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Re: [patch] who and stale utmp entries


From: Paul Eggert
Subject: Re: [patch] who and stale utmp entries
Date: Wed, 30 Mar 2005 00:31:06 -0500
User-agent: Gnus/5.1006 (Gnus v5.10.6) Emacs/21.4 (gnu/linux)

Tim Waugh <address@hidden> writes:

> Yes, this works very well.  Thanks!

You're welcome.  I installed the following slightly-modified patch:
it updates m4/readutmp.m4 as well, and it adds another check for
size_t overflow.

2005-03-30  Paul Eggert  <address@hidden>

        * lib/readutmp.h (read_utmp): New arg OPTIONS.  All uses changed.
        * lib/readutmp.c: Likewise.  Include signal.h, stdbool.h.
        (desirable_utmp_entry): New function.
        (read_utmp) [defined UTMP_NAME_FUNCTION]: Redo memory allocation
        using x2nrealloc, to simplify logic.
        (read_utmp) [!defined UTMP_NAME_FUNCTION]: Check for overflow in
        size calculation.
        * lib/readutmp.h (UT_PID): Moved here from ../src/who.c.
        (READ_UTMP_CHECK_PIDS): New constant.

        * m4/readutmp.m4 (gl_READUTMP): Require AC_C_INLINE.
        Use AC_CHECK_HEADERS_ONCE and AC_CHECK_FUNCS_ONCE when possible.
        Remove duplicate call to AC_LIBOBJ(readutmp).
        (gl_PREREQ_READUTMP): Remove.  All uses removed.  This module
        no longer relies on free (NULL) working.

        * src/pinky.c (short_pinky): Adjust to read_utmp signature change.
        * src/uptime.c (uptime): New arg OPTIONS.  All uses changed.
        * src/users.c (users): Likewise.
        * src/who.c (who): Likewise.
        * src/uptime.c (main): Check PIDs when invoked with zero arguments.
        * src/users.c (main): Likewise.
        * src/who.c (main): Likewise.  Also with two arguments.
        Omit duplicate code in 2-arg case.
        (UT_PID): Moved to ../lib/readutmp.h.

Index: lib/readutmp.c
===================================================================
RCS file: /fetish/cu/lib/readutmp.c,v
retrieving revision 1.23
diff -p -u -r1.23 readutmp.c
--- lib/readutmp.c      30 Nov 2004 21:39:26 -0000      1.23
+++ lib/readutmp.c      30 Mar 2005 05:15:40 -0000
@@ -1,5 +1,5 @@
 /* GNU's read utmp module.
-   Copyright (C) 1992-2001, 2003, 2004 Free Software Foundation, Inc.
+   Copyright (C) 1992-2001, 2003, 2004, 2005 Free Software Foundation, Inc.
 
    This program is free software; you can redistribute it and/or modify
    it under the terms of the GNU General Public License as published by
@@ -26,6 +26,8 @@
 
 #include <sys/types.h>
 #include <sys/stat.h>
+#include <signal.h>
+#include <stdbool.h>
 #include <string.h>
 #include <stdlib.h>
 
@@ -35,6 +37,10 @@
 # include "unlocked-io.h"
 #endif
 
+#ifndef SIZE_MAX
+# define SIZE_MAX ((size_t) -1)
+#endif
+
 /* Copy UT->ut_name into storage obtained from malloc.  Then remove any
    trailing spaces from the copy, NUL terminate it, and return the copy.  */
 
@@ -56,19 +62,32 @@ extract_trimmed_name (const STRUCT_UTMP 
   return trimmed_name;
 }
 
+/* Is the utmp entry U desired by the user who asked for OPTIONS?  */
+
+static inline bool
+desirable_utmp_entry (STRUCT_UTMP const *u, int options)
+{
+  return ! (options & READ_UTMP_CHECK_PIDS
+           && (UT_PID (u) <= 0
+               || (kill (UT_PID (u), 0) < 0 && errno == ESRCH)));
+}
+
 /* Read the utmp entries corresponding to file FILENAME into freshly-
    malloc'd storage, set *UTMP_BUF to that pointer, set *N_ENTRIES to
    the number of entries, and return zero.  If there is any error,
-   return -1, setting errno, and don't modify the parameters.  */
+   return -1, setting errno, and don't modify the parameters.
+   If OPTIONS & READ_UTMP_CHECK_PIDS is nonzero, omit entries whose
+   process-IDs do not currently exist.  */
 
