login: Fix updwtmp, updwtmx unlocking

Commit 5a3afa9738 (login: Replace
macro-based control flow with function calls in utmp) introduced
a regression because after it, __libc_updwtmp attempts to unlock
the wrong file descriptor.

(cherry picked from commit 341da5b4b6)

ChangeLog

@@ -1,3 +1,10 @@
+2019-08-15  Florian Weimer  <fweimer@redhat.com>
+
+	* login/utmp_file.c (__libc_updwtmp): Unlock the right file
+	descriptor.
+	* login/Makefile (tests): Add tst-updwtmpx.
+	* login/tst-updwtmpx.c: New file.
+
 2019-08-13  Florian Weimer  <fweimer@redhat.com>
 
 	* login/utmp_file.c (LOCK_FILE, LOCKING_FAILED, UNLOCK_FILE):

login/Makefile

@@ -43,7 +43,7 @@ endif
 subdir-dirs = programs
 vpath %.c programs
 
-tests := tst-utmp tst-utmpx tst-grantpt tst-ptsname tst-getlogin
+tests := tst-utmp tst-utmpx tst-grantpt tst-ptsname tst-getlogin tst-updwtmpx
 
 # Build the -lutil library with these extra functions.
 extra-libs      := libutil

login/tst-updwtmpx.c

@@ -0,0 +1,112 @@
+/* Basic test coverage for updwtmpx.
+   Copyright (C) 2019 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; see the file COPYING.LIB.  If
+   not, see <http://www.gnu.org/licenses/>.  */
+
+/* This program runs a series of tests.  Each one calls updwtmpx
+   twice, to write two records, optionally with misalignment in the
+   file, and reads back the results.  */
+
+#include <errno.h>
+#include <stdlib.h>
+#include <support/check.h>
+#include <support/descriptors.h>
+#include <support/support.h>
+#include <support/temp_file.h>
+#include <support/test-driver.h>
+#include <support/xunistd.h>
+#include <unistd.h>
+#include <utmpx.h>
+
+static int
+do_test (void)
+{
+  /* Two entries filled with an arbitrary bit pattern.  */
+  struct utmpx entries[2];
+  unsigned char pad;
+  {
+    unsigned char *p = (unsigned char *) &entries[0];
+    for (size_t i = 0; i < sizeof (entries); ++i)
+      {
+        p[i] = i;
+      }
+    /* Make sure that the first and second entry and the padding are
+       different.  */
+    p[sizeof (struct utmpx)] = p[0] + 1;
+    pad = p[0] + 2;
+  }
+
+  char *path;
+  int fd = create_temp_file ("tst-updwtmpx-", &path);
+
+  /* Used to check that updwtmpx does not leave an open file
+     descriptor around.  */
+  struct support_descriptors *descriptors = support_descriptors_list ();
+
+  /* updwtmpx is expected to remove misalignment.  Optionally insert
+     one byte of misalignment at the start and in the middle (after
+     the first entry).  */
+  for (int misaligned_start = 0; misaligned_start < 2; ++misaligned_start)
+    for (int misaligned_middle = 0; misaligned_middle < 2; ++misaligned_middle)
+      {
+        if (test_verbose > 0)
+          printf ("info: misaligned_start=%d misaligned_middle=%d\n",
+                  misaligned_start, misaligned_middle);
+
+        xftruncate (fd, 0);
+        TEST_COMPARE (pwrite64 (fd, &pad, misaligned_start, 0),
+                      misaligned_start);
+
+        /* Write first entry and check it.  */
+        errno = 0;
+        updwtmpx (path, &entries[0]);
+        TEST_COMPARE (errno, 0);
+        support_descriptors_check (descriptors);
+        TEST_COMPARE (xlseek (fd, 0, SEEK_END), sizeof (struct utmpx));
+        struct utmpx buffer;
+        TEST_COMPARE (pread64 (fd, &buffer, sizeof (buffer), 0),
+                      sizeof (buffer));
+        TEST_COMPARE_BLOB (&entries[0], sizeof (entries[0]),
+                           &buffer, sizeof (buffer));
+
+        /* Middle mis-alignmet.  */
+        TEST_COMPARE (pwrite64 (fd, &pad, misaligned_middle,
+                                sizeof (struct utmpx)), misaligned_middle);
+
+        /* Write second entry and check both entries.  */
+        errno = 0;
+        updwtmpx (path, &entries[1]);
+        TEST_COMPARE (errno, 0);
+        support_descriptors_check (descriptors);
+        TEST_COMPARE (xlseek (fd, 0, SEEK_END), 2 * sizeof (struct utmpx));
+        TEST_COMPARE (pread64 (fd, &buffer, sizeof (buffer), 0),
+                      sizeof (buffer));
+        TEST_COMPARE_BLOB (&entries[0], sizeof (entries[0]),
+                           &buffer, sizeof (buffer));
+        TEST_COMPARE (pread64 (fd, &buffer, sizeof (buffer), sizeof (buffer)),
+                      sizeof (buffer));
+        TEST_COMPARE_BLOB (&entries[1], sizeof (entries[1]),
+                           &buffer, sizeof (buffer));
+      }
+
+  support_descriptors_free (descriptors);
+  free (path);
+  xclose (fd);
+
+  return 0;
+}
+
+#include <support/test-driver.c>

login/utmp_file.c

@@ -503,7 +503,7 @@ __libc_updwtmp (const char *file, const struct utmp *utmp)
   result = 0;
 
 unlock_return:
-  file_unlock (file_fd);
+  file_unlock (fd);
   file_lock_restore (&fl);
 
   /* Close WTMP file.  */