[PATCH 7.2 16/82] ALSA: dummy: Check card index validity at probe

[Greg Kroah-Hartman <gregkh@linuxfoundation.org>]

7.2-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Takashi Iwai <tiwai@suse.de>

commit 02442d5fe8ee365a084b055d4fa81a0c1abfc3fd upstream.

snd_dummy_probe() blindly trusts that the given devptr->id value is
within the proper card index range.  It's OK for the devices the
driver itself creates at the module probe time, but if the device is
bound manually via sysfs interface, this could be -1 as "none", and
this leads to OOB access for index[] and other parameters.

Add a sanity check for the card index and warn/correct it if it's a
value out of the range.

Reported-by: syzbot+2fb5d1f7cc4c1f132bcc@syzkaller.appspotmail.com
Closes: https://lore.kernel.org/6a73bd4d.01d0871a.3a0d52.0005.GAE@google.com
Cc: <stable@vger.kernel.org>
Link: https://patch.msgid.link/20260806100433.1287393-1-tiwai@suse.de
Signed-off-by: Takashi Iwai <tiwai@suse.de>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
 sound/drivers/dummy.c |    6 ++++++
 1 file changed, 6 insertions(+)

--- a/sound/drivers/dummy.c
+++ b/sound/drivers/dummy.c
@@ -1017,6 +1017,12 @@ static int snd_dummy_probe(struct platfo
 	int idx, err;
 	int dev = devptr->id;
 
+	if (dev < 0 || dev >= SNDRV_CARDS) {
+		dev_warn(&devptr->dev,
+			 "Invalid card index %d, using default 0\n", dev);
+		dev = 0;
+	}
+
 	err = snd_devm_card_new(&devptr->dev, index[dev], id[dev], THIS_MODULE,
 				sizeof(struct snd_dummy), &card);
 	if (err < 0)