Re: [FFmpeg-devel] [PATCH] checkasm/h264dsp: Fix stack overflow in check_idct_dequant

[Andreas Rheinhardt <andreas.rheinhardt@outlook.com>]

Zhao Zhili:
> From: Zhao Zhili <zhilizhao@tencent.com>
> 
> ---
>  tests/checkasm/h264dsp.c | 14 ++++++++++----
>  1 file changed, 10 insertions(+), 4 deletions(-)
> 
> diff --git a/tests/checkasm/h264dsp.c b/tests/checkasm/h264dsp.c
> index f5f9650224..006532e08b 100644
> --- a/tests/checkasm/h264dsp.c
> +++ b/tests/checkasm/h264dsp.c
> @@ -328,7 +328,7 @@ static void check_idct_multiple(void)
>  static void check_idct_dequant(void)
>  {
>      static const int depths[5] = { 8, 9, 10, 12, 14 };
> -    LOCAL_ALIGNED_16(int16_t, src, [16]);
> +    LOCAL_ALIGNED_16(int16_t, src, [16 * 2]);
>      /* Ensure dst buffers are large enough to hold dctcoefs of all bit-depths. */
>      LOCAL_ALIGNED_16(uint8_t, dst0, [16 * 16 * sizeof(int32_t)]);
>      LOCAL_ALIGNED_16(uint8_t, dst1, [16 * 16 * sizeof(int32_t)]);
> @@ -338,15 +338,21 @@ static void check_idct_dequant(void)
>      int bit_depth, i, qmul;
>      declare_func_emms(AV_CPU_FLAG_MMX | AV_CPU_FLAG_SSE2, void, int16_t *output, int16_t *input, int qmul);
>  
> -    for (int j = 0; j < 16; j++)
> -        src[j] = (rnd() % 512) - 256;
> -
>      qmul = rnd() % 4096;
>  
>      for (i = 0; i < FF_ARRAY_ELEMS(depths); i++) {
>          bit_depth = depths[i];
>          ff_h264dsp_init(&h, bit_depth, 1);
>  
> +        if (bit_depth == 8) {
> +            for (int j = 0; j < 16; j++)
> +                src[j] = (rnd() % 512) - 256;
> +        } else {
> +            int32_t *p = (int32_t *)src;
> +            for (int j = 0; j < 16; j++)
> +                p[j] = (rnd() % (1 << (bit_depth + 1))) - (1 << bit_depth);

This is an effective type violation and therefore UB. Furthermore,
increasing the size of the array has the downside that stack overflows
in the 8 bit codepath may go undetected. So better add a
LOCAL_ALIGNED_16(int32_t, src32, [16]) and use that for the >8 bit tests.

> +        }
> +
>          memset(dst0, 0, 16 * 16 * SIZEOF_COEF);
>          memset(dst1, 0, 16 * 16 * SIZEOF_COEF);
>  

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