tzcode: Don't treat TZDEFAULT as tainted

tzset() calls zoneinit() with the FROMENV flag set unconditionally, so
if TZ is unset and we use TZDEFAULT instead, we were still treating it
as if it came from the environment.  Unset the FROMENV flag if name is
null and we switch to TZDEFAULT, or if, after skipping the optional
leading colon, we find that name is identical to TZDEFAULT.

This incorporates upstream change d0e0b00f846c ("Avoid unnecessary
access, stat calls").

Fixes:		b6ea2513f776 ("tzcode: Limit TZ for setugid programs")
Event:		Oslo Hackathon 202508
Reviewed by:	philip
Differential Revision:	https://reviews.freebsd.org/D52240

1 files changed, 6 insertions, 4 deletions

diff --git a/contrib/tzcode/localtime.c b/contrib/tzcode/localtime.c
index a80d422f2955..15afeeecb6d0 100644
--- a/contrib/tzcode/localtime.c
+++ b/contrib/tzcode/localtime.c
@@ -615,6 +615,7 @@ tzloadbody(char const *name, struct state *sp, char tzloadflags,
 		name = TZDEFAULT;
 		if (! name)
 		  return EINVAL;
+		tzloadflags &= ~TZLOAD_FROMENV;
 	}
 
 	if (name[0] == ':')
@@ -670,11 +671,13 @@ tzloadbody(char const *name, struct state *sp, char tzloadflags,
 	fid = _open(name, (O_RDONLY | O_BINARY | O_CLOEXEC | O_CLOFORK
 			  | O_IGNORE_CTTY | O_NOCTTY));
 #else /* __FreeBSD__ */
+	if ((tzloadflags & TZLOAD_FROMENV) && strcmp(name, TZDEFAULT) == 0)
+          tzloadflags &= ~TZLOAD_FROMENV;
 	relname = name;
 	if (strncmp(relname, TZDIR "/", strlen(TZDIR) + 1) == 0)
 	  relname += strlen(TZDIR) + 1;
 	dd = _open(TZDIR, O_DIRECTORY | O_RDONLY);
-	if (issetugid() && (tzloadflags & TZLOAD_FROMENV)) {
+	if ((tzloadflags & TZLOAD_FROMENV) && issetugid()) {
 	  if (dd < 0)
 	    return errno;
 	  if (fstatat(dd, name, &sb, AT_RESOLVE_BENEATH) < 0) {
@@ -1624,14 +1627,13 @@ zoneinit(struct state *sp, char const *name, char tzloadflags)
 static void
 tzset_unlocked(void)
 {
+  char const *name = getenv("TZ");
 #ifdef __FreeBSD__
-  tzset_unlocked_name(getenv("TZ"));
+  tzset_unlocked_name(name);
 }
 static void
 tzset_unlocked_name(char const *name)
 {
-#else
-  char const *name = getenv("TZ");
 #endif
   struct state *sp = lclptr;
   int lcl = name ? strlen(name) < sizeof lcl_TZname : -1;