1 files changed, 193 insertions, 0 deletions
diff --git a/login/tst-pututxline-cache.c b/login/tst-pututxline-cache.c
new file mode 100644
index 0000000000..3f30dd1776
--- /dev/null
+++ b/login/tst-pututxline-cache.c
@@ -0,0 +1,193 @@
+/* Test case for cache invalidation after concurrent write (bug 24882).
+   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 test writes an entry to the utmpx file, reads it (so that it
+   is cached) in process1, and overwrites the same entry in process2
+   with something that does not match the search criteria.  At this
+   point, the cache of the first process is stale, and when process1
+   attempts to write a new record which would have gone to the same
+   place (as indicated by the cache), it needs to realize that it has
+   to pick a different slot because the old slot is now used for
+   something else.  */
+
+#include <errno.h>
+#include <stdlib.h>
+#include <string.h>
+#include <support/check.h>
+#include <support/namespace.h>
+#include <support/support.h>
+#include <support/temp_file.h>
+#include <support/xthread.h>
+#include <support/xunistd.h>
+#include <utmp.h>
+#include <utmpx.h>
+
+/* Set to the path of the utmp file.  */
+static char *utmp_file;
+
+/* Used to synchronize the subprocesses.  The barrier itself is
+   allocated in shared memory.  */
+static pthread_barrier_t *barrier;
+
+/* setutxent with error checking.  */
+static void
+xsetutxent (void)
+{
+  errno = 0;
+  setutxent ();
+  TEST_COMPARE (errno, 0);
+}
+
+/* getutxent with error checking.  */
+static struct utmpx *
+xgetutxent (void)
+{
+  errno = 0;
+  struct utmpx *result = getutxent ();
+  if (result == NULL)
+    FAIL_EXIT1 ("getutxent: %m");
+  return result;
+}
+
+static void
+put_entry (const char *id, pid_t pid, const char *user, const char *line)
+{
+  struct utmpx ut =
+    {
+     .ut_type = LOGIN_PROCESS,
+     .ut_pid = pid,
+     .ut_host = "localhost",
+    };
+  strcpy (ut.ut_id, id);
+  strncpy (ut.ut_user, user, sizeof (ut.ut_user));
+  strncpy (ut.ut_line, line, sizeof (ut.ut_line));
+  TEST_VERIFY (pututxline (&ut) != NULL);
+}
+
+/* Use two cooperating subprocesses to avoid issues related to
+   unlock-on-close semantics of POSIX advisory locks.  */
+
+static __attribute__ ((noreturn)) void
+process1 (void)
+{
+  TEST_COMPARE (utmpname (utmp_file), 0);
+
+  /* Create an entry.  */
+  xsetutxent ();
+  put_entry ("1", 101, "root", "process1");
+
+  /* Retrieve the entry.  This will fill the internal cache.  */
+  {
+    errno = 0;
+    setutxent ();
+    TEST_COMPARE (errno, 0);
+    struct utmpx ut =
+      {
+       .ut_type = LOGIN_PROCESS,
+       .ut_line = "process1",
+      };
+    struct utmpx *result = getutxline (&ut);
+    if (result == NULL)
+      FAIL_EXIT1 ("getutxline (\"process1\"): %m");
+    TEST_COMPARE (result->ut_pid, 101);
+  }
+
+  /* Signal the other process to overwrite the entry.  */
+  xpthread_barrier_wait (barrier);
+
+  /* Wait for the other process to complete the write operation.  */
+  xpthread_barrier_wait (barrier);
+
+  /* Add another entry.  Note: This time, there is no setutxent call.  */
+  put_entry ("1", 103, "root", "process1");
+
+  _exit (0);
+}
+
+static void
+process2 (void *closure)
+{
+  /* Wait for the first process to write its entry.  */
+  xpthread_barrier_wait (barrier);
+
+  /* Truncate the file.  The glibc interface does not support
+     re-purposing records, but an external expiration mechanism may
+     trigger this.  */
+  TEST_COMPARE (truncate64 (utmp_file, 0), 0);
+
+  /* Write the replacement entry.  */
+  TEST_COMPARE (utmpname (utmp_file), 0);
+  xsetutxent ();
+  put_entry ("2", 102, "user", "process2");
+
+  /* Signal the other process that the entry has been replaced.  */
+  xpthread_barrier_wait (barrier);
+}
+
+static int
+do_test (void)
+{
+  xclose (create_temp_file ("tst-tumpx-cache-write-", &utmp_file));
+  {
+    pthread_barrierattr_t attr;
+    xpthread_barrierattr_init (&attr);
+    xpthread_barrierattr_setpshared (&attr, PTHREAD_SCOPE_PROCESS);
+    barrier = support_shared_allocate (sizeof (*barrier));
+    xpthread_barrier_init (barrier, &attr, 2);
+  }
+
+  /* Run both subprocesses in parallel.  */
+  {
+    pid_t pid1 = xfork ();
+    if (pid1 == 0)
+      process1 ();
+    support_isolate_in_subprocess (process2, NULL);
+    int status;
+    xwaitpid (pid1, &status, 0);
+    TEST_COMPARE (status, 0);
+  }
+
+  /* Check that the utmpx database contains the expected records.  */
+  {
+    TEST_COMPARE (utmpname (utmp_file), 0);
+    xsetutxent ();
+
+    struct utmpx *ut = xgetutxent ();
+    TEST_COMPARE_STRING (ut->ut_id, "2");
+    TEST_COMPARE (ut->ut_pid, 102);
+    TEST_COMPARE_STRING (ut->ut_user, "user");
+    TEST_COMPARE_STRING (ut->ut_line, "process2");
+
+    ut = xgetutxent ();
+    TEST_COMPARE_STRING (ut->ut_id, "1");
+    TEST_COMPARE (ut->ut_pid, 103);
+    TEST_COMPARE_STRING (ut->ut_user, "root");
+    TEST_COMPARE_STRING (ut->ut_line, "process1");
+
+    if (getutxent () != NULL)
+      FAIL_EXIT1 ("additional utmpx entry");
+  }
+
+  xpthread_barrier_destroy (barrier);
+  support_shared_free (barrier);
+  free (utmp_file);
+
+  return 0;
+}
+
+#include <support/test-driver.c>