[FFmpeg-cvslog] avcodec/pngdec: Don't use unsigned for width, height

[Andreas Rheinhardt]

ffmpeg | branch: master | Andreas Rheinhardt <andreas.rheinhardt at outlook.com> | Thu Sep 29 01:45:23 2022 +0200| [042c1966da4dfb95a3d8adc3358d16bb99a21282] | committer: Andreas Rheinhardt

avcodec/pngdec: Don't use unsigned for width, height

Otherwise p->linesize[0] * y will be evaluated as an unsigned
which leads to segfaults in case linesize is negative.
This happens in the apng-dispose-previous FATE-test in case
one makes get_buffer return pictures with negative linesizes.

Signed-off-by: Andreas Rheinhardt <andreas.rheinhardt at outlook.com>

> http://git.videolan.org/gitweb.cgi/ffmpeg.git/?a=commit;h=042c1966da4dfb95a3d8adc3358d16bb99a21282
---

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

diff --git a/libavcodec/pngdec.c b/libavcodec/pngdec.c
index 582953d17b..3c3eca601e 100644
--- a/libavcodec/pngdec.c
+++ b/libavcodec/pngdec.c
@@ -1387,7 +1387,7 @@ exit_loop:
     if (s->has_trns && s->color_type != PNG_COLOR_TYPE_PALETTE) {
         size_t byte_depth = s->bit_depth > 8 ? 2 : 1;
         size_t raw_bpp = s->bpp - byte_depth;
-        unsigned x, y;
+        ptrdiff_t x, y;
 
         av_assert0(s->bit_depth > 1);