[PATCH 4.9 29/50] ALSA: ac97: Fix incorrect bit shift at AC97-SPSA control write

Greg Kroah-Hartman
2018-12-04T11:08:35Z

From: Takashi Iwai <tiwai@suse.de>

commit 7194eda1ba0872d917faf3b322540b4f57f11ba5 upstream.

The function snd_ac97_put_spsa() gets the bit shift value from the
associated private_value, but it extracts too much; the current code
extracts 8 bit values in bits 8-15, but this is a combination of two
nibbles (bits 8-11 and bits 12-15) for left and right shifts.
Due to the incorrect bits extraction, the actual shift may go beyond
the 32bit value, as spotted recently by UBSAN check:
UBSAN: Undefined behaviour in sound/pci/ac97/ac97_codec.c:836:7
shift exponent 68 is too large for 32-bit type 'int'

This patch fixes the shift value extraction by masking the properly
with 0x0f instead of 0xff.

Reported-and-tested-by: Meelis Roos <mroos@linux.ee>
Cc: <stable@vger.kernel.org>
Signed-off-by: Takashi Iwai <tiwai@suse.de>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
sound/pci/ac97/ac97_codec.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)

--- a/sound/pci/ac97/ac97_codec.c
+++ b/sound/pci/ac97/ac97_codec.c
@@ -824,7 +824,7 @@ static int snd_ac97_put_spsa(struct snd_
{
struct snd_ac97 *ac97 = snd_kcontrol_chip(kcontrol);
int reg = kcontrol->private_value & 0xff;
- int shift = (kcontrol->private_value >> 8) & 0xff;
+ int shift = (kcontrol->private_value >> 8) & 0x0f;
int mask = (kcontrol->private_value >> 16) & 0xff;
// int invert = (kcontrol->private_value >> 24) & 0xff;
unsigned short value, old, new;