xref: /freebsd/crypto/openssh/sandbox-capsicum.c (revision f39bffc62c1395bde25d152c7f68fdf7cbaab414)
1 /*
2  * Copyright (c) 2011 Dag-Erling Smorgrav
3  *
4  * Permission to use, copy, modify, and distribute this software for any
5  * purpose with or without fee is hereby granted, provided that the above
6  * copyright notice and this permission notice appear in all copies.
7  *
8  * THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
9  * WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
10  * MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
11  * ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
12  * WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
13  * ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
14  * OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
15  */
16 
17 #include "includes.h"
18 __RCSID("$FreeBSD$");
19 
20 #ifdef SANDBOX_CAPSICUM
21 
22 #include <sys/types.h>
23 #include <sys/param.h>
24 #include <sys/time.h>
25 #include <sys/resource.h>
26 #include <sys/capsicum.h>
27 
28 #include <errno.h>
29 #include <stdarg.h>
30 #include <stdio.h>
31 #include <stdlib.h>
32 #include <string.h>
33 #include <unistd.h>
34 
35 #include "log.h"
36 #include "monitor.h"
37 #include "ssh-sandbox.h"
38 #include "xmalloc.h"
39 
40 /*
41  * Capsicum sandbox that sets zero nfiles, nprocs and filesize rlimits,
42  * limits rights on stdout, stdin, stderr, monitor and switches to
43  * capability mode.
44  */
45 
46 struct ssh_sandbox {
47 	struct monitor *monitor;
48 	pid_t child_pid;
49 };
50 
51 struct ssh_sandbox *
52 ssh_sandbox_init(struct monitor *monitor)
53 {
54 	struct ssh_sandbox *box;
55 
56 	/*
57 	 * Strictly, we don't need to maintain any state here but we need
58 	 * to return non-NULL to satisfy the API.
59 	 */
60 	debug3("%s: preparing capsicum sandbox", __func__);
61 	box = xcalloc(1, sizeof(*box));
62 	box->monitor = monitor;
63 	box->child_pid = 0;
64 
65 	return box;
66 }
67 
68 void
69 ssh_sandbox_child(struct ssh_sandbox *box)
70 {
71 	struct rlimit rl_zero;
72 	cap_rights_t rights;
73 
74 	rl_zero.rlim_cur = rl_zero.rlim_max = 0;
75 
76 	if (setrlimit(RLIMIT_FSIZE, &rl_zero) == -1)
77 		fatal("%s: setrlimit(RLIMIT_FSIZE, { 0, 0 }): %s",
78 			__func__, strerror(errno));
79 #ifndef SANDBOX_SKIP_RLIMIT_NOFILE
80 	if (setrlimit(RLIMIT_NOFILE, &rl_zero) == -1)
81 		fatal("%s: setrlimit(RLIMIT_NOFILE, { 0, 0 }): %s",
82 			__func__, strerror(errno));
83 #endif
84 	if (setrlimit(RLIMIT_NPROC, &rl_zero) == -1)
85 		fatal("%s: setrlimit(RLIMIT_NPROC, { 0, 0 }): %s",
86 			__func__, strerror(errno));
87 
88 	cap_rights_init(&rights);
89 
90 	if (cap_rights_limit(STDIN_FILENO, &rights) < 0 && errno != ENOSYS)
91 		fatal("can't limit stdin: %m");
92 	if (cap_rights_limit(STDOUT_FILENO, &rights) < 0 && errno != ENOSYS)
93 		fatal("can't limit stdout: %m");
94 	if (cap_rights_limit(STDERR_FILENO, &rights) < 0 && errno != ENOSYS)
95 		fatal("can't limit stderr: %m");
96 
97 	cap_rights_init(&rights, CAP_READ, CAP_WRITE);
98 	if (cap_rights_limit(box->monitor->m_recvfd, &rights) < 0 &&
99 	    errno != ENOSYS)
100 		fatal("%s: failed to limit the network socket", __func__);
101 	cap_rights_init(&rights, CAP_WRITE);
102 	if (cap_rights_limit(box->monitor->m_log_sendfd, &rights) < 0 &&
103 	    errno != ENOSYS)
104 		fatal("%s: failed to limit the logging socket", __func__);
105 	if (cap_enter() < 0 && errno != ENOSYS)
106 		fatal("%s: failed to enter capability mode", __func__);
107 
108 }
109 
110 void
111 ssh_sandbox_parent_finish(struct ssh_sandbox *box)
112 {
113 	free(box);
114 	debug3("%s: finished", __func__);
115 }
116 
117 void
118 ssh_sandbox_parent_preauth(struct ssh_sandbox *box, pid_t child_pid)
119 {
120 	box->child_pid = child_pid;
121 }
122 
123 #endif /* SANDBOX_CAPSICUM */
124