closing FDs in optimized way

* code ported from sudo utility

configure.ac

@@ -577,6 +577,11 @@ AC_TYPE_SIZE_T
 AC_TYPE_UID_T
 AC_HEADER_TIME
 
+
+AH_TEMPLATE(HAVE_DD_FD, [Define to 1 if your `DIR' contains dd_fd.])
+AH_TEMPLATE(HAVE_DIRFD, [Define to 1 if you have the `dirfd' function or macro.])
+AH_TEMPLATE(HAVE_FCNTL_CLOSEM, [Define to 1 if your system has the F_CLOSEM fcntl.])
+
 #
 # Checks for library functions.
 #
@@ -1129,6 +1134,29 @@ AC_CHECK_FUNCS(getvfsstat, [have_getvfsstat="yes"])
 have_listmntent="no"
 AC_CHECK_FUNCS(listmntent, [have_listmntent="yes"])
 
+AC_CHECK_FUNCS(closefrom, [], [AC_LIBOBJ(closefrom)
+    AC_CHECK_DECL(F_CLOSEM, AC_DEFINE(HAVE_FCNTL_CLOSEM), [],
+  [ #include <limits.h>
+    #include <fcntl.h> ])
+])
+
+dnl
+dnl Check for the dirfd function/macro.  If not found, look for dd_fd in DIR.
+dnl
+AC_LINK_IFELSE([AC_LANG_PROGRAM([[#include <sys/types.h>
+#include <$ac_header_dirent>]], [[DIR *d; (void)dirfd(d);]])], [AC_DEFINE(HAVE_DIRFD)], [AC_LINK_IFELSE([AC_LANG_PROGRAM([[#include <sys/types.h>
+#include <$ac_header_dirent>]], [[DIR d; memset(&d, 0, sizeof(d)); return(d.dd_fd);]])], [AC_DEFINE(HAVE_DD_FD)], [])])
+AC_CHECK_MEMBERS([struct dirent.d_type], [], [], [
+AC_INCLUDES_DEFAULT
+#include <$ac_header_dirent>
+])
+
+AC_CHECK_FUNCS(closefrom, [], [AC_LIBOBJ(closefrom)
+    AC_CHECK_DECL(F_CLOSEM, AC_DEFINE(HAVE_FCNTL_CLOSEM), [],
+  [ #include <limits.h>
+    #include <fcntl.h> ])
+])
+
 have_getmntent="no"
 AC_CHECK_FUNCS(getmntent, [have_getmntent="c"])
 if test "x$have_getmntent" = "xno"; then

src/Makefile.am

@@ -22,6 +22,7 @@ bin_PROGRAMS = collectd-nagios collectdctl collectd-tg
 
 collectd_SOURCES = collectd.c collectd.h \
 		   common.c common.h \
+		   compat/closefrom.c \
 		   configfile.c configfile.h \
 		   filter_chain.c filter_chain.h \
 		   meta_data.c meta_data.h \
@@ -87,7 +88,7 @@ else
 collectd_LDADD += -loconfig
 endif
 
-collectdmon_SOURCES = collectdmon.c
+collectdmon_SOURCES = collectdmon.c compat/closefrom.c
 collectdmon_CPPFLAGS = $(AM_CPPFLAGS)
 
 collectd_nagios_SOURCES = collectd-nagios.c

src/collectdmon.c

@@ -50,6 +50,8 @@
 
 #include <unistd.h>
 
+#include "compat/missing.h"
+
 #ifndef COLLECTDMON_PIDFILE
 # define COLLECTDMON_PIDFILE LOCALSTATEDIR"/run/collectdmon.pid"
 #endif /* ! COLLECTDMON_PIDFILE */
@@ -116,7 +118,6 @@ static int daemonize (void)
 	struct rlimit rl;
 
 	pid_t pid = 0;
-	int   i   = 0;
 
 	if (0 != chdir ("/")) {
 		fprintf (stderr, "Error: chdir() failed: %s\n", strerror (errno));
@@ -141,11 +142,8 @@ static int daemonize (void)
 
 	setsid ();
 
-	if (RLIM_INFINITY == rl.rlim_max)
-		rl.rlim_max = 1024;
-
-	for (i = 0; i < (int)rl.rlim_max; ++i)
-		close (i);
+	/* Close all file descriptors in optimized way */
+	closefrom(0);
 
