[FFmpeg-devel] [PATCH] apng: use correct size for output buffer

[Andreas Cadhalpun]

This fixes a stack buffer overflow.

Signed-off-by: Andreas Cadhalpun <Andreas.Cadhalpun at googlemail.com>
---
 libavcodec/pngdec.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/libavcodec/pngdec.c b/libavcodec/pngdec.c
index 689aa2b..c974654 100644
--- a/libavcodec/pngdec.c
+++ b/libavcodec/pngdec.c
@@ -1010,13 +1010,13 @@ static int handle_p_frame_apng(AVCodecContext *avctx, PNGDecContext *s,
             memcpy(buffer + row_start, p->data[0] + row_start, s->bpp * s->cur_w);
         }
     } else { // APNG_BLEND_OP_OVER
+        uint8_t *output = av_malloc(s->bpp);
         for (y = s->y_offset; y < s->y_offset + s->cur_h; ++y) {
             uint8_t *foreground = p->data[0] + s->image_linesize * y + s->bpp * s->x_offset;
             uint8_t *background = buffer + s->image_linesize * y + s->bpp * s->x_offset;
             for (x = s->x_offset; x < s->x_offset + s->cur_w; ++x, foreground += s->bpp, background += s->bpp) {
                 size_t b;
                 uint8_t foreground_alpha, background_alpha, output_alpha;
-                uint8_t output[4];
 
                 // Since we might be blending alpha onto alpha, we use the following equations:
                 // output_alpha = foreground_alpha + (1 - foreground_alpha) * background_alpha
@@ -1069,6 +1069,7 @@ static int handle_p_frame_apng(AVCodecContext *avctx, PNGDecContext *s,
                 memcpy(background, output, s->bpp);
             }
         }
+        av_freep(&output);
     }
 
     // Copy blended buffer into the frame and free
-- 
2.6.1