From 1a6c109c99a634e51cef645c524a2f2a2acf1cdf Mon Sep 17 00:00:00 2001
From: James Zern <jzern@google.com>
Date: Mon, 8 Aug 2022 16:40:21 -0700
Subject: [PATCH] WebPPictureHasTransparency: add missing pointer check

in the case of use_argb, alpha_offset may be non-zero which would cause
the null pointer check in CheckNonOpaque to pass

fixes a potential crash with invalid width/height set or an integer
sanitizer warning when passing a zeroed picture:
src/enc/picture_csp_enc.c:73:57: runtime error: applying non-zero offset
3 to null pointer

Change-Id: I9d499bba12c65ad5c65d8f9f3c8ee9298ac6081a
---
 src/enc/picture_csp_enc.c | 9 ++++++---
 1 file changed, 6 insertions(+), 3 deletions(-)

diff --git a/src/enc/picture_csp_enc.c b/src/enc/picture_csp_enc.c
index fabebcf2..d23ac776 100644
--- a/src/enc/picture_csp_enc.c
+++ b/src/enc/picture_csp_enc.c
@@ -70,9 +70,12 @@ int WebPPictureHasTransparency(const WebPPicture* picture) {
   if (picture == NULL) return 0;
   if (picture->use_argb) {
     const int alpha_offset = ALPHA_OFFSET;
-    return CheckNonOpaque((const uint8_t*)picture->argb + alpha_offset,
-                          picture->width, picture->height,
-                          4, picture->argb_stride * sizeof(*picture->argb));
+    if (picture->argb != NULL) {
+      return CheckNonOpaque((const uint8_t*)picture->argb + alpha_offset,
+                            picture->width, picture->height,
+                            4, picture->argb_stride * sizeof(*picture->argb));
+    }
+    return 0;
   }
   return CheckNonOpaque(picture->a, picture->width, picture->height,
                         1, picture->a_stride);