep->packsize[1] alone should suffice since it's always equal or greater than ep->packsize[0].

index 880f5afcce60..cc15624ecaff 100644
@@ -1362,6 +1362,11 @@ int snd_usb_endpoint_set_params(struct snd_usb_audio *chip,
 	ep->sample_rem = ep->cur_rate % ep->pps;
 	ep->packsize[0] = ep->cur_rate / ep->pps;
 	ep->packsize[1] = (ep->cur_rate + (ep->pps - 1)) / ep->pps;
+	if (ep->packsize[1] > ep->maxpacksize) {
+		usb_audio_dbg(chip, "Too small maxpacksize %u for rate %u / pps %u\n",
+			      ep->maxpacksize, ep->cur_rate, ep->pps);
+		return -EINVAL;
+	}
 
 	/* calculate the frequency in 16.16 format */
 	ep->freqm = ep->freqn;