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

[James Almer <jamrial@gmail.com>]

On 4/2/2024 12:30 AM, Andreas Rheinhardt wrote:
> 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)".

I misread the check, so there's nothing wrong with it. But I'll apply 
that suggestion of yours in any case since it's simpler than the current 
one.
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