On Fri, 4 Jul 2025 at 20:22, Andreas Rheinhardt
<andreas.rheinha...@outlook.com> wrote:
>
> Kacper Michajłow:
> > av_get_token() allocates an output buffer with the same size as the
> > input. Generally, this is harmless, but when the input string is large
> > and consists of many small tokens, calling av_get_token() repeatedly to
> > extract all tokens will significantly amplify memory allocations.
> >
> > To fix this, after obtaining the return value, simply realloc the buffer
> > to the actual size needed for output string.
> >
> > Fixes OOM when parsing filter graph string.
> > Fixes OSS-Fuzz: 394983446
> >
> > Signed-off-by: Kacper Michajłow <kaspe...@gmail.com>
> > ---
> > libavutil/avstring.c | 4 ++--
> > 1 file changed, 2 insertions(+), 2 deletions(-)
> >
> > diff --git a/libavutil/avstring.c b/libavutil/avstring.c
> > index 875eb691db..b4266aefe5 100644
> > --- a/libavutil/avstring.c
> > +++ b/libavutil/avstring.c
> > @@ -142,7 +142,7 @@ end:
> >
> > char *av_get_token(const char **buf, const char *term)
> > {
> > - char *out = av_malloc(strlen(*buf) + 1);
> > + char *out = av_realloc(NULL, strlen(*buf) + 1);
>
> I thought pointers provided by av_malloc could be used with
> av_realloc()? Or is it to avoid the unnecessary alignment provided by
> av_malloc()?
I was thinking about this. But the docs, of av_realloc() say
* @param ptr Pointer to a memory block already allocated with
* av_realloc() or `NULL`
so to honor this, I changed to av_realloc(NULL). I've looked at other
uses and it seems to be a pattern that is used for cases like this
one.
> > char *ret = out, *end = out;
> > const char *p = *buf;
> > if (!out)
> > @@ -172,7 +172,7 @@ char *av_get_token(const char **buf, const char *term)
> >
> > *buf = p;
> >
> > - return ret;
> > + return av_realloc(ret, out - ret + 2);
>
> You seem to presume that av_realloc() can't fail when used for
> shrinking. But this is not documented.
This function returns a pointer. So if it fails, returning NULL is
valid. Unless you mean that we add another possible point of failure?
I don't think it matters, if we are already close to OOM state, this
small alloc wouldn't be a difference maker.
- Kacper
> > }
> >
> > char *av_strtok(char *s, const char *delim, char **saveptr)
>
> _______________________________________________
> ffmpeg-devel mailing list
> ffmpeg-devel@ffmpeg.org
> https://ffmpeg.org/mailman/listinfo/ffmpeg-devel
>
> To unsubscribe, visit link above, or email
> ffmpeg-devel-requ...@ffmpeg.org with subject "unsubscribe".
_______________________________________________
ffmpeg-devel mailing list
ffmpeg-devel@ffmpeg.org
https://ffmpeg.org/mailman/listinfo/ffmpeg-devel
To unsubscribe, visit link above, or email
ffmpeg-devel-requ...@ffmpeg.org with subject "unsubscribe".
