CVE-2026-31778

In the Linux kernel, the following vulnerability has been resolved:

ALSA: caiaq: fix stack out-of-bounds read in init_card

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.