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
avahi_caps_reduce(void)35 int 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
avahi_caps_reduce2(void)66 int 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
avahi_caps_drop_all(void)98 int 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