/* Copyright (C) 2009 J.F.Dockes
* 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
* the Free Software Foundation; either version 2 of the License, or
* (at your option) any later version.
*
* This program 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 General Public License for more details.
*
* You should have received a copy of the GNU General Public License
* along with this program; if not, write to the
* Free Software Foundation, Inc.,
* 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA.
*/
/*
* Close all file descriptors above a given value.
*
* A Unix execXX() call used to execute another program does not close open
* file descriptors by default.
*
* The only descriptors closed are those on which the FD_CLOEXEC flag was
* set. FD_CLOEXEC is not easily usable on files opened by external
* libraries.
*
* There are many reasons for closing file descriptors before
* an exec (security, pipe control, the possibility that a bug will trigger
* an unwanted write, etc.)
*
* A process has currently no POSIX way to determine the set of open file
* descriptors or at least the highest value. Closing all files (except a few),
* thus implies performing a close() system call on each entry up to the
* maximum, which can be both relatively difficult to determine, and quite
* high (ie: several thousands), incurring a non-negligible cost.
*
* A number of systems have non-portable support for mitigating or solving
* this problem.
*
* This module supplies a portable interface to this functionality.
*
* The initial data on system interfaces was obtained from:
* http://stackoverflow.com/questions/899038/\
* getting-the-highest-allocated-file-descriptor
*
* System interfaces:
* FreeBSD:
* - Has a closefrom() system call as of release 7.x around Sep 2009
* - Has a /dev/fd, directory which shows the current process' open
* descriptors. Only descriptors 0, 1, 2 are shown except if
* fdescfs is mounted which it is not by default
*
* Solaris:
* - Solaris 10+ has closefrom, and can specify closefrom to posix_spawn()
*
* Linux:
* - Has nothing. The method we used (opening /dev/fd) was very
* unsafe in multithread fork/exec context. We now use a close()
* loop. glibc maintainers think that closefrom() is a bad idea
* *especially* because it is implemented on *BSD and Solaris. Go
* figure...: https://sourceware.org/bugzilla/show_bug.cgi?id=10353
*
* Interface:
*
* int libclf_closefrom(fd)
* @param fd All open file descriptors with equal or higher numeric
* values will be closed. fd needs not be a valid descriptor.
* @return 0 for success, -1 for error.
*/
#ifndef TEST_CLOSEFROM
#include <stdio.h>
#include <unistd.h>
#include <fcntl.h>
#include <string.h>
#include <sys/param.h>
#include <sys/time.h>
#include <sys/resource.h>
#include "closefrom.h"
/* #define DEBUG_CLOSEFROM */
#ifdef DEBUG_CLOSEFROM
#define DPRINT(X) fprintf X
#else
#define DPRINT(X)
#endif
/* Note: sudo has a closefrom implementation, needs a lot of autoconfig, but
* we could use it instead. It's quite close to this though */
/*************************************************************************/
/* closefrom() exists on Solaris, netbsd and openbsd, but someone will
* have to provide me the appropriate macro to test */
#if (defined(__FreeBSD__) && __FreeBSD_version >= 702104)
/* Use closefrom() system call */
int libclf_closefrom(int fd0)
{
DPRINT((stderr, "libclf_closefrom: using closefrom(2)\n"));
closefrom(fd0);
return 0;
}
/*************************************************************************/
#elif defined(F_CLOSEM)
/* Use fcntl(fd, F_CLOSEM) */
int libclf_closefrom(int fd0)
{
DPRINT((stderr, "libclf_closefrom: using fcntl(F_CLOSEM)\n"));
// We need a valid descriptor for this to work. Try to dup stdin, else
// go wild
if (fcntl(0, F_GETFL) != -1) {
if (fd0 != 0)
dup2(0, fd0);
} else {
int fd = open("/etc/group", 0); // yes i am a unix man
if (fd >= 0 && fd != fd0) {
dup2(fd, fd0);
close(fd);
}
}
return fcntl(fd0, F_CLOSEM, 0);
}
/*************************************************************************/
#elif 0 && (defined(linux) || defined(__linux))
/* We don't do this on linux anymore because opendir() may call
malloc which is unsafe in the [fork-exec] interval for a
multithreaded program. Linux does not have a good solution for
implementing closefrom as far as I know */
/* Use /proc/self/fd directory */
#include <sys/types.h>
#include <dirent.h>
int libclf_closefrom(int fd0)
{
DIR *dirp;
struct dirent *ent;
DPRINT((stderr, "libclf_closefrom: using /proc\n"));
dirp = opendir("/proc/self/fd");
if (dirp == 0)
return -1;
while ((ent = readdir(dirp)) != 0) {
int fd;
if (!strcmp(ent->d_name, ".") || !strcmp(ent->d_name, ".."))
continue;
if (sscanf(ent->d_name, "%d", &fd) == 1 && fd >= fd0 &&
fd != dirfd(dirp)) {
close(fd);
}
}
closedir(dirp);
return 0;
}
/*************************************************************************/
#else
/* System has no native support for this functionality.
*
* Close all descriptors up to compiled/configured maximum.
* The caller will usually have an idea of a reasonable maximum, else
* we retrieve a value from the system.
*
* Note that there is actually no real guarantee that no open
* descriptor higher than the reported limit can exist, as noted by
* the Solaris man page for closefrom()
*/
static int closefrom_maxfd = -1;
void libclf_setmaxfd(int max)
{
closefrom_maxfd = max;
}
#include <limits.h>
#ifndef OPEN_MAX
#define OPEN_MAX 1024
#endif
int libclf_closefrom(int fd0)
{
int i, maxfd = closefrom_maxfd;
if (maxfd < 0) {
maxfd = libclf_maxfd();
}
if (maxfd < 0)
maxfd = OPEN_MAX;
DPRINT((stderr, "libclf_closefrom: using loop to %d\n", maxfd));
for (i = fd0; i < maxfd; i++) {
(void)close(i);
}
return 0;
}
#endif
int libclf_maxfd(int)
{
struct rlimit lim;
getrlimit(RLIMIT_NOFILE, &lim);
return int(lim.rlim_cur);
}
#else /* TEST_CLOSEFROM */
#include <stdio.h>
#include <unistd.h>
#include <fcntl.h>
#include <stdlib.h>
#include "closefrom.h"
int main(int argc, char **argv)
{
int i;
int fd0 = open("/etc/group", 0);
if (fd0 < 0) {
perror("open /etc/group");
exit(1);
}
if (dup2(fd0, 11) < 0) {
perror("dup2->11");
exit(1);
}
if (dup2(fd0, 19) < 0) {
perror("dup2->19");
exit(1);
}
if (dup2(fd0, 99)< 0) {
perror("dup2->99 (ok)");
}
if (dup2(fd0, 999) < 0) {
perror("dup3->999 (ok)");
}
libclf_closefrom(11);
for (i = 0; i < 10000; i++) {
if (fcntl(i, F_GETFL) != -1) {
fprintf(stderr, "Descriptor %d is still open", i);
if (i < 11)
fprintf(stderr, " (OK)\n");
else
fprintf(stderr, " (BAD)\n");
}
}
exit(0);
}
#endif