Fix handling of unterminated bracket expressions in fnmatch (bug 28792)

When fnmatch processes a bracket expression, and eventually finds it to be
unterminated, it should rescan it, treating the starting bracket as a
normal character.  That didn't happen when a matching character was found
while scanning the bracket expression.

posix/Makefile

@@ -101,7 +101,7 @@ tests		:= test-errno tstgetopt testfnm runtests runptests \
 		   bug-getopt5 tst-getopt_long1 bug-regex34 bug-regex35 \
 		   tst-pathconf tst-rxspencer-no-utf8 \
 		   tst-fnmatch3 bug-regex36 \
-		   tst-fnmatch4 tst-fnmatch5 tst-fnmatch6 \
+		   tst-fnmatch4 tst-fnmatch5 tst-fnmatch6 tst-fnmatch7 \
 		   tst-posix_spawn-fd tst-posix_spawn-setsid \
 		   tst-posix_fadvise tst-posix_fadvise64 \
 		   tst-sysconf-empty-chroot tst-glob_symlinks tst-fexecve \

posix/fnmatch_loop.c

@@ -823,8 +823,13 @@ FCT (const CHAR *pattern, const CHAR *string, const CHAR *string_end,
             while ((c = *p++) != L_(']'))
               {
                 if (c == L_('\0'))
-                  /* [... (unterminated) loses.  */
-                  return FNM_NOMATCH;
+		  {
+		    /* [ unterminated, treat as normal character.  */
+		    p = p_init;
+		    n = n_init;
+		    c = L_('[');
+		    goto normal_match;
+		  }
 
                 if (!(flags & FNM_NOESCAPE) && c == L_('\\'))
                   {

posix/tst-fnmatch7.c

@@ -0,0 +1,37 @@
+/* Test for fnmatch handling of unterminated bracket expression (bug 28792)
+   Copyright (C) 2022 Free Software Foundation, Inc.
+   This file is part of the GNU C Library.
+
+   The GNU C Library is free software; you can redistribute it and/or
+   modify it under the terms of the GNU Lesser General Public
+   License as published by the Free Software Foundation; either
+   version 2.1 of the License, or (at your option) any later version.
+
+   The GNU C Library is distributed in the hope that it will be useful,
+   but WITHOUT ANY WARRANTY; without even the implied warranty of
+   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+   Lesser General Public License for more details.
+
+   You should have received a copy of the GNU Lesser General Public
+   License along with the GNU C Library; if not, see
+   <https://www.gnu.org/licenses/>.  */
+
+#include <fnmatch.h>
+#include <support/check.h>
+
+static int
+do_test (void)
+{
+  /* An unterminated bracket expression should be rescanned, treating the
+     open bracket as a normal character.  The backslash causes the close
+     bracket to be treated as a normal character, not ending the bracket
+     expression.  */
+  TEST_VERIFY (fnmatch ("[", "[", 0) == 0);
+  TEST_VERIFY (fnmatch ("[[", "[[", 0) == 0);
+  TEST_VERIFY (fnmatch ("[\\]", "[]", 0) == 0);
+  TEST_VERIFY (fnmatch ("[[\\]", "[[]", 0) == 0);
+
+  return 0;
+}
+
+#include <support/test-driver.c>