libc/locale: Fix races between localeconv(3) and setlocale(3)

Each locale embeds a lazily initialized lconv which is populated by
localeconv(3) and localeconv_l(3).  When setlocale(3) updates the global
locale, the lconv needs to be (lazily) reinitialized.  To signal this,
we set flag variables in the locale structure.  There are two problems:

- The flags are set before the locale is fully updated, so a concurrent
  localeconv() call can observe partially initialized locale data.
- No barriers ensure that localeconv() observes a fully initialized
  locale if a flag is set.

So, move the flag update appropriately, and use acq/rel barriers to
provide some synchronization.  Note that this is inadequate in the face
of multiple concurrent calls to setlocale(3), but this is not expected
to work regardless.

Thanks to Henry Hu <henry.hu.sh@gmail.com> for providing a test case
demonstrating the race.

PR:		258360
MFC after:	3 weeks
Sponsored by:	The FreeBSD Foundation
Differential Revision:	https://reviews.freebsd.org/D31899

3 files changed, 8 insertions, 8 deletions

diff --git a/lib/libc/locale/lmonetary.c b/lib/libc/locale/lmonetary.c
index 99800ae69922..b8b4e78c060b 100644
--- a/lib/libc/locale/lmonetary.c
+++ b/lib/libc/locale/lmonetary.c
@@ -107,8 +107,6 @@ monetary_load_locale_l(struct xlocale_monetary *loc, int *using_locale,
 		&loc->buffer, "LC_MONETARY",
 		LCMONETARY_SIZE_FULL, LCMONETARY_SIZE_MIN,
 		(const char **)l);
-	if (ret != _LDP_ERROR)
-		*changed = 1;
 	if (ret == _LDP_LOADED) {
 		l->mon_grouping =
 		     __fix_locale_grouping_str(l->mon_grouping);
@@ -146,6 +144,8 @@ monetary_load_locale_l(struct xlocale_monetary *loc, int *using_locale,
 		M_ASSIGN_ICHAR(p_sign_posn);
 		M_ASSIGN_ICHAR(n_sign_posn);
 	}
+	if (ret != _LDP_ERROR)
+		atomic_store_rel_int(changed, 1);
 	return (ret);
 }
 int
diff --git a/lib/libc/locale/lnumeric.c b/lib/libc/locale/lnumeric.c
index 046d1f1817dc..cc1daa3863e3 100644
--- a/lib/libc/locale/lnumeric.c
+++ b/lib/libc/locale/lnumeric.c
@@ -73,8 +73,6 @@ numeric_load_locale(struct xlocale_numeric *loc, int *using_locale, int *changed
 		&loc->buffer, "LC_NUMERIC",
 		LCNUMERIC_SIZE, LCNUMERIC_SIZE,
 		(const char**)l);
-	if (ret != _LDP_ERROR)
-		*changed= 1;
 	if (ret == _LDP_LOADED) {
 		/* Can't be empty according to C99 */
 		if (*l->decimal_point == '\0')
@@ -83,6 +81,8 @@ numeric_load_locale(struct xlocale_numeric *loc, int *using_locale, int *changed
 		l->grouping =
 		    __fix_locale_grouping_str(l->grouping);
 	}
+	if (ret != _LDP_ERROR)
+		atomic_store_rel_int(changed, 1);
 	return (ret);
 }
 
diff --git a/lib/libc/locale/localeconv.c b/lib/libc/locale/localeconv.c
index 641773944e32..130f93c178f4 100644
--- a/lib/libc/locale/localeconv.c
+++ b/lib/libc/locale/localeconv.c
@@ -65,7 +65,7 @@ localeconv_l(locale_t loc)
 	FIX_LOCALE(loc);
     struct lconv *ret = &loc->lconv;
 
-    if (loc->monetary_locale_changed) {
+    if (atomic_load_acq_int(&loc->monetary_locale_changed) != 0) {
 	/* LC_MONETARY part */
         struct lc_monetary_T * mptr; 
 
@@ -94,10 +94,10 @@ localeconv_l(locale_t loc)
 	M_ASSIGN_CHAR(int_n_sep_by_space);
 	M_ASSIGN_CHAR(int_p_sign_posn);
 	M_ASSIGN_CHAR(int_n_sign_posn);
-	loc->monetary_locale_changed = 0;
+	atomic_store_int(&loc->monetary_locale_changed, 0);
     }
 
-    if (loc->numeric_locale_changed) {
+    if (atomic_load_acq_int(&loc->numeric_locale_changed) != 0) {
 	/* LC_NUMERIC part */
         struct lc_numeric_T * nptr; 
 
@@ -107,7 +107,7 @@ localeconv_l(locale_t loc)
 	N_ASSIGN_STR(decimal_point);
 	N_ASSIGN_STR(thousands_sep);
 	N_ASSIGN_STR(grouping);
-	loc->numeric_locale_changed = 0;
+	atomic_store_int(&loc->numeric_locale_changed, 0);
     }
 
     return ret;