handle password file locking.

3 files changed, 194 insertions, 3 deletions

diff --git a/shadow/Makefile b/shadow/Makefile
index 943881f1f1..614f7afdd4 100644
--- a/shadow/Makefile
+++ b/shadow/Makefile
@@ -23,7 +23,8 @@ subdir	:= shadow
 
 headers		= shadow.h
 routines	= getspent getspnam sgetspent fgetspent putspent \
-		  getspent_r getspnam_r sgetspent_r fgetspent_r
+		  getspent_r getspnam_r sgetspent_r fgetspent_r \
+		  lckpwdf
 
 
 include ../Rules
diff --git a/shadow/lckpwdf.c b/shadow/lckpwdf.c
new file mode 100644
index 0000000000..fb1c4b2e5e
--- /dev/null
+++ b/shadow/lckpwdf.c
@@ -0,0 +1,181 @@
+/* lckpwdf - handle locking of password file.
+Copyright (C) 1996 Free Software Foundation, Inc.
+This file is part of the GNU C Library.
+Contributed by Ulrich Drepper <drepper@cygnus.com>, 1996.
+
+The GNU C Library is free software; you can redistribute it and/or
+modify it under the terms of the GNU Library General Public License as
+published by the Free Software Foundation; either version 2 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
+Library General Public License for more details.
+
+You should have received a copy of the GNU Library General Public
+License along with the GNU C Library; see the file COPYING.LIB.  If
+not, write to the Free Software Foundation, Inc., 59 Temple Place - Suite 330,
+Boston, MA 02111-1307, USA.  */
+
+#include <fcntl.h>
+#include <libc-lock.h>
+#include <shadow.h>
+#include <signal.h>
+#include <string.h>
+#include <unistd.h>
+#include <sys/file.h>
+
+
+/* Name of the lock file.  */
+#define PWD_LOCKFILE "/var/lock/lock.pwd"
+
+/* How long to wait for getting the lock before returning with an
+   error.  */
+#define TIMEOUT 15 /* sec */
+
+
+/* File descriptor for lock file.  */
+static int lock_fd = -1;
+
+/* Prevent problems in multithreaded program by using mutex.  */
+__libc_lock_define_initialized (static, lock)
+
+
+/* Prototypes for local functions.  */
+static void noop_handler __P ((int __sig));
+
+
+/* We cannot simply return in error cases.  We have to close the file
+   and perhaps restore the signal handler.  */
+#define RETURN_CLOSE_FD(code)						      \
+  do {									      \
+    if ((code) < 0 && lock_fd >= 0)					      \
+      {									      \
+	close (lock_fd);						      \
+	lock_fd = -1;							      \
+      }									      \
+    __libc_lock_unlock (lock);						      \
+    return (code);							      \
+  } while (0)
+
+#define RETURN_RESTORE_HANDLER(code)					      \
+  do {									      \
+    /* Restore old action handler for alarm.  We don't need to know	      \
+       about the current one.  */					      \
+    sigaction (SIGALRM, &saved_act, NULL);				      \
+    RETURN_CLOSE_FD (code);						      \
+  } while (0)
+
+#define RETURN_CLEAR_ALARM(code)					      \
+  do {									      \
+    /* Clear alarm.  */							      \
+    alarm (0);								      \
+    /* Restore old set of handled signals.  We don't need to know	      \
+       about the current one.*/						      \
+    sigprocmask (SIG_SETMASK, &saved_set, NULL);			      \
+    RETURN_RESTORE_HANDLER (code);					      \
+  } while (0)
+
+
+int
+__lckpwdf ()
+{
+  int flags;
+  sigset_t saved_set;			/* Saved set of caught signals.  */
+  struct sigaction saved_act;		/* Saved signal action.  */
+  sigset_t new_set;			/* New set of caught signals.  */
+  struct sigaction new_act;		/* New signal action.  */
