From 4225f51c62b69f12e51151c2c73245342890f794 Mon Sep 17 00:00:00 2001
From: Leo Izen <leo.izen@gmail.com>
Date: Fri, 12 Jul 2024 15:03:16 -0400
Subject: [PATCH] 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@gmail.com>
Reported-by: Ramiro Polla <ramiro.polla@gmail.com>
Reviewed-by: Marton Balint <cus@passwd.hu>
---
 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;