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SubjectRe: [PATCH] pcm_native: Remove VLA usage
On Wed, Mar 28, 2018 at 3:11 PM, Kyle Spiers <kyle@spiers.me> wrote:
> As part of the effort to remove VLAs from the kernel[1], this changes
> the allocation of the rstamps array from being on the stack to being
> kcalloc()ed. This also allows for the removal of the explicit zeroing
> loop.
>
> [1] https://lkml.org/lkml/2018/3/7/621
>
> Signed-off-by: Kyle Spiers <kyle@spiers.me>
> ---
> sound/core/pcm_native.c | 8 +++++---
> 1 file changed, 5 insertions(+), 3 deletions(-)
>
> diff --git a/sound/core/pcm_native.c b/sound/core/pcm_native.c
> index 77ba50d..57240b8 100644
> --- a/sound/core/pcm_native.c
> +++ b/sound/core/pcm_native.c
> @@ -323,7 +323,7 @@ static int constrain_params_by_rules(struct snd_pcm_substream *substream,
> struct snd_pcm_hw_constraints *constrs =
> &substream->runtime->hw_constraints;
> unsigned int k;
> - unsigned int rstamps[constrs->rules_num];
> + unsigned int *rstamps;
> unsigned int vstamps[SNDRV_PCM_HW_PARAM_LAST_INTERVAL + 1];
> unsigned int stamp;
> struct snd_pcm_hw_rule *r;
> @@ -339,8 +339,8 @@ static int constrain_params_by_rules(struct snd_pcm_substream *substream,
> * Each member of 'rstamps' array represents the sequence number of
> * recent application of corresponding rule.
> */
> - for (k = 0; k < constrs->rules_num; k++)
> - rstamps[k] = 0;
> +
> + rstamps = kcalloc(constrs->rules_num, sizeof(*rstamps), GFP_KERNEL);
>
> /*
> * Each member of 'vstamps' array represents the sequence number of
> @@ -399,6 +399,7 @@ static int constrain_params_by_rules(struct snd_pcm_substream *substream,
>
> changed = r->func(params, r);
> if (changed < 0)
> + kfree(rstamps);
> return changed;

Whoops, this needs { } s:

if (changed < 0) {
kfree(rstamps);
return changed;
}

Otherwise, looks good! Once that's fixed:

Reviewed-by: Kees Cook <keescook@chromium.org>

-Kees

>
> /*
> @@ -430,6 +431,7 @@ static int constrain_params_by_rules(struct snd_pcm_substream *substream,
> if (again)
> goto retry;
>
> + kfree(rstamps);
> return 0;
> }
>
> --
> 2.7.4
>



--
Kees Cook
Pixel Security

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