FAILED: patch "[PATCH] ALSA: usb-audio: Clamp implicit feedback packet count to URB" failed to apply to 6.18-stable tree

The patch below does not apply to the 6.18-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-6.18.y
git checkout FETCH_HEAD
git cherry-pick -x 76a986c980bb502c7688d605ac7a67fd257a9a1b
# <resolve conflicts, build, test, etc.>
git commit -s
git send-email --to '<[email protected]>' --in-reply-to '2026092245-renewably-elevate-ca0d@gregkh' --subject-prefix 'PATCH 6.18.y' 'HEAD^..'

Possible dependencies:

thanks,

greg k-h

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

From 76a986c980bb502c7688d605ac7a67fd257a9a1b Mon Sep 17 00:00:00 2001
From: Xiang Mei <[email protected]>
Date: Sat, 12 Sep 2026 13:05:30 -0700
Subject: [PATCH] ALSA: usb-audio: Clamp implicit feedback packet count to URB
capacity

data_ep_set_params() allocates each data URB for exactly u->packets isochronous frames, so urb->iso_frame_desc[] has u->packets slots and ctx->packets is the driver's only record of that limit. For an implicit feedback sink, snd_usb_queue_pending_output_urbs() overwrites it with the sync source's packet count, which is calculated independently from the capture endpoint's parameters. When that count is larger, prepare_playback_urb() and prepare_silent_urb() can write iso_frame_desc[] past the allocation; their existing bounds limit payload bytes, not the descriptor index.

The reproducer uses a high-speed UAC2 device declaring bInterval 1 for implicit feedback capture (8 packets) and bInterval 4 for playback (1 packet). On the first capture completion after the stream starts, it accesses seven descriptors spanning 112 bytes beyond the one-packet URB:

  BUG: KASAN: slab-out-of-bounds in prepare_playback_urb (sound/usb/pcm.c:1560)
  Write of size 4 at addr ffff88801e696ad0 by task vhci_rx/178
   prepare_playback_urb (sound/usb/pcm.c:1560)
   prepare_outbound_urb (sound/usb/endpoint.c:340)
   snd_usb_queue_pending_output_urbs (sound/usb/endpoint.c:501)
   snd_complete_urb (sound/usb/endpoint.c:1834)
   __usb_hcd_giveback_urb (drivers/usb/core/hcd.c:1657)
   usb_hcd_giveback_urb (drivers/usb/core/hcd.c:1741)
   vhci_rx_loop (drivers/usb/usbip/vhci_rx.c:107)
   kthread (kernel/kthread.c:436)
  The buggy address belongs to the object at ffff88801e696a00
   which belongs to the cache kmalloc-256 of size 256
  The buggy address is located 0 bytes to the right of
   allocated 208-byte region [ffff88801e696a00, ffff88801e696ad0)

Record the allocated packet count per endpoint and clamp both the adopted count and the packet-size copy to it. Fold the Format Type II delimiter into urb_packs before the allocation loop so the recorded limit matches every URB.

index e34d92d576a2..8299ac241c60 100644
@@ -116,6 +116,7 @@ struct snd_usb_endpoint {
 	unsigned int phase;		/* phase accumulator */
 	unsigned int maxpacksize;	/* max packet size in bytes */
 	unsigned int maxframesize;      /* max packet size in frames */
+	unsigned int max_urb_packs;	/* packets allocated per data URB */
 	unsigned int max_urb_frames;	/* max URB size in frames */
 	unsigned int curpacksize;	/* current packet size in bytes (for capture) */
 	unsigned int curframesize;      /* current packet size in frames (for capture) */

index 0835943d7b0e..b72ce1e9bfb1 100644
@@ -492,9 +492,10 @@ int snd_usb_queue_pending_output_urbs(struct snd_usb_endpoint *ep,
 
 		/* copy over the length information */
 		if (implicit_fb) {
-			ctx->packets = packet->packets;
+			ctx->packets = min_t(int, packet->packets,
+					     ep->max_urb_packs);
 			memcpy(ctx->packet_size, packet->packet_size,
-			       packet->packets * sizeof(packet->packet_size[0]));
+			       ctx->packets * sizeof(packet->packet_size[0]));
 		}
 
