[FFmpeg-devel] [PATCH 2/7] avutil/bprint: Allow size == 0 in av_bprint_init_for_buffer()

[Andreas Rheinhardt]

James Almer:
> On 8/9/2023 7:08 AM, Nicolas George wrote:
>> Andreas Rheinhardt (12023-08-06):
>>> The AVBPrint API guarantees that the string buffer is always
>>> zero-terminated; in order to honour this guarantee, there
>>> obviously must be a string buffer at all and it must have
>>> a size >= 1. Therefore av_bprint_init_for_buffer() treats
>>> passing a NULL buffer or size == 0 as invalid data that
>>> leads to undefined behaviour, namely NPD in case NULL is provided
>>> or a write to a buffer of size 0 in case size == 0.
>>>
>>> But it would be easy to support this, namely by using the internal
>>> buffer with AV_BPRINT_SIZE_COUNT_ONLY in case size == 0.
>>>
>>> There is a reason to allow this: Several functions like
>>> av_channel_(description|name) are actually wrappers
>>> around corresponding AVBPrint functions. They accept user
>>> provided buffers and are supposed to return the required
>>> size of the buffer, which would allow the user to call
>>> it once to get the required buffer size and call it once
>>> more after having allocated the buffer.
>>> If av_bprint_init_for_buffer() treats size == 0 as invalid,
>>> all these users would need to check for this themselves
>>> and basically add the same codeblock that this patch
>>> adds to av_bprint_init_for_buffer().
>>>
>>> This change is in line with e.g. snprintf() which also allows
>>> the pointer to be NULL in case size is zero.
>>>
>>> This fixes Coverity issues #1503074, #1503076 and #1503082;
>>> all of these issues are about providing NULL to the channel-layout
>>> functions that are wrappers around AVBPrint versions.
>>>
>>> Signed-off-by: Andreas Rheinhardt <andreas.rheinhardt at outlook.com>
>>> ---
>>> Missing lavu minor version bump.
>>
>> Looks good to me.
>>
>> The other patches in the series too, but I do not maintain the channel
>> layouts.
>>
>> Regards,
> 
> The layout patches are ok too.

Ok, then I'll already apply them tomorrow. Thanks for the reviews.

- Andreas