[FFmpeg-devel] [PATCH 1/3] avcodec/alsdec: Limit maximum channels to 64

[Thilo Borgmann]

Am 19.08.19 um 23:22 schrieb Michael Niedermayer:
> On Mon, Aug 19, 2019 at 05:09:37PM +0200, Thilo Borgmann wrote:
>> Am 19.08.19 um 14:27 schrieb Michael Niedermayer:
>>> On Mon, Aug 19, 2019 at 07:41:43AM +0200, Thilo Borgmann wrote:
>>>> Am 19.08.19 um 01:30 schrieb Michael Niedermayer:
>>>>> There seems to be no limit in the specification and upto 64k could be stored
>>>>> 64 is chooses as limit as thats also used for AAC and is what a int64 mask
>>>>> can handle
>>>>>
>>>>> An alternative to this patch would be a max_channels variable
>>>>
>>>> There's a conformance file containing 512 channels, that should be the default max value.
>>>
>>> will apply with that value later
>>
>> Decoding of that is already stopped via FF_SANE_NB_CHANNELS in lavc/internal.h.
>> That is currently set to 256U. I guess pushing that to 512U might already be enough without any change to single decoders?
> 
> the problem of out of memory is that the als decoder allocates some pretty
> large things per channel. A check on channels needs to happen before
> this.
> The existing checks didnt achieve that.
> 
> I can of course post a patchset that uses FF_SANE_NB_CHANNELS in als and
> bump it to the next number if people prefer this ?
> 
> Note though that increasing FF_SANE_NB_CHANNELS may also increase timeouts
> in other decoders.

I see the problem.
However, right now alsdec is fine with any number of channels and the CLI prevents decoding anything above FF_SANE_NB_CHANNELS (checks are in lavc/decoding.c and lavc/utils.c; this would also stop any FATE test on 512 channels file).

So having alsdec check for a value higher than FF_SANE_NB_CHANNELS (like 512) would have no effect for CLI users, right?

-Thilo

>> Once fixed, I will add a FATE test for the 512 channel conformance file.
> 
> thx
> 
>>
>> -Thilo
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