Fix #492: Potential double-free in gdImage*Ptr()

Whenever `gdImage*Ptr()` calls `gdImage*Ctx()` and the latter fails, we
must not call `gdDPExtractData()`; otherwise a double-free would
happen.  Since `gdImage*Ctx()` are void functions, and we can't change
that for BC reasons, we're introducing static helpers which are used
internally.

We're adding a regression test for `gdImageJpegPtr()`, but not for
`gdImageGifPtr()` and `gdImageWbmpPtr()` since we don't know how to
trigger failure of the respective `gdImage*Ctx()` calls.

This potential security issue has been reported by Solmaz Salimi (aka.
Rooney).

src/gd_gif_out.c

@@ -99,6 +99,7 @@ static void char_init(GifCtx *ctx);
 static void char_out(int c, GifCtx *ctx);
 static void flush_char(GifCtx *ctx);
 
+static int _gdImageGifCtx(gdImagePtr im, gdIOCtxPtr out);
 
 
 
@@ -131,8 +132,11 @@ BGD_DECLARE(void *) gdImageGifPtr(gdImagePtr im, int *size)
 	void *rv;
 	gdIOCtx *out = gdNewDynamicCtx(2048, NULL);
 	if (out == NULL) return NULL;
-	gdImageGifCtx(im, out);
-	rv = gdDPExtractData(out, size);
+	if (!_gdImageGifCtx(im, out)) {
+		rv = gdDPExtractData(out, size);
+	} else {
+		rv = NULL;
+	}
 	out->gd_free(out);
 	return rv;
 }
@@ -220,6 +224,12 @@ BGD_DECLARE(void) gdImageGif(gdImagePtr im, FILE *outFile)
 
 */
 BGD_DECLARE(void) gdImageGifCtx(gdImagePtr im, gdIOCtxPtr out)
+{
+	_gdImageGifCtx(im, out);
+}
+
+/* returns 0 on success, 1 on failure */
+static int _gdImageGifCtx(gdImagePtr im, gdIOCtxPtr out)
 {
 	gdImagePtr pim = 0, tim = im;
 	int interlace, BitsPerPixel;
@@ -231,7 +241,7 @@ BGD_DECLARE(void) gdImageGifCtx(gdImagePtr im, gdIOCtxPtr out)
 		based temporary image. */
 		pim = gdImageCreatePaletteFromTrueColor(im, 1, 256);
 		if(!pim) {
-			return;
+			return 1;
 		}
 		tim = pim;
 	}
@@ -247,6 +257,8 @@ BGD_DECLARE(void) gdImageGifCtx(gdImagePtr im, gdIOCtxPtr out)
 		/* Destroy palette based temporary image. */
 		gdImageDestroy(	pim);
 	}
+
+	return 0;
 }
 
 

src/gd_jpeg.c

@@ -117,6 +117,8 @@ static void fatal_jpeg_error(j_common_ptr cinfo)
 	exit(99);
 }
 
+static int _gdImageJpegCtx(gdImagePtr im, gdIOCtx *outfile, int quality);
+
 /*
  * Write IM to OUTFILE as a JFIF-formatted JPEG image, using quality
  * QUALITY.  If QUALITY is in the range 0-100, increasing values
@@ -231,8 +233,11 @@ BGD_DECLARE(void *) gdImageJpegPtr(gdImagePtr im, int *size, int quality)
 	void *rv;
 	gdIOCtx *out = gdNewDynamicCtx(2048, NULL);
 	if (out == NULL) return NULL;
-	gdImageJpegCtx(im, out, quality);
-	rv = gdDPExtractData(out, size);
+	if (!_gdImageJpegCtx(im, out, quality)) {
+		rv = gdDPExtractData(out, size);
+	} else {
+		rv = NULL;
+	}
 	out->gd_free(out);
 	return rv;
 }
@@ -253,6 +258,12 @@ void jpeg_gdIOCtx_dest(j_compress_ptr cinfo, gdIOCtx *outfile);
 
 */
 BGD_DECLARE(void) gdImageJpegCtx(gdImagePtr im, gdIOCtx *outfile, int quality)
+{
+	_gdImageJpegCtx(im, outfile, quality);
+}
+
+/* returns 0 on success, 1 on failure */
+static int _gdImageJpegCtx(gdImagePtr im, gdIOCtx *outfile, int quality)
 {
 	struct jpeg_compress_struct cinfo;
 	struct jpeg_error_mgr jerr;
@@ -287,7 +298,7 @@ BGD_DECLARE(void) gdImageJpegCtx(gdImagePtr im, gdIOCtx *outfile, int quality)
 		if(row) {
 			gdFree(row);
 		}
-		return;
+		return 1;
 	}
 
 	cinfo.err->emit_message = jpeg_emit_message;
@@ -328,7 +339,7 @@ BGD_DECLARE(void) gdImageJpegCtx(gdImagePtr im, gdIOCtx *outfile, int quality)
 	if(row == 0) {
 		gd_error("gd-jpeg: error: unable to allocate JPEG row structure: gdCalloc returns NULL\n");
 		jpeg_destroy_compress(&cinfo);
-		return;
+		return 1;
 	}
 
 	rowptr[0] = row;
@@ -405,6 +416,7 @@ BGD_DECLARE(void) gdImageJpegCtx(gdImagePtr im, gdIOCtx *outfile, int quality)
 	jpeg_finish_compress(&cinfo);
 	jpeg_destroy_compress(&cinfo);
 	gdFree(row);
+	return 0;
 }
 
