[FFmpeg-devel] [PATCH 1/4] avutil/avstring: Fix bug and undefined behavior in av_strncasecmp()

[Paul B Mahol]

On 4/16/19, Michael Niedermayer <michael at niedermayer.cc> wrote:
> The function in case of n=0 would read more bytes than 0.
> The end pointer could be beyond the allocated space, which
> is undefined.
>
> Signed-off-by: Michael Niedermayer <michael at niedermayer.cc>
> ---
>  libavutil/avstring.c | 5 +++--
>  1 file changed, 3 insertions(+), 2 deletions(-)
>
> diff --git a/libavutil/avstring.c b/libavutil/avstring.c
> index f03dd25141..4c068f5bc5 100644
> --- a/libavutil/avstring.c
> +++ b/libavutil/avstring.c
> @@ -222,12 +222,13 @@ int av_strcasecmp(const char *a, const char *b)
>
>  int av_strncasecmp(const char *a, const char *b, size_t n)
>  {
> -    const char *end = a + n;
>      uint8_t c1, c2;
> +    if (n <= 0)
> +        return 0;
>      do {
>          c1 = av_tolower(*a++);
>          c2 = av_tolower(*b++);
> -    } while (a < end && c1 && c1 == c2);
> +    } while (--n && c1 && c1 == c2);
>      return c1 - c2;
>  }
>
> --
> 2.21.0
>

LGTM

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