[src/trunk]: src/usr.bin/make make(1): fix undefined behavior in Parse_IsVar

[rillig <rillig%NetBSD.org@localhost>]

details:   https://anonhg.NetBSD.org/src/rev/049ceccf97f0
branches:  trunk
changeset: 945648:049ceccf97f0
user:      rillig <rillig%NetBSD.org@localhost>
date:      Mon Nov 02 22:50:55 2020 +0000

description:
make(1): fix undefined behavior in Parse_IsVar

Even though the pointer was out-of-bounds, a crash was unlikely in
practice, since typical C compilers don't check the pointers for invalid
values after each modification.  The memory it pointed to was not
accessed though.

diffstat:

 usr.bin/make/parse.c |  10 ++++------
 1 files changed, 4 insertions(+), 6 deletions(-)

diffs (38 lines):

diff -r 45d1dbccdd9a -r 049ceccf97f0 usr.bin/make/parse.c
--- a/usr.bin/make/parse.c      Mon Nov 02 22:46:52 2020 +0000
+++ b/usr.bin/make/parse.c      Mon Nov 02 22:50:55 2020 +0000
@@ -1,4 +1,4 @@
-/*     $NetBSD: parse.c,v 1.421 2020/11/02 22:44:29 rillig Exp $       */
+/*     $NetBSD: parse.c,v 1.422 2020/11/02 22:50:55 rillig Exp $       */
 
 /*
  * Copyright (c) 1988, 1989, 1990, 1993
@@ -117,7 +117,7 @@
 #include "pathnames.h"
 
 /*     "@(#)parse.c    8.3 (Berkeley) 3/19/94" */
-MAKE_RCSID("$NetBSD: parse.c,v 1.421 2020/11/02 22:44:29 rillig Exp $");
+MAKE_RCSID("$NetBSD: parse.c,v 1.422 2020/11/02 22:50:55 rillig Exp $");
 
 /* types and constants */
 
@@ -1832,7 +1832,6 @@
 {
     VarAssignParsed pvar;
     const char *firstSpace = NULL;
-    char ch;
     int level = 0;
 
     /* Skip to variable name */
@@ -1850,9 +1849,8 @@
 #endif
 
     /* Scan for one of the assignment operators outside a variable expansion */
-    /* FIXME: undefined behavior. In unit-tests/varname.mk:try1, at the end
-     * of the loop, p already points to the next line. */
-    while ((ch = *p++) != 0) {
+    while (*p != '\0') {
+        char ch = *p++;
        if (ch == '(' || ch == '{') {
            level++;
            continue;