Andreas Rheinhardt:
In my test case:
avformat_open_input(pInputContext, ...) returns an error code
Attempts to free the (allocated?) context memory then causes a NULL reference
exception when accessing &s->internal->id3v2_meta, etc. since &s->internal is
NULL.
avformat_free_context(pInputContext)
- Robert.
-----Original Message-----
From: ffmpeg-devel <ffmpeg-devel-boun...@ffmpeg.org> On Behalf Of Andreas
Rheinhardt
Sent: June 8, 2021 1:21 PM
To: ffmpeg-devel@ffmpeg.org
Subject: Re: [FFmpeg-devel] [PATCH] Null check of &s->internal before
attempting to free dict and pkt - avoid Null pointer dereference crash
Robert Beyer:
> ---
> libavformat/utils.c | 8 +++++---
> 1 file changed, 5 insertions(+), 3 deletions(-)
>
> diff --git a/libavformat/utils.c b/libavformat/utils.c
> index fe8eaa6cb3..73a7d13123 100644
> --- a/libavformat/utils.c
> +++ b/libavformat/utils.c
> @@ -4331,9 +4331,11 @@ void avformat_free_context(AVFormatContext *s)
> }
> av_freep(&s->chapters);
> av_dict_free(&s->metadata);
> - av_dict_free(&s->internal->id3v2_meta);
> - av_packet_free(&s->internal->pkt);
> - av_packet_free(&s->internal->parse_pkt);
> + if (&s->internal) {
> + av_dict_free(&s->internal->id3v2_meta);
> + av_packet_free(&s->internal->pkt);
> + av_packet_free(&s->internal->parse_pkt);
> + }
> av_freep(&s->streams);
> flush_packet_queue(s);
> av_freep(&s->internal);
>
1. Checking for &s->internal is nonsense: If s is not NULL and points to
an AVFormatContext, &s->internal is so, too. You want to check for
s->internal.
2. avformat_alloc_context() (the only function that directly allocates
AVFormatContexts) ensures that every successfully allocated
AVFormatContext has an AVFormatInternal set, so the issue should just
not happen. If it does happen for you, then please provide the necessary
details to reproduce it.
- Andreas
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