Re: [FFmpeg-devel] [PATCH v1] avformat/imf: fix bad free() when directory name of the input url is empty

[Pierre-Anthony Lemieux <pal@sandflow.com>]

On Tue, Jan 4, 2022 at 5:39 PM Zane van Iperen <zane@zanevaniperen.com> wrote:
>
>
>
> On 4/1/22 01:59, pal@sandflow.com wrote:
> > From: Pierre-Anthony Lemieux <pal@palemieux.com>
> >
> > Signed-off-by: Pierre-Anthony Lemieux <pal@palemieux.com>
> > ---
> >
> > Notes:
> >      Found through manual fuzzing.
> >
> >   libavformat/imfdec.c | 6 +++++-
> >   1 file changed, 5 insertions(+), 1 deletion(-)
> >
> > diff --git a/libavformat/imfdec.c b/libavformat/imfdec.c
> > index f17064cfcd..4e42db8d30 100644
> > --- a/libavformat/imfdec.c
> > +++ b/libavformat/imfdec.c
> > @@ -622,11 +622,15 @@ static int imf_read_header(AVFormatContext *s)
> >       int ret = 0;
> >
> >       c->interrupt_callback = &s->interrupt_callback;
> > +
> >       tmp_str = av_strdup(s->url);
> >       if (!tmp_str)
> >           return AVERROR(ENOMEM);
> > +    c->base_url = av_strdup(av_dirname(tmp_str));
>
> Is the second av_strdup() here required? You've already done it above
> and av_dirname() just sticks a '\0' at the last separator,

This is what I thought.

> so it should
> be safe to remove it:

As I understand it, av_dirname() actually returns a pointer to its own
"." string when the input is either empty or does not contain, in
which case we must make a copy.

>
>    if (!(c->base_url = av_strdup(s->url)))
>        return AVERROR(ENOMEM);
>
>    c->base_url = av_dirname(c->base_url);
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