 		/* call the data handler to fill in playback data */

@@ -1242,15 +1243,16 @@ static int data_ep_set_params(struct snd_usb_endpoint *ep)
 			ep->nurbs = min(max_urbs, urbs_per_period * ep->cur_buffer_periods);
 	}
 
+	if (fmt->fmt_type == UAC_FORMAT_TYPE_II)
+		urb_packs++; /* for transfer delimiter */
+	ep->max_urb_packs = urb_packs;
+
 	/* allocate and initialize data urbs */
 	for (i = 0; i < ep->nurbs; i++) {
 		struct snd_urb_ctx *u = &ep->urb[i];
 		u->index = i;
 		u->ep = ep;
 		u->packets = urb_packs;
-
-		if (fmt->fmt_type == UAC_FORMAT_TYPE_II)
-			u->packets++; /* for transfer delimiter */
 		u->buffer_size = maxsize * u->packets;
 		u->urb = usb_alloc_urb(u->packets, GFP_KERNEL);
 		if (!u->urb)

From: Takashi Iwai <[email protected]>

[ Upstream commit 36adb51ac0b19edb32ffeea3fe66b174bad25ead ]

We did manual copies over loop for the packet data update of the implicit feedback, but this can be optimized with a simple memcpy().

Along with it, change the data type of snd_usb_packet_info struct to align with other (from uint32_t to int).

No functional changes but only code optimizations.

Stable-dep-of: 76a986c980bb ("ALSA: usb-audio: Clamp implicit feedback packet count to URB capacity")

---
 sound/usb/card.h     | 2 +-
 sound/usb/endpoint.c | 6 +++---
 2 files changed, 4 insertions(+), 4 deletions(-)

index 94404c24d240d..e34d92d576a27 100644
@@ -90,7 +90,7 @@ struct snd_usb_endpoint {
 	struct snd_urb_ctx urb[MAX_URBS];
 
 	struct snd_usb_packet_info {
-		uint32_t packet_size[MAX_PACKS_HS];
+		int packet_size[MAX_PACKS_HS];
 		int packets;
 	} next_packet[MAX_URBS];
 	unsigned int next_packet_head;	/* ring buffer offset to read */

index bdf0e724d4187..3f46b82561966 100644
@@ -470,7 +470,7 @@ int snd_usb_queue_pending_output_urbs(struct snd_usb_endpoint *ep,
 	while (ep_state_running(ep)) {
 		struct snd_usb_packet_info *packet;
 		struct snd_urb_ctx *ctx = NULL;
-		int err, i;
+		int err;
 
 		scoped_guard(spinlock_irqsave, &ep->lock) {
 			if ((!implicit_fb || ep->next_packet_queued > 0) &&

@@ -490,8 +490,8 @@ int snd_usb_queue_pending_output_urbs(struct snd_usb_endpoint *ep,
 		/* copy over the length information */
 		if (implicit_fb) {
 			ctx->packets = packet->packets;
-			for (i = 0; i < packet->packets; i++)
-				ctx->packet_size[i] = packet->packet_size[i];
+			memcpy(ctx->packet_size, packet->packet_size,
+			       packet->packets * sizeof(packet->packet_size[0]));
 		}
 
 		/* call the data handler to fill in playback data */

2.53.0

From: Xiang Mei <[email protected]>

[ Upstream commit 76a986c980bb502c7688d605ac7a67fd257a9a1b ]

data_ep_set_params() allocates each data URB for exactly u->packets isochronous frames, so urb->iso_frame_desc[] has u->packets slots and ctx->packets is the driver's only record of that limit. For an implicit feedback sink, snd_usb_queue_pending_output_urbs() overwrites it with the sync source's packet count, which is calculated independently from the capture endpoint's parameters. When that count is larger, prepare_playback_urb() and prepare_silent_urb() can write iso_frame_desc[] past the allocation; their existing bounds limit payload bytes, not the descriptor index.

