Re: [PATCH] ALSA: caiaq: fix stack out-of-bounds read in init_card

[Takashi Iwai <tiwai@suse.de>]

On Sun, 29 Mar 2026 15:38:25 +0200,
Berk Cem Goksel wrote:
> 
> The loop creates a whitespace-stripped copy of the card shortname
> where `len < sizeof(card->id)` is used for the bounds check. Since
> sizeof(card->id) is 16 and the local id buffer is also 16 bytes,
> writing 16 non-space characters fills the entire buffer,
> overwriting the terminating nullbyte.
> 
> When this non-null-terminated string is later passed to
> snd_card_set_id() -> copy_valid_id_string(), the function scans
> forward with `while (*nid && ...)` and reads past the end of the
> stack buffer, reading the contents of the stack.
> 
> A USB device with a product name containing many non-ASCII, non-space
> characters (e.g. multibyte UTF-8) will reliably trigger this as follows:
> 
>   BUG: KASAN: stack-out-of-bounds in copy_valid_id_string
>        sound/core/init.c:696 [inline]
>   BUG: KASAN: stack-out-of-bounds in snd_card_set_id_no_lock+0x698/0x74c
>        sound/core/init.c:718
> 
> The off-by-one has been present since commit bafeee5b1f8d ("ALSA:
> snd_usb_caiaq: give better shortname") from June 2009 (v2.6.31-rc1),
> which first introduced this whitespace-stripping loop. The original
> code never accounted for the null terminator when bounding the copy.
> 
> Fix this by changing the loop bound to `sizeof(card->id) - 1`,
> ensuring at least one byte remains as the null terminator.
> 
> Fixes: bafeee5b1f8d ("ALSA: snd_usb_caiaq: give better shortname")
> Cc: stable@vger.kernel.org
> Cc: Andrey Konovalov <andreyknvl@gmail.com>
> Reported-by: Berk Cem Goksel <berkcgoksel@gmail.com>
> Signed-off-by: Berk Cem Goksel <berkcgoksel@gmail.com>

Applied now.  Thanks.


Takashi