[alsa-devel] [patch] ALSA: bits vs bytes bug in snd_card_create()

[walter harms]

Am 23.01.2014 09:21, schrieb Dan Carpenter:
> The test here is intended intended to prevent shift wrapping bugs when
> we do "1U << idx2".  We should consider the number of bits in a u32
> instead of the number of bytes.
> 
> Fixes: 7bb2491b35a2 ('ALSA: Add kconfig to specify the max card numbers')
> Signed-off-by: Dan Carpenter <dan.carpenter at oracle.com>
> ---
> WARNING:  Please check this one carefully because I might be wrong.
> 
> diff --git a/sound/core/init.c b/sound/core/init.c
> index 1351f22f651c..e9e3db321e64 100644
> --- a/sound/core/init.c
> +++ b/sound/core/init.c
> @@ -183,7 +183,7 @@ int snd_card_create(int idx, const char *xid,
>  	if (idx < 0) {
>  		for (idx2 = 0; idx2 < SNDRV_CARDS; idx2++) {
>  			/* idx == -1 == 0xffff means: take any free slot */
> -			if (idx2 < sizeof(int) && !(idx & (1U << idx2)))
> +			if (idx2 < 32 && !(idx & (1U << idx2)))
>  				continue;
>  			if (!test_bit(idx2, snd_cards_lock)) {
>  				if (!slots[idx2] || !*slots[idx2]) {
> --

Funny bug,
to be 100% sure you could multiply by CHAR_BIT ;)

other code simple does (1UL << (nr & 31))
on the other side a check like:

#if SNDRV_CARDS > 32
# error to much sound
#endif

whould give the user a hint what is going on instead of silently ignoring
that error.

re,
 wh


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