 	errno = 0;
 	if (open ("/dev/null", O_RDWR) != 0) {

src/compat/closefrom.c

@@ -0,0 +1,118 @@
+/*
+ * Copyright (c) 2004-2005, 2007, 2010
+ *	Todd C. Miller <Todd.Miller@courtesan.com>
+ *
+ * Permission to use, copy, modify, and distribute this software for any
+ * purpose with or without fee is hereby granted, provided that the above
+ * copyright notice and this permission notice appear in all copies.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
+ * WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
+ * MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
+ * ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
+ * WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
+ * ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
+ * OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
+ */
+
+#include <config.h>
+
+#include <sys/types.h>
+#include <sys/param.h>
+#include <unistd.h>
+#include <stdio.h>
+#ifdef STDC_HEADERS
+# include <stdlib.h>
+# include <stddef.h>
+#else
+# ifdef HAVE_STDLIB_H
+#  include <stdlib.h>
+# endif
+#endif /* STDC_HEADERS */
+#include <fcntl.h>
+#ifdef HAVE_DIRENT_H
+# include <dirent.h>
+# define NAMLEN(dirent) strlen((dirent)->d_name)
+#else
+# define dirent direct
+# define NAMLEN(dirent) (dirent)->d_namlen
+# ifdef HAVE_SYS_NDIR_H
+#  include <sys/ndir.h>
+# endif
+# ifdef HAVE_SYS_DIR_H
+#  include <sys/dir.h>
+# endif
+# ifdef HAVE_NDIR_H
+#  include <ndir.h>
+# endif
+#endif
+
+#include "missing.h"
+
+#ifndef HAVE_FCNTL_CLOSEM
+# ifndef HAVE_DIRFD
+#   define closefrom_fallback	closefrom
+# endif
+#endif
+
+/*
+ * Close all file descriptors greater than or equal to lowfd.
+ * This is the expensive (ballback) method.
+ */
+void
+closefrom_fallback(int lowfd)
+{
+    long fd, maxfd;
+
+    /*
+     * Fall back on sysconf() or getdtablesize().  We avoid checking
+     * resource limits since it is possible to open a file descriptor
+     * and then drop the rlimit such that it is below the open fd.
+     */
+#ifdef HAVE_SYSCONF
+    maxfd = sysconf(_SC_OPEN_MAX);
+#else
+    maxfd = getdtablesize();
+#endif /* HAVE_SYSCONF */
+    if (maxfd < 0)
+	maxfd = OPEN_MAX;
+
+    for (fd = lowfd; fd < maxfd; fd++)
+	(void) close((int) fd);
+}
+
+/*
+ * Close all file descriptors greater than or equal to lowfd.
+ * We try the fast way first, falling back on the slow method.
+ */
+#ifdef HAVE_FCNTL_CLOSEM
+void
+closefrom(int lowfd)
+{
+    if (fcntl(lowfd, F_CLOSEM, 0) == -1)
+	closefrom_fallback(lowfd);
+}
+#else
+# ifdef HAVE_DIRFD
+void
+closefrom(int lowfd)
+{
+    struct dirent *dent;
+    DIR *dirp;
+    char *endp;
+    long fd;
+
+    /* Use /proc/self/fd directory if it exists. */
+    if ((dirp = opendir("/proc/self/fd")) != NULL) {
+	while ((dent = readdir(dirp)) != NULL) {
+	    fd = strtol(dent->d_name, &endp, 10);
+	    if (dent->d_name != endp && *endp == '\0' &&
+		fd >= 0 && fd < INT_MAX && fd >= lowfd && fd != dirfd(dirp))
+		(void) close((int) fd);
+	}
+	(void) closedir(dirp);
+    } else
+	closefrom_fallback(lowfd);
+}
+#endif /* HAVE_DIRFD */
+#endif /* HAVE_FCNTL_CLOSEM */

src/compat/missing.h

@@ -0,0 +1,10 @@
+/*
+ * Some systems lack full limit definitions.
+ */
+#ifndef OPEN_MAX
+# define OPEN_MAX 256
+#endif
+
+#ifndef HAVE_CLOSEFROM
+void closefrom(int);
+#endif

src/exec.c

@@ -32,6 +32,8 @@
 #include "utils_cmd_putval.h"
 #include "utils_cmd_putnotif.h"
 
+#include "compat/missing.h"
+
 #include <sys/types.h>
 #include <pwd.h>
 #include <grp.h>
@@ -99,6 +101,14 @@ static void sigchld_handler (int __attribute__((unused)) signal) /* {{{ */
   } /* while (waitpid) */
 } /* void sigchld_handler }}} */
 
+static int int_max(int a, int b) {
+  if (a >= b) {
+    return a;
+  } else {
+    return b;
+  }
+}
+
 static int exec_config_exec (oconfig_item_t *ci) /* {{{ */
 {
   program_list_t *pl;
@@ -466,12 +476,14 @@ static int fork_child (program_list_t *pl, int *fd_in, int *fd_out, int *fd_err)
   }
   else if (pid == 0)
   {
-    int fd_num;
     int fd;
+    int fd_max_used = -1;
+
+    /* Determine the highest FD we need to keep */
+    fd_max_used = int_max(int_max(fd_pipe_in[0], fd_pipe_out[1]), fd_pipe_err[1]);
 
     /* Close all file descriptors but the pipe end we need. */
-    fd_num = getdtablesize ();
-    for (fd = 0; fd < fd_num; fd++)
+    for (fd = 0; fd < fd_max_used; fd++)
     {
       if ((fd == fd_pipe_in[0])
           || (fd == fd_pipe_out[1])
@@ -480,6 +492,9 @@ static int fork_child (program_list_t *pl, int *fd_in, int *fd_out, int *fd_err)
       close (fd);
     }
 
+    /* Close all other file descriptors in optimized way */
+    closefrom(fd_max_used + 1);
+
     /* Connect the `in' pipe to STDIN */
     if (fd_pipe_in[0] != STDIN_FILENO)
     {