[musl] [PATCH v2] getopt: fix null pointer arithmetic ub

[Alexey Izbyshev <izbyshev@ispras.ru>]

When an option that requires an argument is the last character of
argv[argc-1], getopt computes argv[argc] + optpos. While optpos
is always zero in this case, adding it to null pointer is still
undefined.
---
Changed per https://www.openwall.com/lists/musl/2023/03/10/3.
---
 src/misc/getopt.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/src/misc/getopt.c b/src/misc/getopt.c
index c3f66995..b02b81c3 100644
--- a/src/misc/getopt.c
+++ b/src/misc/getopt.c
@@ -87,7 +87,8 @@ int getopt(int argc, char * const argv[], const char *optstring)
 	if (optstring[i] == ':') {
 		optarg = 0;
 		if (optstring[i+1] != ':' || optpos) {
-			optarg = argv[optind++] + optpos;
+			optarg = argv[optind++];
+			if (optpos) optarg += optpos;
 			optpos = 0;
 		}
 		if (optind > argc) {
-- 
2.39.1