[PATCH] ALSA: 6fire: fix use-after-free on disconnect
From: Berk Cem Goksel
Date: Fri Apr 10 2026 - 01:13:58 EST
In usb6fire_chip_abort(), the chip struct is allocated as the card's
private data (via snd_card_new with sizeof(struct sfire_chip)). When
snd_card_free_when_closed() is called and no file handles are open, the
card and embedded chip are freed synchronously. The subsequent
chip->card = NULL write then hits freed slab memory.
Call trace:
usb6fire_chip_abort sound/usb/6fire/chip.c:59 [inline]
usb6fire_chip_disconnect+0x348/0x358 sound/usb/6fire/chip.c:182
usb_unbind_interface+0x1a8/0x88c drivers/usb/core/driver.c:458
...
hub_event+0x1a04/0x4518 drivers/usb/core/hub.c:5953
Fix by moving the card lifecycle out of usb6fire_chip_abort() and into
usb6fire_chip_disconnect(). The card pointer is saved in a local
before any teardown, snd_card_disconnect() is called first to prevent
new opens, URBs are aborted while chip is still valid, and
snd_card_free_when_closed() is called last so chip is never accessed
after the card may be freed.
Fixes: a0810c3d6dd2 ("ALSA: 6fire: Release resources at card release")
Cc: stable@xxxxxxxxxxxxxxx
Cc: Andrey Konovalov <andreyknvl@xxxxxxxxx>
Signed-off-by: Berk Cem Goksel <berkcgoksel@xxxxxxxxx>
---
Patch applies to 7.0-rc6 (upstream master 5619b098e2fb).
Tested on 7.0.0-rc5 (arm64) with KASAN:
[ 11.274798] BUG: KASAN: slab-use-after-free in usb6fire_chip_abort sound/usb/6fire/chip.c:59 [inline]
[ 11.274798] BUG: KASAN: slab-use-after-free in usb6fire_chip_disconnect+0x348/0x358 sound/usb/6fire/chip.c:182
[ 11.275503] Write of size 8 at addr ffff000013230a98 by task kworker/0:1/12
[ 11.276469] CPU: 0 UID: 0 PID: 12 Comm: kworker/0:1 Not tainted 7.0.0-rc5-g663cf2b1ad64-dirty #10 PREEMPT
[ 11.276485] Hardware name: linux,dummy-virt (DT)
[ 11.276504] Workqueue: usb_hub_wq hub_event
[ 11.276562] Call trace:
[ 11.276582] show_stack+0x2c/0x3c arch/arm64/kernel/stacktrace.c:499 (C)
[ 11.276616] dump_stack_lvl+0x138/0x1c8 lib/dump_stack.c:120
[ 11.276666] print_report+0x118/0x5d4 mm/kasan/report.c:482
[ 11.276669] kasan_report+0xc0/0x100 mm/kasan/report.c:595
[ 11.276678] __asan_report_store8_noabort+0x20/0x2c mm/kasan/report_generic.c:386
[ 11.276684] usb6fire_chip_abort sound/usb/6fire/chip.c:59 [inline]
[ 11.276688] usb6fire_chip_disconnect+0x348/0x358 sound/usb/6fire/chip.c:182
[ 11.276692] usb_unbind_interface+0x1a8/0x88c drivers/usb/core/driver.c:458
[ 11.276697] device_release_driver_internal+0x450/0x63c drivers/base/dd.c:1367
[ 11.276699] bus_remove_device+0x2a0/0x4f4 drivers/base/bus.c:657
[ 11.276701] device_del+0x31c/0x870 drivers/base/core.c:3880
[ 11.276720] usb_disable_device+0x2e8/0x6ec drivers/usb/core/message.c:1476
[ 11.276737] usb_disconnect+0x294/0x8d8 drivers/usb/core/hub.c:2345
[ 11.276776] hub_event+0x1a04/0x4518 drivers/usb/core/hub.c:5953
[ 11.276836] process_one_work+0x8a4/0x1dc0 kernel/workqueue.c:3276
[ 11.276850] worker_thread+0x57c/0xcac kernel/workqueue.c:3440
[ 11.276888] kthread+0x3e4/0x494 kernel/kthread.c:436
[ 11.276890] ret_from_fork+0x10/0x20 arch/arm64/kernel/entry.S:860
[ 11.339324] Allocated by task 12:
[ 11.339765] kasan_save_stack+0x3c/0x64 mm/kasan/common.c:57
[ 11.340193] kasan_save_track+0x20/0x3c mm/kasan/common.c:78
[ 11.340615] __kasan_kmalloc+0xb8/0xbc mm/kasan/common.c:415
[ 11.341108] snd_card_new+0x70/0x11c sound/core/init.c:184
[ 11.341555] usb6fire_chip_probe+0x298/0x864 sound/usb/6fire/chip.c:120
[ 11.353835] Freed by task 12:
[ 11.354171] kasan_save_stack+0x3c/0x64 mm/kasan/common.c:57
[ 11.354599] kasan_save_track+0x20/0x3c mm/kasan/common.c:78
[ 11.355023] kasan_save_free_info+0x4c/0x78 mm/kasan/generic.c:584
[ 11.355505] __kasan_slab_free+0x5c/0x88 mm/kasan/common.c:285
[ 11.355945] kfree+0x164/0x61c mm/slub.c:6483
[ 11.356285] snd_card_do_free sound/core/init.c:597 [inline]
[ 11.356778] release_card_device+0x16c/0x1fc sound/core/init.c:153
[ 11.357221] snd_card_free_when_closed+0x30/0x44 sound/core/init.c:612
[ 11.357696] usb6fire_chip_abort sound/usb/6fire/chip.c:58 [inline]
[ 11.358103] usb6fire_chip_disconnect+0x298/0x358 sound/usb/6fire/chip.c:182
sound/usb/6fire/chip.c | 17 ++++++++++++-----
1 file changed, 12 insertions(+), 5 deletions(-)
diff --git a/sound/usb/6fire/chip.c b/sound/usb/6fire/chip.c
index 5ff78814e687..874f6cd503ca 100644
--- a/sound/usb/6fire/chip.c
+++ b/sound/usb/6fire/chip.c
@@ -53,11 +53,6 @@ static void usb6fire_chip_abort(struct sfire_chip *chip)
usb6fire_comm_abort(chip);
if (chip->control)
usb6fire_control_abort(chip);
- if (chip->card) {
- snd_card_disconnect(chip->card);
- snd_card_free_when_closed(chip->card);
- chip->card = NULL;
- }
}
}
@@ -168,6 +163,7 @@ static int usb6fire_chip_probe(struct usb_interface *intf,
static void usb6fire_chip_disconnect(struct usb_interface *intf)
{
struct sfire_chip *chip;
+ struct snd_card *card;
chip = usb_get_intfdata(intf);
if (chip) { /* if !chip, fw upload has been performed */
@@ -178,8 +174,19 @@ static void usb6fire_chip_disconnect(struct usb_interface *intf)
chips[chip->regidx] = NULL;
}
+ /*
+ * Save card pointer before teardown.
+ * snd_card_free_when_closed() may free card (and
+ * the embedded chip) immediately, so it must be
+ * called last and chip must not be accessed after.
+ */
+ card = chip->card;
chip->shutdown = true;
+ if (card)
+ snd_card_disconnect(card);
usb6fire_chip_abort(chip);
+ if (card)
+ snd_card_free_when_closed(card);
}
}
}
--
2.34.1