Re: [FFmpeg-devel] [PATCH 3/6] avformat/aviobuf: Don't use NULL as src for memcpy

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

James Almer:
> On 9/28/2022 3:58 PM, Andreas Rheinhardt wrote:
>> This might happen in avio_write() if size == 0
>> when the direct codepath is taken. It is undefined behaviour
>> according to the spec although it happens to work in practice.
>> Fixes the webm-webvtt-remux FATE-test under UBSan.
>>
>> Signed-off-by: Andreas Rheinhardt <andreas.rheinhardt@outlook.com>
>> ---
>>   libavformat/aviobuf.c | 4 +++-
>>   1 file changed, 3 insertions(+), 1 deletion(-)
>>
>> diff --git a/libavformat/aviobuf.c b/libavformat/aviobuf.c
>> index b20b1a611a..5b6a42d7f4 100644
>> --- a/libavformat/aviobuf.c
>> +++ b/libavformat/aviobuf.c
>> @@ -231,6 +231,8 @@ void ffio_fill(AVIOContext *s, int b, int64_t count)
>>     void avio_write(AVIOContext *s, const unsigned char *buf, int size)
>>   {
>> +    if (size <= 0)
>> +        return;
>>       if (s->direct && !s->update_checksum) {
>>           avio_flush(s);
>>           writeout(s, buf, size);
>> @@ -246,7 +248,7 @@ void avio_write(AVIOContext *s, const unsigned
>> char *buf, int size)
>>             buf += len;
>>           size -= len;
>> -    }
>> +    } while (size > 0);
> 
> Why are you adding this at the end of a similar while statement? Did you
> mean to replace the previous one with do()?
> 

Yes, exactly. Somehow I didn't. fate passed locally (apart from the
tdsc). Crazy that I forgot this. Thanks for spotting.

- Andreas

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