Re: [FFmpeg-devel] [PATCH 3/3] avformat/mov: fix the entry count overflow check in the keys atom

[Andreas Rheinhardt <andreas.rheinhardt@outlook.com>]

James Almer:
> Signed-off-by: James Almer <jamrial@gmail.com>
> ---
>  libavformat/mov.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/libavformat/mov.c b/libavformat/mov.c
> index a935ef7326..9fca402896 100644
> --- a/libavformat/mov.c
> +++ b/libavformat/mov.c
> @@ -5025,7 +5025,7 @@ static int mov_read_keys(MOVContext *c, AVIOContext *pb, MOVAtom atom)
>      avio_skip(pb, 4);
>      count = avio_rb32(pb);
>      atom.size -= 8;
> -    if (count > UINT_MAX / sizeof(*c->meta_keys) - 1) {
> +    if (count + 1LL > UINT_MAX / sizeof(*c->meta_keys)) {
>          av_log(c->fc, AV_LOG_ERROR,
>                 "The 'keys' atom with the invalid key count: %"PRIu32"\n", count);
>          return AVERROR_INVALIDDATA;

What is supposed to be wrong here in the first place? The only thing I
can think of is the case in which sizeof(*c->meta_keys) is > UINT_MAX,
in which case the rhs would wrap around. But I don't think that is what
you meant given that sizeof(*c->meta_keys) == sizeof(char*).
Anyway, a simpler check that works even if sizeof(*c->meta_keys) were
insanely large is "count >= UINT_MAX / sizeof(*c->meta_keys)".

- Andreas

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