Parent: [ae3dbd] (diff)

Child: [27f1a6] (diff)

Download this file

closefrom.cpp    246 lines (214 with data), 6.7 kB

  1
  2
  3
  4
  5
  6
  7
  8
  9
 10
 11
 12
 13
 14
 15
 16
 17
 18
 19
 20
 21
 22
 23
 24
 25
 26
 27
 28
 29
 30
 31
 32
 33
 34
 35
 36
 37
 38
 39
 40
 41
 42
 43
 44
 45
 46
 47
 48
 49
 50
 51
 52
 53
 54
 55
 56
 57
 58
 59
 60
 61
 62
 63
 64
 65
 66
 67
 68
 69
 70
 71
 72
 73
 74
 75
 76
 77
 78
 79
 80
 81
 82
 83
 84
 85
 86
 87
 88
 89
 90
 91
 92
 93
 94
 95
 96
 97
 98
 99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
/* 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
*
* 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>
/* #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 (defined(linux) || defined(__linux))
/* 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 whatsoever.
*
* 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.
*/
static int closefrom_maxfd = -1;
#ifndef OPEN_MAX
#define OPEN_MAX 256 /* Guess */
#endif
void libclf_setmaxfd(int max)
{
closefrom_maxfd = max;
}
#ifdef sun
#include <limits.h>
#endif
int libclf_closefrom(int fd0)
{
int i, maxfd = closefrom_maxfd;
if (maxfd < 0) {
#ifdef _SC_OPEN_MAX
maxfd = sysconf(_SC_OPEN_MAX);
DPRINT((stderr, "Maxfd is %d after sysconf()\n", maxfd));
#else
maxfd = getdtablesize();
DPRINT((stderr, "Maxfd is %d after getdtablesize()\n", maxfd));
#endif
}
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
#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