[FFmpeg-devel] [PATCH 4/4] avformat/mov: Stash mfra size if we're reading it anyway

[James Almer]

On 9/1/2020 12:03 PM, Derek Buitenhuis wrote:
> This also changes a check for mfra_size from < 0 to == 0, since
> it was always wrong, as avio_rb32 returns an unsigned integer.

mfra_size in this function was an int32_t, so storing the output of
avio_rb32() could end up with a negative value.
It'll no longer be the case now that you made mfra_size in MOVContext an
uint32_t.

> 
> Signed-off-by: Derek Buitenhuis <derek.buitenhuis at gmail.com>
> ---
>  libavformat/mov.c | 10 +++++-----
>  1 file changed, 5 insertions(+), 5 deletions(-)
> 
> diff --git a/libavformat/mov.c b/libavformat/mov.c
> index e33031f158..e901eb527f 100644
> --- a/libavformat/mov.c
> +++ b/libavformat/mov.c
> @@ -7499,22 +7499,22 @@ static int mov_read_mfra(MOVContext *c, AVIOContext *f)
>      int64_t stream_size = avio_size(f);
>      int64_t original_pos = avio_tell(f);
>      int64_t seek_ret;
> -    int32_t mfra_size;
>      int ret = -1;
>      if ((seek_ret = avio_seek(f, stream_size - 4, SEEK_SET)) < 0) {
>          ret = seek_ret;
>          goto fail;
>      }
> -    mfra_size = avio_rb32(f);
> -    if (mfra_size < 0 || mfra_size > stream_size) {
> +    c->mfra_size = avio_rb32(f);
> +    c->have_read_mfra_size = 1;
> +    if (c->mfra_size == 0 || c->mfra_size > stream_size) {

nit: !c->mfra_size.

>          av_log(c->fc, AV_LOG_DEBUG, "doesn't look like mfra (unreasonable size)\n");
>          goto fail;
>      }
> -    if ((seek_ret = avio_seek(f, -mfra_size, SEEK_CUR)) < 0) {
> +    if ((seek_ret = avio_seek(f, -c->mfra_size, SEEK_CUR)) < 0) {

You may have to cast c->mfra_size to int64_t before negating it, or use
a local int64_t variable.

>          ret = seek_ret;
>          goto fail;
>      }
> -    if (avio_rb32(f) != mfra_size) {
> +    if (avio_rb32(f) != c->mfra_size) {
>          av_log(c->fc, AV_LOG_DEBUG, "doesn't look like mfra (size mismatch)\n");
>          goto fail;
>      }
>