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

[Filip Roséen]

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.
---
 modules/codec/lpcm.c | 14 ++++++++++++++
 1 file changed, 14 insertions(+)

diff --git a/modules/codec/lpcm.c b/modules/codec/lpcm.c
index 801f12e..b4dcad4 100644
--- a/modules/codec/lpcm.c
+++ b/modules/codec/lpcm.c
@@ -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 );
+
+        if( block_nb_frames > aout_nb_frames )
+        {
+            msg_Warn( p_dec, "invalid block size" );
+
+            block_Release( p_block );
+            block_Release( p_aout_buffer );
+
+            return NULL;
+        }
+
         switch( p_sys->i_type )
         {
         case LPCM_WIDI:
-- 
2.10.2