 

src/gd_wbmp.c

@@ -88,6 +88,8 @@ int gd_getin(void *in)
 	return (gdGetC((gdIOCtx *)in));
 }
 
+static int _gdImageWBMPCtx(gdImagePtr image, int fg, gdIOCtx *out);
+
 /*
 	Function: gdImageWBMPCtx
 
@@ -100,14 +102,20 @@ int gd_getin(void *in)
 		out   - the stream where to write
 */
 BGD_DECLARE(void) gdImageWBMPCtx(gdImagePtr image, int fg, gdIOCtx *out)
+{
+	_gdImageWBMPCtx(image, fg, out);
+}
+
+/* returns 0 on success, 1 on failure */
+static int _gdImageWBMPCtx(gdImagePtr image, int fg, gdIOCtx *out)
 {
 	int x, y, pos;
 	Wbmp *wbmp;
 
 	/* create the WBMP */
 	if((wbmp = createwbmp(gdImageSX(image), gdImageSY(image), WBMP_WHITE)) == NULL) {
 		gd_error("Could not create WBMP\n");
-		return;
+		return 1;
 	}
 
 	/* fill up the WBMP structure */
@@ -123,11 +131,15 @@ BGD_DECLARE(void) gdImageWBMPCtx(gdImagePtr image, int fg, gdIOCtx *out)
 
 	/* write the WBMP to a gd file descriptor */
 	if(writewbmp(wbmp, &gd_putout, out)) {
+		freewbmp(wbmp);
 		gd_error("Could not save WBMP\n");
+		return 1;
 	}
 
 	/* des submitted this bugfix: gdFree the memory. */
 	freewbmp(wbmp);
+
+	return 0;
 }
 
 /*
@@ -271,8 +283,11 @@ BGD_DECLARE(void *) gdImageWBMPPtr(gdImagePtr im, int *size, int fg)
 	void *rv;
 	gdIOCtx *out = gdNewDynamicCtx(2048, NULL);
 	if (out == NULL) return NULL;
-	gdImageWBMPCtx(im, fg, out);
-	rv = gdDPExtractData(out, size);
+	if (!_gdImageWBMPCtx(im, fg, out)) {
+		rv = gdDPExtractData(out, size);
+	} else {
+		rv = NULL;
+	}
 	out->gd_free(out);
 	return rv;
 }

tests/jpeg/.gitignore

@@ -3,5 +3,6 @@
 /jpeg_empty_file
 /jpeg_im2im
 /jpeg_null
+/jpeg_ptr_double_free
 /jpeg_read
 /jpeg_resolution

tests/jpeg/CMakeLists.txt

@@ -2,6 +2,7 @@ IF(JPEG_FOUND)
 LIST(APPEND TESTS_FILES
 	jpeg_empty_file
 	jpeg_im2im
+	jpeg_ptr_double_free
 	jpeg_null
 )
 

tests/jpeg/Makemodule.am

@@ -2,7 +2,8 @@ if HAVE_LIBJPEG
 libgd_test_programs += \
 	jpeg/jpeg_empty_file \
 	jpeg/jpeg_im2im \
-	jpeg/jpeg_null
+	jpeg/jpeg_null \
+	jpeg/jpeg_ptr_double_free
 
 if HAVE_LIBPNG
 libgd_test_programs += \

tests/jpeg/jpeg_ptr_double_free.c

@@ -0,0 +1,31 @@
+/**
+ * Test that failure to convert to JPEG returns NULL
+ *
+ * We are creating an image, set its width to zero, and pass this image to
+ * `gdImageJpegPtr()` which is supposed to fail, and as such should return NULL.
+ *
+ * See also <https://github.com/libgd/libgd/issues/381>
+ */
+
+
+#include "gd.h"
+#include "gdtest.h"
+
+
+int main()
+{
+    gdImagePtr src, dst;
+    int size;
+
+    src = gdImageCreateTrueColor(1, 10);
+    gdTestAssert(src != NULL);
+
+    src->sx = 0; /* this hack forces gdImageJpegPtr() to fail */
+
+    dst = gdImageJpegPtr(src, &size, 0);
+    gdTestAssert(dst == NULL);
+
+    gdImageDestroy(src);
+
+    return gdNumFailures();
+}