[FFmpeg-devel] [PATCH 2/3] avformat/swfdec: Reorder allocations/initializations

[Andreas Rheinhardt]

Andreas Rheinhardt:
> The earlier code would first attempt to allocate two buffers, then
> attempt to allocate an AVIOContext, using one of the new buffers I/O
> buffer, then check the allocations. On success, a z_stream that is used
> in the AVIOContext's read_packet callback is initialized afterwards.
> 
> There are two problems with this: In case the allocation of the I/O
> buffer fails avio_alloc_context() will be given a NULL read buffer
> with a size > 0. This works right now, but it is fragile. The second
> problem is that the z_stream used in the read_packet callback is not
> functional when avio_alloc_context() is allocated (it might be that
> avio_alloc_context() might already fill the buffer in the future). This
> commit fixes both of these problems by reordering the operations.
> 
> Signed-off-by: Andreas Rheinhardt <andreas.rheinhardt at gmail.com>
> ---
>  libavformat/swfdec.c | 24 ++++++++++--------------
>  1 file changed, 10 insertions(+), 14 deletions(-)
> 
> diff --git a/libavformat/swfdec.c b/libavformat/swfdec.c
> index 7a74fa3ac7..d1ed1e2a53 100644
> --- a/libavformat/swfdec.c
> +++ b/libavformat/swfdec.c
> @@ -128,6 +128,8 @@ retry:
>  
>      return buf_size - z->avail_out;
>  }
> +
> +static av_cold int swf_read_close(AVFormatContext *avctx);
>  #endif
>  
>  static int swf_read_header(AVFormatContext *s)
> @@ -142,24 +144,18 @@ static int swf_read_header(AVFormatContext *s)
>      if (tag == MKBETAG('C', 'W', 'S', 0)) {
>          av_log(s, AV_LOG_INFO, "SWF compressed file detected\n");
>  #if CONFIG_ZLIB
> -        swf->zbuf_in  = av_malloc(ZBUF_SIZE);
> -        swf->zbuf_out = av_malloc(ZBUF_SIZE);
> -        swf->zpb = avio_alloc_context(swf->zbuf_out, ZBUF_SIZE, 0, s,
> -                                      zlib_refill, NULL, NULL);
> -        if (!swf->zbuf_in || !swf->zbuf_out || !swf->zpb) {
> -            av_freep(&swf->zbuf_in);
> -            av_freep(&swf->zbuf_out);
> -            avio_context_free(&swf->zpb);
> -            return AVERROR(ENOMEM);
> -        }
> -        swf->zpb->seekable = 0;
>          if (inflateInit(&swf->zstream) != Z_OK) {
>              av_log(s, AV_LOG_ERROR, "Unable to init zlib context\n");
> -            av_freep(&swf->zbuf_in);
> -            av_freep(&swf->zbuf_out);
> -            avio_context_free(&swf->zpb);
>              return AVERROR(EINVAL);
>          }
> +        if (!(swf->zbuf_in  = av_malloc(ZBUF_SIZE)) ||
> +            !(swf->zbuf_out = av_malloc(ZBUF_SIZE)) ||
> +            !(swf->zpb = avio_alloc_context(swf->zbuf_out, ZBUF_SIZE, 0,
> +                                            s, zlib_refill, NULL, NULL))) {
> +            swf_read_close(s);
> +            return AVERROR(ENOMEM);
> +        }
> +        swf->zpb->seekable = 0;
>          pb = swf->zpb;
>  #else
>          av_log(s, AV_LOG_ERROR, "zlib support is required to read SWF compressed files\n");
> 
Will apply.

- Andreas