kbuild: scripts/basic/fixdep segfault on pathological string-o-death

build scripts: fixdep blows segfault on string CONFIG_MODULE seen

The string "CONFIG_MODULE" appearing anywhere in a source file causes
fixdep to segfault.  This string appeared in the wild in the current
mISDN sources (I think they meant CONFIG_MODULES).  But it shouldn't
segfault (esp as CONFIG_MODULE appeared in a quoted string).
Signed-off-by: NAndy Green <andy@warmcat.com>
Signed-off-by: NSam Ravnborg <sam@ravnborg.org>

scripts/basic/fixdep.c

@@ -249,6 +249,8 @@ void parse_config_file(char *map, size_t len)
 	found:
 		if (!memcmp(q - 7, "_MODULE", 7))
 			q -= 7;
+		if( (q-p-7) < 0 )
+			continue;
 		use_config(p+7, q-p-7);
 	}
 }