Fix #77269: Potential unsigned underflow in gdImageScale

Belatedly, we're porting the respective upstream patch[1].

[1] <libgd/libgd@60bfb40>

Author: cmb69

ext/gd/libgd/gd_interpolation.c

@@ -890,8 +890,13 @@ static inline LineContribType * _gdContributionsAlloc(unsigned int line_length,
 {
 	unsigned int u = 0;
 	LineContribType *res;
-	int overflow_error = 0;
+	size_t weights_size;
 
+	if (overflow2(windows_size, sizeof(double))) {
+		return NULL;
+	} else {
+		weights_size = windows_size * sizeof(double);
+	}
 	res = (LineContribType *) gdMalloc(sizeof(LineContribType));
 	if (!res) {
 		return NULL;
@@ -908,15 +913,10 @@ static inline LineContribType * _gdContributionsAlloc(unsigned int line_length,
 		return NULL;
 	}
 	for (u = 0 ; u < line_length ; u++) {
-		if (overflow2(windows_size, sizeof(double))) {
-			overflow_error = 1;
-		} else {
-			res->ContribRow[u].Weights = (double *) gdMalloc(windows_size * sizeof(double));
-		}
-		if (overflow_error == 1 || res->ContribRow[u].Weights == NULL) {
+		res->ContribRow[u].Weights = (double *) gdMalloc(weights_size);
+		if (res->ContribRow[u].Weights == NULL) {
 			unsigned int i;
-			u--;
-			for (i=0;i<=u;i++) {
+			for (i=0;i<u;i++) {
 				gdFree(res->ContribRow[i].Weights);
 			}
 			gdFree(res->ContribRow);

ext/gd/tests/bug77269.phpt

@@ -0,0 +1,21 @@
+--TEST--
+Bug #77269 (Potential unsigned underflow in gdImageScale)
+--SKIPIF--
+<?php
+if (!extension_loaded('gd')) die('skip gd extension not available');
+if (getenv("SKIP_SLOW_TESTS")) die("skip slow test");
+?>
+--INI--
+memory_limit=2G
+--FILE--
+<?php
+$im = imagecreate(2**28, 1);
+if(is_resource($im)) {
+	imagescale($im, 1, 1, IMG_TRIANGLE);
+}
+?>
+===DONE===
+--EXPECTF--
+Warning: imagecreate():%S product of memory allocation multiplication would exceed INT_MAX, failing operation gracefully
+ in %s on line %d
+===DONE===