[FFmpeg-cvslog] avcodec/pngdec: avoid erroring with sBIT on indexed-color images

[Leo Izen]

ffmpeg | branch: master | Leo Izen <leo.izen at gmail.com> | Fri Jul 12 15:03:16 2024 -0400| [4225f51c62b69f12e51151c2c73245342890f794] | committer: Leo Izen

avcodec/pngdec: avoid erroring with sBIT on indexed-color images

Indexed color images use three colors for sBIT, but the function
ff_png_get_nb_channels returns 1 in this case. We should avoid erroring
out on valid files in this scenario.

Regression since 84b454935fae2633a8a5dd075e22393f3e8f932f.

Signed-off-by: Leo Izen <leo.izen at gmail.com>
Reported-by: Ramiro Polla <ramiro.polla at gmail.com>
Reviewed-by: Marton Balint <cus at passwd.hu>

> http://git.videolan.org/gitweb.cgi/ffmpeg.git/?a=commit;h=4225f51c62b69f12e51151c2c73245342890f794
---

 libavcodec/pngdec.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/libavcodec/pngdec.c b/libavcodec/pngdec.c
index 180806e5e1..b0d02c97dd 100644
--- a/libavcodec/pngdec.c
+++ b/libavcodec/pngdec.c
@@ -1084,7 +1084,7 @@ static int decode_sbit_chunk(AVCodecContext *avctx, PNGDecContext *s,
         return AVERROR_INVALIDDATA;
     }
 
-    channels = ff_png_get_nb_channels(s->color_type);
+    channels = s->color_type & PNG_COLOR_MASK_PALETTE ? 3 : ff_png_get_nb_channels(s->color_type);
 
     if (bytestream2_get_bytes_left(gb) != channels)
         return AVERROR_INVALIDDATA;