summaryrefslogtreecommitdiff
path: root/src/core/selinux-access.c
blob: 0f8a2d68e29e6de27a4559e915a27ea98cb4e06d (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
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
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
/***
  This file is part of systemd.

  Copyright 2012 Dan Walsh

  systemd is free software; you can redistribute it and/or modify it
  under the terms of the GNU Lesser General Public License as published by
  the Free Software Foundation; either version 2.1 of the License, or
  (at your option) any later version.

  systemd 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
  Lesser General Public License for more details.

  You should have received a copy of the GNU Lesser General Public License
  along with systemd; If not, see <http://www.gnu.org/licenses/>.
***/

#include "selinux-access.h"

#ifdef HAVE_SELINUX

#include <errno.h>
#include <selinux/avc.h>
#include <selinux/selinux.h>
#include <stdio.h>
#ifdef HAVE_AUDIT
#include <libaudit.h>
#endif

#include "sd-bus.h"

#include "alloc-util.h"
#include "audit-fd.h"
#include "bus-util.h"
#include "log.h"
#include "path-util.h"
#include "selinux-util.h"
#include "stdio-util.h"
#include "strv.h"
#include "util.h"

static bool initialized = false;

struct audit_info {
        sd_bus_creds *creds;
        const char *path;
        const char *cmdline;
};

/*
   Any time an access gets denied this callback will be called
   with the audit data.  We then need to just copy the audit data into the msgbuf.
*/
static int audit_callback(
                void *auditdata,
                security_class_t cls,
                char *msgbuf,
                size_t msgbufsize) {

        const struct audit_info *audit = auditdata;
        uid_t uid = 0, login_uid = 0;
        gid_t gid = 0;
        char login_uid_buf[DECIMAL_STR_MAX(uid_t) + 1] = "n/a";
        char uid_buf[DECIMAL_STR_MAX(uid_t) + 1] = "n/a";
        char gid_buf[DECIMAL_STR_MAX(gid_t) + 1] = "n/a";

        if (sd_bus_creds_get_audit_login_uid(audit->creds, &login_uid) >= 0)
                xsprintf(login_uid_buf, UID_FMT, login_uid);
        if (sd_bus_creds_get_euid(audit->creds, &uid) >= 0)
                xsprintf(uid_buf, UID_FMT, uid);
        if (sd_bus_creds_get_egid(audit->creds, &gid) >= 0)
                xsprintf(gid_buf, GID_FMT, gid);

        snprintf(msgbuf, msgbufsize,
                 "auid=%s uid=%s gid=%s%s%s%s%s%s%s",
                 login_uid_buf, uid_buf, gid_buf,
                 audit->path ? " path=\"" : "", strempty(audit->path), audit->path ? "\"" : "",
                 audit->cmdline ? " cmdline=\"" : "", strempty(audit->cmdline), audit->cmdline ? "\"" : "");

        return 0;
}

static int callback_type_to_priority(int type) {
        switch(type) {

        case SELINUX_ERROR:
                return LOG_ERR;

        case SELINUX_WARNING:
                return LOG_WARNING;

        case SELINUX_INFO:
                return LOG_INFO;

        case SELINUX_AVC:
        default:
                return LOG_NOTICE;
        }
}

/*
   libselinux uses this callback when access gets denied or other
   events happen. If audit is turned on, messages will be reported
   using audit netlink, otherwise they will be logged using the usual
   channels.

   Code copied from dbus and modified.
*/
_printf_(2, 3) static int log_callback(int type, const char *fmt, ...) {
        va_list ap;
        const char *fmt2;

#ifdef HAVE_AUDIT
        int fd;

        fd = get_audit_fd();

        if (fd >= 0) {
                _cleanup_free_ char *buf = NULL;
                int r;

                va_start(ap, fmt);
                r = vasprintf(&buf, fmt, ap);
                va_end(ap);

                if (r >= 0) {
                        audit_log_user_avc_message(fd, AUDIT_USER_AVC, buf, NULL, NULL, NULL, 0);
                        return 0;
                }
        }
#endif

        fmt2 = strjoina("selinux: ", fmt);

        va_start(ap, fmt);
#pragma GCC diagnostic push
#pragma GCC diagnostic ignored "-Wformat-nonliteral"
        log_internalv(LOG_AUTH | callback_type_to_priority(type),
                      0, __FILE__, __LINE__, __FUNCTION__,
                      fmt2, ap);
#pragma GCC diagnostic pop
        va_end(ap);

        return 0;
}

static int access_init(sd_bus_error *error) {

        if (!mac_selinux_use())
                return 0;

        if (initialized)
                return 1;

        if (avc_open(NULL, 0) != 0) {
                int enforce, saved_errno = errno;

                enforce = security_getenforce();
                log_full_errno(enforce != 0 ? LOG_ERR : LOG_WARNING, saved_errno, "Failed to open the SELinux AVC: %m");

