[PATCH 6.18 189/198] ALSA: 6fire: fix use-after-free on disconnect

Greg Kroah-Hartman
2026-04-20T16:05:18Z

From: Berk Cem Goksel <berkcgoksel@gmail.com>

commit b9c826916fdce6419b94eb0cd8810fdac18c2386 upstream.

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@vger.kernel.org
Cc: Andrey Konovalov <andreyknvl@gmail.com>
Signed-off-by: Berk Cem Goksel <berkcgoksel@gmail.com>
Link: https://patch.msgid.link/20260410051341.1069716-1-berkcgoksel@gmail.com
Signed-off-by: Takashi Iwai <tiwai@suse.de>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
sound/usb/6fire/chip.c | 17 ++++++++++++-----
1 file changed, 12 insertions(+), 5 deletions(-)

--- a/sound/usb/6fire/chip.c
+++ b/sound/usb/6fire/chip.c
@@ -53,11 +53,6 @@ static void usb6fire_chip_abort(struct s
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 @@ destroy_chip:
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(str
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);
}
}
}