 #ifdef UTMP_NAME_FUNCTION
 
 int
-read_utmp (const char *filename, size_t *n_entries, STRUCT_UTMP **utmp_buf)
+read_utmp (const char *filename, size_t *n_entries, STRUCT_UTMP **utmp_buf,
+          int options)
 {
-  size_t n_read;
-  size_t n_alloc = 4;
-  STRUCT_UTMP *utmp = xmalloc (n_alloc * sizeof *utmp);
+  size_t n_read = 0;
+  size_t n_alloc = 0;
+  STRUCT_UTMP *utmp = NULL;
   STRUCT_UTMP *u;
 
   /* Ignore the return value for now.
@@ -79,17 +98,14 @@ read_utmp (const char *filename, size_t 
 
   SET_UTMP_ENT ();
 
-  n_read = 0;
   while ((u = GET_UTMP_ENT ()) != NULL)
-    {
-      if (n_read == n_alloc)
-       {
-         utmp = xnrealloc (utmp, n_alloc, 2 * sizeof *utmp);
-         n_alloc *= 2;
-       }
-      ++n_read;
-      utmp[n_read - 1] = *u;
-    }
+    if (desirable_utmp_entry (u, options))
+      {
+       if (n_read == n_alloc)
+         utmp = x2nrealloc (utmp, &n_alloc, sizeof *utmp);
+
+       utmp[n_read++] = *u;
+      }
 
   END_UTMP_ENT ();
 
@@ -108,6 +124,8 @@ read_utmp (const char *filename, size_t 
   struct stat file_stats;
   size_t n_read;
   size_t size;
+  size_t i;
+  size_t n_desired;
   STRUCT_UTMP *buf;
 
   utmp = fopen (filename, "r");
@@ -121,6 +139,8 @@ read_utmp (const char *filename, size_t 
       errno = e;
       return -1;
     }
+  if (! (0 <= file_stats.st_size && file_stats.st_size <= SIZE_MAX))
+    xalloc_die ();
   size = file_stats.st_size;
   buf = xmalloc (size);
   n_read = fread (buf, sizeof *buf, size / sizeof *buf, utmp);
@@ -140,7 +160,12 @@ read_utmp (const char *filename, size_t 
       return -1;
     }
 
-  *n_entries = n_read;
+  n_desired = 0;
+  for (i = 0; i < n_read; i++)
+    if (desirable_utmp_entry (&utmp[i], options))
+      utmp[n_desired++] = utmp[i];
+
+  *n_entries = n_desired;
   *utmp_buf = buf;
 
   return 0;
Index: lib/readutmp.h
===================================================================
RCS file: /fetish/cu/lib/readutmp.h,v
retrieving revision 1.18
diff -p -u -r1.18 readutmp.h
--- lib/readutmp.h      1 Dec 2004 07:07:38 -0000       1.18
+++ lib/readutmp.h      30 Mar 2005 05:15:40 -0000
@@ -1,7 +1,7 @@
 /* Declarations for GNU's read utmp module.
 
    Copyright (C) 1992, 1993, 1994, 1995, 1996, 1997, 1998, 1999, 2000,
-   2001, 2002, 2003, 2004 Free Software Foundation, Inc.
+   2001, 2002, 2003, 2004, 2005 Free Software Foundation, Inc.
 
    This program is free software; you can redistribute it and/or modify
    it under the terms of the GNU General Public License as published by
@@ -167,6 +167,12 @@ enum { UT_USER_SIZE = sizeof UT_USER ((S
 #  define WTMP_FILE "/etc/wtmp"
 # endif
 
+# if HAVE_STRUCT_XTMP_UT_PID
+#  define UT_PID(U) ((U)->ut_pid)
+# else
+#  define UT_PID(U) 0
+# endif
+
 # if HAVE_STRUCT_UTMP_UT_TYPE || HAVE_STRUCT_UTMPX_UT_TYPE
 #  define UT_TYPE_EQ(U, V) ((U)->ut_type == (V))
 #  define UT_TYPE_NOT_DEFINED 0
@@ -192,7 +198,14 @@ enum { UT_USER_SIZE = sizeof UT_USER ((S
     && (UT_TYPE_USER_PROCESS (U)                               \
         || (UT_TYPE_NOT_DEFINED && UT_TIME_MEMBER (U) != 0)))
 
