Re: [FFmpeg-devel] [PATCH 2/3] avformat/evcdec: Check that enough data has been read

[James Almer <jamrial@gmail.com>]

On 7/6/2023 10:14 PM, James Almer wrote:
> On 7/6/2023 6:08 PM, Andreas Rheinhardt wrote:
>> Fixes potential use of uninitialized values
>> in evc_read_nal_unit_length().
>>
>> Signed-off-by: Andreas Rheinhardt <andreas.rheinhardt@outlook.com>
>> ---
>>   libavformat/evcdec.c | 2 ++
>>   1 file changed, 2 insertions(+)
>>
>> diff --git a/libavformat/evcdec.c b/libavformat/evcdec.c
>> index 9886542311..0f464930f7 100644
>> --- a/libavformat/evcdec.c
>> +++ b/libavformat/evcdec.c
>> @@ -162,6 +162,8 @@ static int evc_read_packet(AVFormatContext *s, 
>> AVPacket *pkt)
>>           ret = avio_read(s->pb, buf, EVC_NALU_LENGTH_PREFIX_SIZE);
>>           if (ret < 0)
>>               return ret;
>> +        if (ret != EVC_NALU_LENGTH_PREFIX_SIZE)
>> +            return AVERROR_INVALIDDATA;
> 
> There's a ffio_ensure_seekback() for EVC_NALU_LENGTH_PREFIX_SIZE bytes 
> immediately before the avio_read() call. Shouldn't that be enough to 
> guarantee that much can be read?
> 
> Also, you can just pass ret to evc_read_nal_unit_length() below instead 
> of adding this check here. It will return an error if it's < 
> EVC_NALU_LENGTH_PREFIX_SIZE.

Oh, my bad, i was looking at the function of the same name in 
libavcodec/evc_parse.h

The function in evc.h could be changed to also use the same check as the 
one the evc_parse.h version alongside the other change you're doing in 
patch 3/3.

> 
>>           nalu_size = evc_read_nal_unit_length(buf, 
>> EVC_NALU_LENGTH_PREFIX_SIZE);
>>           if (!nalu_size || nalu_size > INT_MAX)
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