[FFmpeg-cvslog] avcodec/imgconvert: fix possible null pointer dereference

[Simon Thelen]

ffmpeg | branch: release/3.4 | Simon Thelen <ffmpeg-dev at c-14.de> | Tue Apr  3 14:41:33 2018 +0200| [c1e172c2e14ef059dac632f7c67f081dfecd30dc] | committer: Jan Ekström

avcodec/imgconvert: fix possible null pointer dereference

regression since 354b26a3945eadd4ed8fcd801dfefad2566241de

(cherry picked from commit 8c2c97403baf95d0facb53f03e468f023eb943e1)

> http://git.videolan.org/gitweb.cgi/ffmpeg.git/?a=commit;h=c1e172c2e14ef059dac632f7c67f081dfecd30dc
---

 libavcodec/imgconvert.c | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/libavcodec/imgconvert.c b/libavcodec/imgconvert.c
index 7b0005b308..1fd636c83d 100644
--- a/libavcodec/imgconvert.c
+++ b/libavcodec/imgconvert.c
@@ -72,11 +72,12 @@ enum AVPixelFormat avcodec_find_best_pix_fmt_of_list(const enum AVPixelFormat *p
     int loss;
 
     for (i=0; pix_fmt_list[i] != AV_PIX_FMT_NONE; i++) {
-        loss = *loss_ptr;
+        loss = loss_ptr ? *loss_ptr : 0;
         best = avcodec_find_best_pix_fmt_of_2(best, pix_fmt_list[i], src_pix_fmt, has_alpha, &loss);
     }
 
-    *loss_ptr = loss;
+    if (loss_ptr)
+        *loss_ptr = loss;
     return best;
 }