[vlc-devel] [RFC] codec/lpcm: drop blocks with invalid size

[Francois Cartegnie]

Le 07/12/2016 à 13:35, Filip Roséen a écrit :
> These changes prevent a heap-buffer overflow where the block header
> indicates that the block is different than what it actually should be
> (given the output-format used within decoder_NewAudioBuffer).
> 
> In short, blocks that are too large to fit into the audio-buffer will
> be discarded. Prior to these changes the entire contents would be
> parsed, leading to undefined-behavior further down the road.

If there's an issue (and I don't see how it happens since sample number
is computed from block size, aout format updated and then buffer
allocated ) the fix is not a post alloc check.

> @@ -468,6 +468,20 @@ static block_t *DecodeFrame( decoder_t *p_dec, block_t **pp_block )
>          p_block->p_buffer += p_sys->i_header_size + i_padding;
>          p_block->i_buffer -= p_sys->i_header_size + i_padding;
>  
> +        const unsigned block_nb_frames = p_block->i_buffer / ( i_bits * 4 / 8 );
> +        const unsigned aout_nb_frames = p_aout_buffer->i_nb_samples
> +            / ( p_dec->fmt_out.audio.i_bitspersample / 8 );
> +

This is incorrect, and breaks BD LPCM for even channels number.


Francois