+  int result;
+
+  if (lock_fd != -1)
+    /* Still locked by own process.  */
+    return -1;
+
+  /* Prevent problems caused by multiple threads.  */
+  __libc_lock_lock (lock);
+
+  lock_fd = open (PWD_LOCKFILE, O_WRONLY | O_CREAT, 0600);
+  if (lock_fd == -1)
+    /* Cannot create lock file.  */
+    RETURN_CLOSE_FD (-1);
+
+  /* Make sure file gets correctly closed when process finished.  */
+  flags = fcntl (lock_fd, F_GETFD, 0);
+  if (flags == -1)
+    /* Cannot get file flags.  */
+    RETURN_CLOSE_FD (-1);
+  flags |= FD_CLOEXEC;		/* Close on exit.  */
+  if (fcntl (lock_fd, F_SETFD, flags) < 0)
+    /* Cannot set new flags.  */
+    RETURN_CLOSE_FD (-1);
+
+  /* Now we have to get exclusive write access.  Since multiple
+     process could try this we won't stop when it first fails.
+     Instead we set a timeout for the system call.  Once the timer
+     expires it is likely that there are some problems which cannot be
+     resolved by waiting.
+
+     It is important that we don't change the signal state.  We must
+     restore the old signal behaviour.  */
+  memset (&new_act, '\0', sizeof (struct sigaction));
+  new_act.sa_handler = noop_handler;
+  sigfillset (&new_act.sa_mask);
+  new_act.sa_flags = 0ul;
+
+  /* Install new action handler for alarm and save old.  */
+  if (sigaction (SIGALRM, &new_act, &saved_act) < 0)
+    /* Cannot install signal handler.  */
+    RETURN_CLOSE_FD (-1);
+
+  /* Now make sure the alarm signal is not blocked.  */
+  sigemptyset (&new_set);
+  sigaddset (&new_set, SIGALRM);
+  if (sigprocmask (SIG_UNBLOCK, &new_set, &saved_set) < 0)
+    RETURN_RESTORE_HANDLER (-1);
+
+  /* Start timer.  If we cannot get the lock in the specified time we
+     get a signal.  */
+  alarm (TIMEOUT);
+
+  /* Try to get the lock.  */
+  result = flock (lock_fd, LOCK_EX);
+
+  RETURN_CLEAR_ALARM (result);
+}
+weak_alias (__lckpwdf, lckpwdf)
+
+
+int
+__ulckpwdf ()
+{
+  int result;
+
+  if (lock_fd == -1)
+    /* There is no lock set.  */
+    result = -1;
+  else
+    {
+      /* Prevent problems caused by multiple threads.  */
+      __libc_lock_lock (&lock);
+
+      result = close (lock_fd);
+
+      /* Mark descriptor as unused.  */
+      lock_fd = -1;
+
+      /* Clear mutex.  */
+      __libc_lock_unlock (lock);
+    }
+
+  return result;
+}
+weak_alias (__ulckpwdf, ulckpwdf)
+
+
+static void
+noop_handler (sig)
+     int sig;
+{
+  /* We simply return which makes the `flock' call return with an error.  */
+}
diff --git a/shadow/shadow.h b/shadow/shadow.h
index 88199a9856..b1a4c82b4e 100644
--- a/shadow/shadow.h
+++ b/shadow/shadow.h
@@ -46,8 +46,8 @@ struct spwd
 				   the password.  */
   __time_t sp_inact;		/* Number of days the account may be
 				   inactive.  */
-  __time_t sp_expire;		/* Number of days since 700101 until account
-				   expires.  */
+  __time_t sp_expire;		/* Number of days since 1970-01-01 until
+				   account expires.  */
   unsigned long int sp_flag;	/* Reserved.  */
 };
 
@@ -103,6 +103,15 @@ extern struct spwd *fgetspent_r __P ((FILE *__stream,
 				      char *__buffer, int __buflen));
 #endif	/* reentrant */
 
+
+/* Protect password file against multi writers.  */
+extern int __lckpwdf __P ((void));
+extern int lckpwdf __P ((void));
+
+/* Unlock password file.  */
+extern int __ulckpwdf __P ((void));
+extern int ulckpwdf __P ((void));
+
 __END_DECLS
 
 #endif /* shadow.h */