login/tst-pututxline-lockfail.c

   1 /* Test the lock upgrade path in tst-pututxline.
   2    Copyright (C) 2019-2024 Free Software Foundation, Inc.
   3    This file is part of the GNU C Library.
   4
   5    The GNU C Library is free software; you can redistribute it and/or
   6    modify it under the terms of the GNU Lesser General Public License as
   7    published by the Free Software Foundation; either version 2.1 of the
   8    License, or (at your option) any later version.
   9
  10    The GNU C Library is distributed in the hope that it will be useful,
  11    but WITHOUT ANY WARRANTY; without even the implied warranty of
  12    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  13    Lesser General Public License for more details.
  14
  15    You should have received a copy of the GNU Lesser General Public
  16    License along with the GNU C Library; see the file COPYING.LIB.  If
  17    not, see <https://www.gnu.org/licenses/>.  */
  18
  19 /* pututxline upgrades the read lock on the file to a write lock.
  20    This test verifies that if the lock upgrade fails, the utmp
  21    subsystem remains in a consistent state, so that pututxline can be
  22    called again.  */
  23
  24 #include <errno.h>
  25 #include <fcntl.h>
  26 #include <stdlib.h>
  27 #include <support/check.h>
  28 #include <support/namespace.h>
  29 #include <support/support.h>
  30 #include <support/temp_file.h>
  31 #include <support/xthread.h>
  32 #include <support/xunistd.h>
  33 #include <unistd.h>
  34 #include <utmp.h>
  35 #include <utmpx.h>
  36
  37 /* Path to the temporary utmp file.   */
  38 static char *path;
  39
  40 /* Used to synchronize the subprocesses.  The barrier itself is
  41    allocated in shared memory.  */
  42 static pthread_barrier_t *barrier;
  43
  44 /* Use pututxline to write an entry for PID.  */
  45 static struct utmpx *
  46 write_entry (pid_t pid)
  47 {
  48   struct utmpx ut =
  49     {
  50      .ut_type = LOGIN_PROCESS,
  51      .ut_id = "1",
  52      .ut_user = "root",
  53      .ut_pid = pid,
  54      .ut_line = "entry",
  55      .ut_host = "localhost",
  56     };
  57   return pututxline (&ut);
  58 }
  59
  60 /* Create the initial entry in a subprocess, so that the utmp
  61    subsystem in the original process is not disturbed.  */
  62 static void
  63 subprocess_create_entry (void *closure)
  64 {
  65   TEST_COMPARE (utmpname (path), 0);
  66   TEST_VERIFY (write_entry (101) != NULL);
  67 }
  68
  69 /* Acquire an advisory read lock on PATH.  */
  70 __attribute__ ((noreturn)) static void
  71 subprocess_lock_file (void)
  72 {
  73   int fd = xopen (path, O_RDONLY, 0);
  74
  75   struct flock64 fl =
  76     {
  77      .l_type = F_RDLCK,
  78      fl.l_whence = SEEK_SET,
  79     };
  80   TEST_COMPARE (fcntl64 (fd, F_SETLKW, &fl), 0);
  81
  82   /* Signal to the main process that the lock has been acquired.  */
  83   xpthread_barrier_wait (barrier);
  84
  85   /* Wait for the unlock request from the main process.  */
  86   xpthread_barrier_wait (barrier);
  87
  88   /* Implicitly unlock the file.  */
  89   xclose (fd);
  90
  91   /* Overwrite the existing entry.  */
  92   TEST_COMPARE (utmpname (path), 0);
  93   errno = 0;
  94   setutxent ();
  95   TEST_COMPARE (errno, 0);
  96   TEST_VERIFY (write_entry (102) != NULL);
  97   errno = 0;
  98   endutxent ();
  99   TEST_COMPARE (errno, 0);
 100
 101   _exit (0);
 102 }
 103
 104 static int
 105 do_test (void)
 106 {
 107   xclose (create_temp_file ("tst-pututxline-lockfail-", &path));
 108
 109   {
 110     pthread_barrierattr_t attr;
 111     xpthread_barrierattr_init (&attr);
 112     xpthread_barrierattr_setpshared (&attr, PTHREAD_SCOPE_PROCESS);
 113     barrier = support_shared_allocate (sizeof (*barrier));
 114     xpthread_barrier_init (barrier, &attr, 2);
 115     xpthread_barrierattr_destroy (&attr);
 116   }
 117
 118   /* Write the initial entry.  */
 119   support_isolate_in_subprocess (subprocess_create_entry, NULL);
 120
 121   pid_t locker_pid = xfork ();
 122   if (locker_pid == 0)
 123     subprocess_lock_file ();
 124
 125   /* Wait for the file locking to complete.  */
 126   xpthread_barrier_wait (barrier);
 127
 128   /* Try to add another entry.  This attempt will fail, with EINTR or
 129      EAGAIN.  */
 130   TEST_COMPARE (utmpname (path), 0);
 131   TEST_VERIFY (write_entry (102) == NULL);
 132   if (errno != EINTR)
 133     TEST_COMPARE (errno, EAGAIN);
 134
 135   /* Signal the subprocess to overwrite the entry.  */
 136   xpthread_barrier_wait (barrier);
 137
 138   /* Wait for write and unlock to complete.  */
 139   {
 140     int status;
 141     xwaitpid (locker_pid, &status, 0);
 142     TEST_COMPARE (status, 0);
 143   }
 144
 145   /* The file is no longer locked, so this operation will succeed.  */
 146   TEST_VERIFY (write_entry (103) != NULL);
 147   errno = 0;
 148   endutxent ();
 149   TEST_COMPARE (errno, 0);
 150
 151   /* Check that there is just one entry with the expected contents.
 152      If pututxline becomes desynchronized internally, the entry is not
 153      overwritten (bug 24902).  */
 154   errno = 0;
 155   setutxent ();
 156   TEST_COMPARE (errno, 0);
 157   struct utmpx *ut = getutxent ();
 158   TEST_VERIFY_EXIT (ut != NULL);
 159   TEST_COMPARE (ut->ut_type, LOGIN_PROCESS);
 160   TEST_COMPARE_STRING (ut->ut_id, "1");
 161   TEST_COMPARE_STRING (ut->ut_user, "root");
 162   TEST_COMPARE (ut->ut_pid, 103);
 163   TEST_COMPARE_STRING (ut->ut_line, "entry");
 164   TEST_COMPARE_STRING (ut->ut_host, "localhost");
 165   TEST_VERIFY (getutxent () == NULL);
 166   errno = 0;
 167   endutxent ();
 168   TEST_COMPARE (errno, 0);
 169
 170   xpthread_barrier_destroy (barrier);
 171   support_shared_free (barrier);
 172   free (path);
 173   return 0;
 174 }
 175
 176 #include <support/test-driver.c>