[FFmpeg-devel] [PATCH 1/2] avcodec/movtextenc: Check for too many styles

[Guo, Yejun]

> -----Original Message-----
> From: ffmpeg-devel <ffmpeg-devel-bounces at ffmpeg.org> On Behalf Of
> Andreas Rheinhardt
> Sent: 2021年2月21日 9:41
> To: ffmpeg-devel at ffmpeg.org
> Cc: Andreas Rheinhardt <andreas.rheinhardt at gmail.com>
> Subject: [FFmpeg-devel] [PATCH 1/2] avcodec/movtextenc: Check for too many
> styles
> 
> The counter for the number of styles is written on two bytes, ergo anything >
> UINT16_MAX is invalid. This also fixes a compiler warning because of a
> tautologically true check on 64bit systems.
> 
> Signed-off-by: Andreas Rheinhardt <andreas.rheinhardt at gmail.com>
> ---
> A better solution would be to error out as soon as the byte length of a subtitle
> exceeds UINT16_MAX; yet for this one would have to modify all of ass_split to
> allow the callbacks to return errors.
> 
>  libavcodec/movtextenc.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/libavcodec/movtextenc.c b/libavcodec/movtextenc.c index
> 1bef21e0b9..cf30adbd0a 100644
> --- a/libavcodec/movtextenc.c
> +++ b/libavcodec/movtextenc.c
> @@ -355,7 +355,7 @@ static int mov_text_style_start(MovTextContext *s)
>          StyleBox *tmp;
> 
>          // last style != defaults, end the style entry and start a new one
> -        if (s->count + 1 > SIZE_MAX / sizeof(*s->style_attributes) ||
> +        if (s->count + 1 > FFMIN(SIZE_MAX /
> + sizeof(*s->style_attributes), UINT16_MAX) ||

hi, logically, I think the result of FFMIN(SIZE_MAX / sizeof(*s->style_attributes), UINT16_MAX) is always UINT16_MAX, we may just use 's->count + 1 > UINT16_MAX'.


>              !(tmp = av_fast_realloc(s->style_attributes,
> 
> &s->style_attributes_bytes_allocated,
>                                      (s->count + 1) *
> sizeof(*s->style_attributes)))) {
> --
> 2.27.0
> 
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