Fix #383 (amendment)

When reading images in GD or GD2 format, we have to ensure that the
transparent color is not set, if it would refer to a non-extant palette
entry.

We back that up with respective regression tests.

src/gd_gd.c

@@ -108,10 +108,10 @@ _gdGetColors (gdIOCtx * in, gdImagePtr im, int gd2xFlag)
 		if (!gdGetWord (&im->transparent, in)) {
 			goto fail1;
 		}
-		/* Make sure transparent index is within bounds of the palette. */
-		if (im->transparent >= 256 || im->transparent < 0) {
-			im->transparent = (-1);
-		}
+	}
+	/* Make sure transparent index is within bounds of the palette. */
+	if (!(im->trueColor) && (im->transparent >= im->colorsTotal || im->transparent < 0)) {
+		im->transparent = (-1);
 	}
 	GD2_DBG (printf
 	         ("Palette had %d colours (T=%d)\n", im->colorsTotal,

tests/gd/.gitignore

@@ -1,3 +1,4 @@
+/bug00383
 /gd_im2im
 /gd_null
 /gd_num_colors

tests/gd/CMakeLists.txt

@@ -4,6 +4,7 @@ LIST(APPEND TESTS_FILES
 
 IF(ENABLE_GD_FORMATS)
 LIST(APPEND TESTS_FILES
+	bug00383
 	gd_null
 	gd_num_colors
 )

tests/gd/Makemodule.am

@@ -3,6 +3,7 @@ libgd_test_programs += \
 
 if ENABLE_GD_FORMATS
 libgd_test_programs += \
+    gd/bug00383 \
 	gd/gd_null \
 	gd/gd_num_colors
 

tests/gd/bug00383.c

@@ -0,0 +1,32 @@
+/**
+ * Test that invalid transparent colors can't be read
+ * 
+ * We're reading a corrupt palette image in GD format, which has only a single
+ * palette entry, but claims that the transparent color would be 1.  We check
+ * that the transparency is simply ignored in this case.
+ * 
+ * See also <https://github.com/libgd/libgd/issues/383>
+ */
+
+
+#include "gd.h"
+#include "gdtest.h"
+
+
+int main()
+{
+    gdImagePtr im;
+    FILE *fp;
+
+    fp = gdTestFileOpen2("gd", "bug00383.gd");
+    gdTestAssert(fp != NULL);
+    im = gdImageCreateFromGd(fp);
+    gdTestAssert(im != NULL);
+    fclose(fp);
+
+    gdTestAssert(gdImageGetTransparent(im) == -1);
+
+    gdImageDestroy(im);
+
+    return gdNumFailures();
+}

tests/gd2/.gitignore

@@ -2,6 +2,7 @@
 /bug00209
 /bug00309
 /bug00354
+/bug00383
 /gd2_empty_file
 /gd2_im2im
 /gd2_null

tests/gd2/CMakeLists.txt

@@ -5,6 +5,7 @@ LIST(APPEND TESTS_FILES
 	bug00209
 	bug00309
 	bug00354
+	bug00383
 	gd2_empty_file
 	php_bug_72339
 	gd2_null

tests/gd2/Makemodule.am

@@ -5,6 +5,7 @@ libgd_test_programs += \
 	gd2/bug00209 \
 	gd2/bug00309 \
 	gd2/bug00354 \
+	gd2/bug00383 \
 	gd2/gd2_empty_file \
 	gd2/php_bug_72339 \
 	gd2/gd2_null \

tests/gd2/bug00383.c

@@ -0,0 +1,32 @@
+/**
+ * Test that invalid transparent colors can't be read
+ * 
+ * We're reading a corrupt palette image in GD2 format, which has only a single
+ * palette entry, but claims that the transparent color would be 1.  We check
+ * that the transparency is simply ignored in this case.
+ * 
+ * See also <https://github.com/libgd/libgd/issues/383>
+ */
+
+
+#include "gd.h"
+#include "gdtest.h"
+
+
+int main()
+{
+    gdImagePtr im;
+    FILE *fp;
+
+    fp = gdTestFileOpen2("gd2", "bug00383.gd2");
+    gdTestAssert(fp != NULL);
+    im = gdImageCreateFromGd2(fp);
+    gdTestAssert(im != NULL);
+    fclose(fp);
+
+    gdTestAssert(gdImageGetTransparent(im) == -1);
+
+    gdImageDestroy(im);
+
+    return gdNumFailures();
+}