summaryrefslogtreecommitdiffstats
path: root/libpam/pam_modutil_sanitize.c
blob: 65f85d011bfc9d7f954e2e563acea07b1c6c03e7 (plain)
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
/*
 * This file implements the following functions:
 *   pam_modutil_sanitize_helper_fds:
 *     redirects standard descriptors, closes all other descriptors.
 */

#include "pam_modutil_private.h"
#include <security/pam_ext.h>
#include <unistd.h>
#include <fcntl.h>
#include <syslog.h>
#include <sys/resource.h>

/*
 * Creates a pipe, closes its write end, redirects fd to its read end.
 * Returns fd on success, -1 otherwise.
 */
static int
redirect_in_pipe(pam_handle_t *pamh, int fd, const char *name)
{
	int in[2];

	if (pipe(in) < 0) {
		pam_syslog(pamh, LOG_ERR, "Could not create pipe: %m");
		return -1;
	}

	close(in[1]);

	if (in[0] == fd)
		return fd;

	if (dup2(in[0], fd) != fd) {
		pam_syslog(pamh, LOG_ERR, "dup2 of %s failed: %m", name);
		fd = -1;
	}

	close(in[0]);
	return fd;
}

/*
 * Creates a pipe, closes its read end, redirects fd to its write end.
 * Returns fd on success, -1 otherwise.
 */
static int
redirect_out_pipe(pam_handle_t *pamh, int fd, const char *name)
{
	int out[2];

	if (pipe(out) < 0) {
		pam_syslog(pamh, LOG_ERR, "Could not create pipe: %m");
		return -1;
	}

	close(out[0]);

	if (out[1] == fd)
		return fd;

	if (dup2(out[1], fd) != fd) {
		pam_syslog(pamh, LOG_ERR, "dup2 of %s failed: %m", name);
		fd = -1;
	}

	close(out[1]);
	return fd;
}

/*
 * Opens /dev/null for writing, redirects fd there.
 * Returns fd on success, -1 otherwise.
 */
static int
redirect_out_null(pam_handle_t *pamh, int fd, const char *name)
{
	int null = open("/dev/null", O_WRONLY);

	if (null < 0) {
		pam_syslog(pamh, LOG_ERR, "open of %s failed: %m", "/dev/null");
		return -1;
	}

	if (null == fd)
		return fd;

	if (dup2(null, fd) != fd) {
		pam_syslog(pamh, LOG_ERR, "dup2 of %s failed: %m", name);
		fd = -1;
	}

	close(null);
	return fd;
}

static int
redirect_out(pam_handle_t *pamh, enum pam_modutil_redirect_fd mode,
	     int fd, const char *name)
{
	switch (mode) {
		case PAM_MODUTIL_PIPE_FD:
			if (redirect_out_pipe(pamh, fd, name) < 0)
				return -1;
			break;
		case PAM_MODUTIL_NULL_FD:
			if (redirect_out_null(pamh, fd, name) < 0)
				return -1;
			break;
		case PAM_MODUTIL_IGNORE_FD:
			break;
	}
	return fd;
}

/* Closes all descriptors after stderr. */
static void
close_fds(void)
{
	/*
	 * An arbitrary upper limit for the maximum file descriptor number
	 * returned by RLIMIT_NOFILE.
	 */
	const int MAX_FD_NO = 65535;

	/* The lower limit is the same as for _POSIX_OPEN_MAX. */
	const int MIN_FD_NO = 20;

	int fd;
	struct rlimit rlim;

	if (getrlimit(RLIMIT_NOFILE, &rlim) || rlim.rlim_max > MAX_FD_NO)
		fd = MAX_FD_NO;
	else if (rlim.rlim_max < MIN_FD_NO)
		fd = MIN_FD_NO;
	else
		fd = rlim.rlim_max - 1;

	for (; fd > STDERR_FILENO; --fd)
		close(fd);
}

int
pam_modutil_sanitize_helper_fds(pam_handle_t *pamh,
				enum pam_modutil_redirect_fd stdin_mode,
				enum pam_modutil_redirect_fd stdout_mode,
				enum pam_modutil_redirect_fd stderr_mode)
{
	if (stdin_mode != PAM_MODUTIL_IGNORE_FD &&
	    redirect_in_pipe(pamh, STDIN_FILENO, "stdin") < 0) {
		return -1;
	}

	if (redirect_out(pamh, stdout_mode, STDOUT_FILENO, "stdout") < 0)
		return -1;

	/*
	 * If stderr should not be ignored and
	 * redirect mode for stdout and stderr are the same,
	 * optimize by redirecting stderr to stdout.
	 */
	if (stderr_mode != PAM_MODUTIL_IGNORE_FD &&
	    stdout_mode == stderr_mode) {
		if (dup2(STDOUT_FILENO, STDERR_FILENO) != STDERR_FILENO) {
			pam_syslog(pamh, LOG_ERR,
				   "dup2 of %s failed: %m", "stderr");
			return -1;
		}
	} else {
		if (redirect_out(pamh, stderr_mode, STDERR_FILENO, "stderr") < 0)
			return -1;
	}

	close_fds();
	return 0;
}