+/* Options for read_utmp.  */
+enum
+  {
+    READ_UTMP_CHECK_PIDS = 1
+  };
+
 char *extract_trimmed_name (const STRUCT_UTMP *ut);
-int read_utmp (const char *filename, size_t *n_entries, STRUCT_UTMP 
**utmp_buf);
+int read_utmp (const char *filename, size_t *n_entries, STRUCT_UTMP **utmp_buf,
+              int options);
 
 #endif /* __READUTMP_H__ */
Index: m4/readutmp.m4
===================================================================
RCS file: /fetish/cu/m4/readutmp.m4,v
retrieving revision 1.6
diff -p -u -r1.6 readutmp.m4
--- m4/readutmp.m4      29 Jan 2005 00:16:39 -0000      1.6
+++ m4/readutmp.m4      30 Mar 2005 05:15:40 -0000
@@ -1,4 +1,4 @@
-# readutmp.m4 serial 7
+# readutmp.m4 serial 8
 dnl Copyright (C) 2002, 2003, 2004, 2005 Free Software Foundation, Inc.
 dnl This file is free software; the Free Software Foundation
 dnl gives unlimited permission to copy and/or distribute it,
@@ -10,8 +10,9 @@ AC_DEFUN([gl_READUTMP],
   AC_LIBOBJ([readutmp])
 
   dnl Prerequisites of lib/readutmp.h.
-  AC_CHECK_HEADERS(utmp.h utmpx.h)
-  AC_CHECK_FUNCS(utmpname utmpxname)
+  AC_REQUIRE([AC_C_INLINE])
+  AC_CHECK_HEADERS_ONCE(utmp.h utmpx.h)
+  AC_CHECK_FUNCS_ONCE(utmpname utmpxname)
   AC_CHECK_DECLS(getutent,,,[
 #ifdef HAVE_UTMP_H
 # include <utmp.h>
@@ -49,14 +50,5 @@ $ac_includes_default
     AC_CHECK_MEMBERS([struct utmp.ut_exit.ut_termination],,,[$utmp_includes])
     AC_CHECK_MEMBERS([struct utmpx.ut_exit.e_termination],,,[$utmp_includes])
     AC_CHECK_MEMBERS([struct utmp.ut_exit.e_termination],,,[$utmp_includes])
-
-    AC_LIBOBJ(readutmp)
-    gl_PREREQ_READUTMP
   fi
 ])
-
-# Prerequisites of lib/readutmp.c.
-AC_DEFUN([gl_PREREQ_READUTMP],
-[
-  AC_REQUIRE([gl_FUNC_FREE])
-])
Index: src/pinky.c
===================================================================
RCS file: /fetish/cu/src/pinky.c,v
retrieving revision 1.45
diff -p -u -r1.45 pinky.c
--- src/pinky.c 28 Mar 2005 18:06:55 -0000      1.45
+++ src/pinky.c 30 Mar 2005 05:15:41 -0000
@@ -488,7 +488,7 @@ short_pinky (const char *filename,
   size_t n_users;
   STRUCT_UTMP *utmp_buf;
 
-  if (read_utmp (filename, &n_users, &utmp_buf) != 0)
+  if (read_utmp (filename, &n_users, &utmp_buf, 0) != 0)
     error (EXIT_FAILURE, errno, "%s", filename);
 
   scan_entries (n_users, utmp_buf, argc_names, argv_names);
Index: src/uptime.c
===================================================================
RCS file: /fetish/cu/src/uptime.c,v
retrieving revision 1.49
diff -p -u -r1.49 uptime.c
--- src/uptime.c        28 Mar 2005 18:15:16 -0000      1.49
+++ src/uptime.c        30 Mar 2005 05:15:41 -0000
@@ -154,15 +154,16 @@ print_uptime (size_t n, const STRUCT_UTM
 }
 
 /* Display the system uptime and the number of users on the system,
-   according to utmp file FILENAME. */
+   according to utmp file FILENAME.  Use read_utmp OPTIONS to read the
+   utmp file.  */
 
 static void
-uptime (const char *filename)
+uptime (const char *filename, int options)
 {
   size_t n_users;
   STRUCT_UTMP *utmp_buf;
 
