1/***
2  This file is part of avahi.
3
4  avahi is free software; you can redistribute it and/or modify it
5  under the terms of the GNU Lesser General Public License as
6  published by the Free Software Foundation; either version 2.1 of the
7  License, or (at your option) any later version.
8
9  avahi is distributed in the hope that it will be useful, but WITHOUT
10  ANY WARRANTY; without even the implied warranty of MERCHANTABILITY
11  or FITNESS FOR A PARTICULAR PURPOSE. See the GNU Lesser General
12  Public License for more details.
13
14  You should have received a copy of the GNU Lesser General Public
15  License along with avahi; if not, write to the Free Software
16  Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307
17  USA.
18***/
19
20#ifdef HAVE_CONFIG_H
21#include <config.h>
22#endif
23
24#include <sys/types.h>
25#include <assert.h>
26#include <errno.h>
27#include <string.h>
28#include <sys/capability.h>
29#include <sys/prctl.h>
30
31#include <avahi-core/log.h>
32
33#include "caps.h"
34
35int avahi_caps_reduce(void) {
36    int ret = 0;
37    cap_t caps;
38    static cap_value_t cap_values[] = { CAP_SYS_CHROOT, CAP_SETUID, CAP_SETGID };
39
40    /* Let's reduce our caps to the minimum set and tell Linux to keep
41     * them across setuid(). This is called before we drop
42     * privileges. */
43
44    caps = cap_init();
45    assert(caps);
46    cap_clear(caps);
47
48    cap_set_flag(caps, CAP_EFFECTIVE, 3, cap_values, CAP_SET);
49    cap_set_flag(caps, CAP_PERMITTED, 3, cap_values, CAP_SET);
50
51    if (cap_set_proc(caps) < 0) {
52        avahi_log_error("cap_set_proc() failed: %s", strerror(errno));
53        ret = -1;
54    }
55    cap_free(caps);
56
57    /* Retain capabilities across setuid() */
58    if (prctl(PR_SET_KEEPCAPS, 1, 0, 0, 0) < 0) {
59        avahi_log_error("prctl(PR_SET_KEEPCAPS) failed: %s", strerror(errno));
60        ret = -1;
61    }
62
63    return ret;
64}
65
66int avahi_caps_reduce2(void) {
67    int ret = 0;
68    cap_t caps;
69    static cap_value_t cap_values[] = { CAP_SYS_CHROOT };
70
71    /* Reduce our caps to the bare minimum and tell Linux not to keep
72     * them across setuid(). This is called after we drop
73     * privileges. */
74
75    /* No longer retain caps across setuid() */
76    if (prctl(PR_SET_KEEPCAPS, 0, 0, 0, 0) < 0) {
77        avahi_log_error("prctl(PR_SET_KEEPCAPS) failed: %s", strerror(errno));
78        ret = -1;
79    }
80
81    caps = cap_init();
82    assert(caps);
83    cap_clear(caps);
84
85    /* setuid() zeroed our effective caps, let's get them back */
86    cap_set_flag(caps, CAP_EFFECTIVE, 1, cap_values, CAP_SET);
87    cap_set_flag(caps, CAP_PERMITTED, 1, cap_values, CAP_SET);
88
89    if (cap_set_proc(caps) < 0) {
90        avahi_log_error("cap_set_proc() failed: %s", strerror(errno));
91        ret = -1;
92    }
93    cap_free(caps);
94
95    return ret;
96}
97
98int avahi_caps_drop_all(void) {
99    cap_t caps;
100    int ret = 0;
101
102    /* Drop all capabilities and turn ourselves into a normal user process */
103
104    caps = cap_init();
105    assert(caps);
106    cap_clear(caps);
107
108    if (cap_set_proc(caps) < 0) {
109        avahi_log_error("cap_set_proc() failed: %s", strerror(errno));
110        ret = -1;
111    }
112    cap_free(caps);
113
114    return ret;
115}
116