The 0x (or 0X) prefix in base 16 is optional so only skip over the

prefix if the character following it is a valid hex char.  The C99
standard is clear that given the string "0xy" zero should be returned
and endptr set to point to the "x".  OK deraadt@ espie@

src/lib/libc/stdlib/strtoimax.c

@@ -1,4 +1,4 @@
-/*	$OpenBSD: strtoimax.c,v 1.3 2015/09/12 16:23:14 guenther Exp $	*/
+/*	$OpenBSD: strtoimax.c,v 1.4 2017/07/06 16:23:11 millert Exp $	*/
 /*
  * Copyright (c) 1992 The Regents of the University of California.
  * All rights reserved.
@@ -74,8 +74,8 @@ strtoimax(const char *nptr, char **endptr, int base)
 		if (c == '+')
 			c = *s++;
 	}
-	if ((base == 0 || base == 16) &&
-	    c == '0' && (*s == 'x' || *s == 'X')) {
+	if ((base == 0 || base == 16) && c == '0' &&
+	    (*s == 'x' || *s == 'X') && isxdigit((unsigned char)s[1])) {
 		c = s[1];
 		s += 2;
 		base = 16;

src/lib/libc/stdlib/strtol.c

@@ -1,4 +1,4 @@
-/*	$OpenBSD: strtol.c,v 1.11 2015/09/13 08:31:48 guenther Exp $ */
+/*	$OpenBSD: strtol.c,v 1.12 2017/07/06 16:23:11 millert Exp $ */
 /*
  * Copyright (c) 1990 The Regents of the University of California.
  * All rights reserved.
@@ -75,8 +75,8 @@ strtol(const char *nptr, char **endptr, int base)
 		if (c == '+')
 			c = *s++;
 	}
-	if ((base == 0 || base == 16) &&
-	    c == '0' && (*s == 'x' || *s == 'X')) {
+	if ((base == 0 || base == 16) && c == '0' &&
+	    (*s == 'x' || *s == 'X') && isxdigit((unsigned char)s[1])) {
 		c = s[1];
 		s += 2;
 		base = 16;

src/lib/libc/stdlib/strtoll.c

@@ -1,4 +1,4 @@
-/*	$OpenBSD: strtoll.c,v 1.9 2015/09/13 08:31:48 guenther Exp $ */
+/*	$OpenBSD: strtoll.c,v 1.10 2017/07/06 16:23:11 millert Exp $ */
 /*
  * Copyright (c) 1992 The Regents of the University of California.
  * All rights reserved.
@@ -77,8 +77,8 @@ strtoll(const char *nptr, char **endptr, int base)
 		if (c == '+')
 			c = *s++;
 	}
-	if ((base == 0 || base == 16) &&
-	    c == '0' && (*s == 'x' || *s == 'X')) {
+	if ((base == 0 || base == 16) && c == '0' &&
+	    (*s == 'x' || *s == 'X') && isxdigit((unsigned char)s[1])) {
 		c = s[1];
 		s += 2;
 		base = 16;

src/lib/libc/stdlib/strtoul.c

@@ -1,4 +1,4 @@
-/*	$OpenBSD: strtoul.c,v 1.10 2015/09/13 08:31:48 guenther Exp $ */
+/*	$OpenBSD: strtoul.c,v 1.11 2017/07/06 16:23:11 millert Exp $ */
 /*
  * Copyright (c) 1990 The Regents of the University of California.
  * All rights reserved.
@@ -69,8 +69,8 @@ strtoul(const char *nptr, char **endptr, int base)
 		if (c == '+')
 			c = *s++;
 	}
-	if ((base == 0 || base == 16) &&
-	    c == '0' && (*s == 'x' || *s == 'X')) {
+	if ((base == 0 || base == 16) && c == '0' &&
+	    (*s == 'x' || *s == 'X') && isxdigit((unsigned char)s[1])) {
 		c = s[1];
 		s += 2;
 		base = 16;

src/lib/libc/stdlib/strtoull.c

@@ -1,4 +1,4 @@
-/*	$OpenBSD: strtoull.c,v 1.8 2015/09/13 08:31:48 guenther Exp $ */
+/*	$OpenBSD: strtoull.c,v 1.9 2017/07/06 16:23:11 millert Exp $ */
 /*
  * Copyright (c) 1992 The Regents of the University of California.
  * All rights reserved.
@@ -71,8 +71,8 @@ strtoull(const char *nptr, char **endptr, int base)
 		if (c == '+')
 			c = *s++;
 	}
-	if ((base == 0 || base == 16) &&
-	    c == '0' && (*s == 'x' || *s == 'X')) {
+	if ((base == 0 || base == 16) && c == '0' &&
+	    (*s == 'x' || *s == 'X') && isxdigit((unsigned char)s[1])) {
 		c = s[1];
 		s += 2;
 		base = 16;

src/lib/libc/stdlib/strtoumax.c

@@ -1,4 +1,4 @@
-/*	$OpenBSD: strtoumax.c,v 1.3 2015/09/12 16:23:14 guenther Exp $	*/
+/*	$OpenBSD: strtoumax.c,v 1.4 2017/07/06 16:23:11 millert Exp $	*/
 /*
  * Copyright (c) 1992 The Regents of the University of California.
  * All rights reserved.
@@ -68,8 +68,8 @@ strtoumax(const char *nptr, char **endptr, int base)
 		if (c == '+')
 			c = *s++;
 	}
-	if ((base == 0 || base == 16) &&
-	    c == '0' && (*s == 'x' || *s == 'X')) {
+	if ((base == 0 || base == 16) && c == '0' &&
+	    (*s == 'x' || *s == 'X') && isxdigit((unsigned char)s[1])) {
 		c = s[1];
 		s += 2;
 		base = 16;