The reproducer uses a high-speed UAC2 device declaring bInterval 1 for implicit feedback capture (8 packets) and bInterval 4 for playback (1 packet). On the first capture completion after the stream starts, it accesses seven descriptors spanning 112 bytes beyond the one-packet URB:

  BUG: KASAN: slab-out-of-bounds in prepare_playback_urb (sound/usb/pcm.c:1560)
  Write of size 4 at addr ffff88801e696ad0 by task vhci_rx/178
   prepare_playback_urb (sound/usb/pcm.c:1560)
   prepare_outbound_urb (sound/usb/endpoint.c:340)
   snd_usb_queue_pending_output_urbs (sound/usb/endpoint.c:501)
   snd_complete_urb (sound/usb/endpoint.c:1834)
   __usb_hcd_giveback_urb (drivers/usb/core/hcd.c:1657)
   usb_hcd_giveback_urb (drivers/usb/core/hcd.c:1741)
   vhci_rx_loop (drivers/usb/usbip/vhci_rx.c:107)
   kthread (kernel/kthread.c:436)
  The buggy address belongs to the object at ffff88801e696a00
   which belongs to the cache kmalloc-256 of size 256
  The buggy address is located 0 bytes to the right of
   allocated 208-byte region [ffff88801e696a00, ffff88801e696ad0)

Record the allocated packet count per endpoint and clamp both the adopted count and the packet-size copy to it. Fold the Format Type II delimiter into urb_packs before the allocation loop so the recorded limit matches every URB.

---
 sound/usb/card.h     |  1 +
 sound/usb/endpoint.c | 12 +++++++-----
 2 files changed, 8 insertions(+), 5 deletions(-)

index e34d92d576a27..8299ac241c603 100644
@@ -116,6 +116,7 @@ struct snd_usb_endpoint {
 	unsigned int phase;		/* phase accumulator */
 	unsigned int maxpacksize;	/* max packet size in bytes */
 	unsigned int maxframesize;      /* max packet size in frames */
+	unsigned int max_urb_packs;	/* packets allocated per data URB */
 	unsigned int max_urb_frames;	/* max URB size in frames */
 	unsigned int curpacksize;	/* current packet size in bytes (for capture) */
 	unsigned int curframesize;      /* current packet size in frames (for capture) */

index 3f46b82561966..b0202ae44b967 100644
@@ -489,9 +489,10 @@ int snd_usb_queue_pending_output_urbs(struct snd_usb_endpoint *ep,
 
 		/* copy over the length information */
 		if (implicit_fb) {
-			ctx->packets = packet->packets;
+			ctx->packets = min_t(int, packet->packets,
+					     ep->max_urb_packs);
 			memcpy(ctx->packet_size, packet->packet_size,
-			       packet->packets * sizeof(packet->packet_size[0]));
+			       ctx->packets * sizeof(packet->packet_size[0]));
 		}
 
 		/* call the data handler to fill in playback data */

@@ -1235,15 +1236,16 @@ static int data_ep_set_params(struct snd_usb_endpoint *ep)
 		ep->nurbs = min(max_urbs, urbs_per_period * ep->cur_buffer_periods);
 	}
 
+	if (fmt->fmt_type == UAC_FORMAT_TYPE_II)
+		urb_packs++; /* for transfer delimiter */
+	ep->max_urb_packs = urb_packs;
+
 	/* allocate and initialize data urbs */
 	for (i = 0; i < ep->nurbs; i++) {
 		struct snd_urb_ctx *u = &ep->urb[i];
 		u->index = i;
 		u->ep = ep;
 		u->packets = urb_packs;
-
-		if (fmt->fmt_type == UAC_FORMAT_TYPE_II)
-			u->packets++; /* for transfer delimiter */
 		u->buffer_size = maxsize * u->packets;
 		u->urb = usb_alloc_urb(u->packets, GFP_KERNEL);
 		if (!u->urb)

2.53.0