[FFmpeg-devel] [PATCH] avcodec/htmlsubtitles: Be a bit more picky on syntax

[wm4]

On Sun,  2 Jul 2017 00:09:42 +0200
Michael Niedermayer <michael at niedermayer.cc> wrote:

> This reduces the number of strstr() calls per byte
> This diasalows empty tags like '< >' as well as '<' in tags like '<ab<cd<<ef>'
> 
> Fixes timeout
> Fixes: 1817/clusterfuzz-testcase-minimized-5104230530547712
> 
> Found-by: continuous fuzzing process https://github.com/google/oss-fuzz/tree/master/projects/ffmpeg
> Signed-off-by: Michael Niedermayer <michael at niedermayer.cc>
> ---
>  libavcodec/htmlsubtitles.c | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/libavcodec/htmlsubtitles.c b/libavcodec/htmlsubtitles.c
> index be5c9316ca..67abc94085 100644
> --- a/libavcodec/htmlsubtitles.c
> +++ b/libavcodec/htmlsubtitles.c
> @@ -110,13 +110,13 @@ int ff_htmlmarkup_to_ass(void *log_ctx, AVBPrint *dst, const char *in)
>          case '<':
>              tag_close = in[1] == '/';
>              len = 0;
> -            if (sscanf(in+tag_close+1, "%127[^>]>%n", buffer, &len) >= 1 && len > 0) {
> +            if (sscanf(in+tag_close+1, "%127[^<>]>%n", buffer, &len) >= 1 && len > 0) {
>                  const char *tagname = buffer;
>                  while (*tagname == ' ')
>                      tagname++;
>                  if ((param = strchr(tagname, ' ')))
>                      *param++ = 0;
> -                if ((!tag_close && sptr < FF_ARRAY_ELEMS(stack)) ||
> +                if ((!tag_close && sptr < FF_ARRAY_ELEMS(stack) && *tagname) ||
>                      ( tag_close && sptr > 0 && !strcmp(stack[sptr-1].tag, tagname))) {
>                      int i, j, unknown = 0;
>                      in += len + tag_close;

Invalid syntax is not unusual in SRT files. Are you sure this doesn't
make the output worse in files that do not use the syntax correctly?