[glibc] duplocale: protect use of global locale (bug 23970)

[Andreas Schwab <schwab@sourceware.org>]

https://sourceware.org/git/gitweb.cgi?p=glibc.git;h=513331b788a3fa633f1d0417d43915e16a0c88f0

commit 513331b788a3fa633f1d0417d43915e16a0c88f0
Author: Andreas Schwab <schwab@suse.de>
Date:   Wed Mar 6 12:59:47 2024 +0100

    duplocale: protect use of global locale (bug 23970)
    
    Protect the global locale from being modified while we compute the size of
    the locale category names.  That allows the use of the global locale in a
    single thread, while all other threads use the thread safe locale
    functions.

Diff:
---
 locale/duplocale.c | 14 ++++++++------
 1 file changed, 8 insertions(+), 6 deletions(-)

diff --git a/locale/duplocale.c b/locale/duplocale.c
index a755ac5c36..bad476700f 100644
--- a/locale/duplocale.c
+++ b/locale/duplocale.c
@@ -43,6 +43,11 @@ __duplocale (locale_t dataset)
   int cnt;
   size_t names_len = 0;
 
+  /* If dataset points to _nl_global_locale, we need to prevent other
+     threads from modifying it.  We also modify global data below (the
+     usage counts).  */
+  __libc_rwlock_wrlock (__libc_setlocale_lock);
+
   /* Calculate the total space we need to store all the names.  */
   for (cnt = 0; cnt < __LC_LAST; ++cnt)
     if (cnt != LC_ALL && dataset->__names[cnt] != _nl_C_name)
@@ -55,9 +60,6 @@ __duplocale (locale_t dataset)
     {
       char *namep = (char *) (result + 1);
 
-      /* We modify global data (the usage counts).  */
-      __libc_rwlock_wrlock (__libc_setlocale_lock);
-
       for (cnt = 0; cnt < __LC_LAST; ++cnt)
 	if (cnt != LC_ALL)
 	  {
@@ -78,11 +80,11 @@ __duplocale (locale_t dataset)
       result->__ctype_b = dataset->__ctype_b;
       result->__ctype_tolower = dataset->__ctype_tolower;
       result->__ctype_toupper = dataset->__ctype_toupper;
-
-      /* It's done.  */
-      __libc_rwlock_unlock (__libc_setlocale_lock);
     }
 
+  /* It's done.  */
+  __libc_rwlock_unlock (__libc_setlocale_lock);
+
   return result;
 }
 weak_alias (__duplocale, duplocale)