--- php5.orig/ext/ereg/regex/regcomp.c
+++ php5/ext/ereg/regex/regcomp.c
@@ -95,6 +95,7 @@ int cflags;
 	register struct parse *p = &pa;
 	register int i;
 	register size_t len;
+	size_t maxlen;
 #ifdef REDEBUG
 #	define	GOODFLAGS(f)	(f)
 #else
@@ -117,7 +118,22 @@ int cflags;
 							(NC-1)*sizeof(cat_t));
 	if (g == NULL)
 		return(REG_ESPACE);
-	p->ssize = len/(size_t)2*(size_t)3 + (size_t)1;	/* ugh */
+	/*
+	 * Limit the pattern space to avoid a 32-bit overflow on buffer
+	 * extension.  Also avoid any signed overflow in case of conversion
+	 * so make the real limit based on a 31-bit overflow.
+	 *
+	 * Likely not applicable on 64-bit systems but handle the case
+	 * generically (who are we to stop people from using ~715MB+
+	 * patterns?).
+	 */
+	maxlen = ((size_t)-1 >> 1) / sizeof(sop) * 2 / 3;
+	if (len >= maxlen) {
+		free((char *)g);
+		return(REG_ESPACE);
+	}
+	p->ssize = len/(size_t)2*(size_t)3 + (size_t)1; /* ugh */
+	assert(p->ssize >= len);
 	p->strip = (sop *)malloc(p->ssize * sizeof(sop));
 	p->slen = 0;
 	if (p->strip == NULL) {