                /* If enforcement isn't on, then let's suppress this
                 * error, and just don't do any AVC checks. The
                 * warning we printed is hence all the admin will
                 * see. */
                if (enforce == 0)
                        return 0;

                /* Return an access denied error, if we couldn't load
                 * the AVC but enforcing mode was on, or we couldn't
                 * determine whether it is one. */
                return sd_bus_error_setf(error, SD_BUS_ERROR_ACCESS_DENIED, "Failed to open the SELinux AVC: %s", strerror(saved_errno));
        }

        selinux_set_callback(SELINUX_CB_AUDIT, (union selinux_callback) audit_callback);
        selinux_set_callback(SELINUX_CB_LOG, (union selinux_callback) log_callback);

        initialized = true;
        return 1;
}

/*
   This function communicates with the kernel to check whether or not it should
   allow the access.
   If the machine is in permissive mode it will return ok.  Audit messages will
   still be generated if the access would be denied in enforcing mode.
*/
int mac_selinux_generic_access_check(
                sd_bus_message *message,
                const char *path,
                const char *permission,
                sd_bus_error *error) {

        _cleanup_(sd_bus_creds_unrefp) sd_bus_creds *creds = NULL;
        const char *tclass = NULL, *scon = NULL;
        struct audit_info audit_info = {};
        _cleanup_free_ char *cl = NULL;
        char *fcon = NULL;
        char **cmdline = NULL;
        int r = 0;

        assert(message);
        assert(permission);
        assert(error);

        r = access_init(error);
        if (r <= 0)
                return r;

        r = sd_bus_query_sender_creds(
                        message,
                        SD_BUS_CREDS_PID|SD_BUS_CREDS_EUID|SD_BUS_CREDS_EGID|
                        SD_BUS_CREDS_CMDLINE|SD_BUS_CREDS_AUDIT_LOGIN_UID|
                        SD_BUS_CREDS_SELINUX_CONTEXT|
                        SD_BUS_CREDS_AUGMENT /* get more bits from /proc */,
                        &creds);
        if (r < 0)
                goto finish;

        /* The SELinux context is something we really should have
         * gotten directly from the message or sender, and not be an
         * augmented field. If it was augmented we cannot use it for
         * authorization, since this is racy and vulnerable. Let's add
         * an extra check, just in case, even though this really
         * shouldn't be possible. */
        assert_return((sd_bus_creds_get_augmented_mask(creds) & SD_BUS_CREDS_SELINUX_CONTEXT) == 0, -EPERM);

        r = sd_bus_creds_get_selinux_context(creds, &scon);
        if (r < 0)
                goto finish;

        if (path) {
                /* Get the file context of the unit file */

                r = getfilecon_raw(path, &fcon);
                if (r < 0) {
                        r = sd_bus_error_setf(error, SD_BUS_ERROR_ACCESS_DENIED, "Failed to get file context on %s.", path);
                        goto finish;
                }

                tclass = "service";
        } else {
                r = getcon_raw(&fcon);
                if (r < 0) {
                        r = sd_bus_error_setf(error, SD_BUS_ERROR_ACCESS_DENIED, "Failed to get current context.");
                        goto finish;
                }

                tclass = "system";
        }

        sd_bus_creds_get_cmdline(creds, &cmdline);
        cl = strv_join(cmdline, " ");

        audit_info.creds = creds;
        audit_info.path = path;
        audit_info.cmdline = cl;

        r = selinux_check_access(scon, fcon, tclass, permission, &audit_info);
        if (r < 0)
                r = sd_bus_error_setf(error, SD_BUS_ERROR_ACCESS_DENIED, "SELinux policy denies access.");

        log_debug("SELinux access check scon=%s tcon=%s tclass=%s perm=%s path=%s cmdline=%s: %i", scon, fcon, tclass, permission, path, cl, r);

finish:
        freecon(fcon);

        if (r < 0 && security_getenforce() != 1) {
                sd_bus_error_free(error);
                r = 0;
        }

        return r;
}

#else

int mac_selinux_generic_access_check(
                sd_bus_message *message,
                const char *path,
                const char *permission,
                sd_bus_error *error) {

        return 0;
}

#endif