-  if (read_utmp (filename, &n_users, &utmp_buf) != 0)
+  if (read_utmp (filename, &n_users, &utmp_buf, options) != 0)
     error (EXIT_FAILURE, errno, "%s", filename);
 
   print_uptime (n_users, utmp_buf);
@@ -211,11 +212,11 @@ main (int argc, char **argv)
   switch (argc - optind)
     {
     case 0:                    /* uptime */
-      uptime (UTMP_FILE);
+      uptime (UTMP_FILE, READ_UTMP_CHECK_PIDS);
       break;
 
     case 1:                    /* uptime <utmp file> */
-      uptime (argv[optind]);
+      uptime (argv[optind], 0);
       break;
 
     default:                   /* lose */
Index: src/users.c
===================================================================
RCS file: /fetish/cu/src/users.c,v
retrieving revision 1.39
diff -p -u -r1.39 users.c
--- src/users.c 30 Nov 2004 21:40:52 -0000      1.39
+++ src/users.c 30 Mar 2005 05:15:41 -0000
@@ -1,5 +1,5 @@
 /* GNU's users.
-   Copyright (C) 1992-2004 Free Software Foundation, Inc.
+   Copyright (C) 1992-2005 Free Software Foundation, Inc.
 
    This program is free software; you can redistribute it and/or modify
    it under the terms of the GNU General Public License as published by
@@ -80,15 +80,16 @@ list_entries_users (size_t n, const STRU
   free (u);
 }
 
-/* Display a list of users on the system, according to utmp file FILENAME. */
+/* Display a list of users on the system, according to utmp file FILENAME.
+   Use read_utmp OPTIONS to read FILENAME.  */
 
 static void
-users (const char *filename)
+users (const char *filename, int options)
 {
   size_t n_users;
   STRUCT_UTMP *utmp_buf;
 
-  if (read_utmp (filename, &n_users, &utmp_buf) != 0)
+  if (read_utmp (filename, &n_users, &utmp_buf, options) != 0)
     error (EXIT_FAILURE, errno, "%s", filename);
 
   list_entries_users (n_users, utmp_buf);
@@ -137,11 +138,11 @@ main (int argc, char **argv)
   switch (argc - optind)
     {
     case 0:                    /* users */
-      users (UTMP_FILE);
+      users (UTMP_FILE, READ_UTMP_CHECK_PIDS);
       break;
 
     case 1:                    /* users <utmp file> */
-      users (argv[optind]);
+      users (argv[optind], 0);
       break;
 
     default:                   /* lose */
Index: src/who.c
===================================================================
RCS file: /fetish/cu/src/who.c,v
retrieving revision 1.106
diff -p -u -r1.106 who.c
--- src/who.c   28 Mar 2005 18:16:06 -0000      1.106
+++ src/who.c   30 Mar 2005 05:15:41 -0000
@@ -84,12 +84,10 @@
 #define IDLESTR_LEN 6
 
 #if HAVE_STRUCT_XTMP_UT_PID
-# define UT_PID(U) ((U)->ut_pid)
 # define PIDSTR_DECL_AND_INIT(Var, Utmp_ent) \
   char Var[INT_STRLEN_BOUND (Utmp_ent->ut_pid) + 1]; \
   sprintf (Var, "%ld", (long int) (Utmp_ent->ut_pid))
 #else
-# define UT_PID(U) 0
 # define PIDSTR_DECL_AND_INIT(Var, Utmp_ent) \
   const char *Var = ""
 #endif
@@ -607,14 +605,15 @@ scan_entries (size_t n, const STRUCT_UTM
     }
 }
 
-/* Display a list of who is on the system, according to utmp file filename. */
+/* Display a list of who is on the system, according to utmp file FILENAME.
+   Use read_utmp OPTIONS to read the file.  */
 static void
-who (const char *filename)
+who (const char *filename, int options)
 {
   size_t n_users;
   STRUCT_UTMP *utmp_buf;
 
-  if (read_utmp (filename, &n_users, &utmp_buf) != 0)
+  if (read_utmp (filename, &n_users, &utmp_buf, options) != 0)
     error (EXIT_FAILURE, errno, "%s", filename);
 
   if (short_list)
@@ -811,18 +810,16 @@ main (int argc, char **argv)
 
   switch (argc - optind)
     {
+    case 2:                    /* who <blurf> <glop> */
+      my_line_only = true;
+      /* Fall through.  */
     case -1:
     case 0:                    /* who */
-      who (UTMP_FILE);
+      who (UTMP_FILE, READ_UTMP_CHECK_PIDS);
       break;
 
     case 1:                    /* who <utmp file> */
-      who (argv[optind]);
-      break;
-
-    case 2:                    /* who <blurf> <glop> */
-      my_line_only = true;
-      who (UTMP_FILE);
+      who (argv[optind], 0);
       break;
 
     default:                   /* lose */




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