xref: /freebsd/contrib/file/src/seccomp.c (revision 2eb4d8dc723da3cf7d735a3226ae49da4c8c5dbc)
1 /*
2  * Redistribution and use in source and binary forms, with or without
3  * modification, are permitted provided that the following conditions
4  * are met:
5  * 1. Redistributions of source code must retain the above copyright
6  *    notice immediately at the beginning of the file, without modification,
7  *    this list of conditions, and the following disclaimer.
8  * 2. Redistributions in binary form must reproduce the above copyright
9  *    notice, this list of conditions and the following disclaimer in the
10  *    documentation and/or other materials provided with the distribution.
11  *
12  * THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
13  * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
14  * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
15  * ARE DISCLAIMED. IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE FOR
16  * ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
17  * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
18  * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
19  * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
20  * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
21  * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
22  * SUCH DAMAGE.
23  */
24 /*
25  * libseccomp hooks.
26  */
27 #include "file.h"
28 
29 #ifndef	lint
30 FILE_RCSID("@(#)$File: seccomp.c,v 1.15 2020/05/30 23:56:26 christos Exp $")
31 #endif	/* lint */
32 
33 #if HAVE_LIBSECCOMP
34 #include <seccomp.h> /* libseccomp */
35 #include <sys/prctl.h> /* prctl */
36 #include <sys/ioctl.h>
37 #include <sys/socket.h>
38 #include <fcntl.h>
39 #include <stdlib.h>
40 #include <errno.h>
41 
42 #define DENY_RULE(call) \
43     do \
44 	if (seccomp_rule_add (ctx, SCMP_ACT_KILL, SCMP_SYS(call), 0) == -1) \
45 	    goto out; \
46     while (/*CONSTCOND*/0)
47 #define ALLOW_RULE(call) \
48     do \
49 	if (seccomp_rule_add (ctx, SCMP_ACT_ALLOW, SCMP_SYS(call), 0) == -1) \
50 	    goto out; \
51     while (/*CONSTCOND*/0)
52 
53 #define ALLOW_IOCTL_RULE(param) \
54     do \
55 	if (seccomp_rule_add(ctx, SCMP_ACT_ALLOW, SCMP_SYS(ioctl), 1, \
56 	    SCMP_CMP(1, SCMP_CMP_EQ, param)) == -1) \
57 		goto out; \
58     while (/*CONSTCOND*/0)
59 
60 static scmp_filter_ctx ctx;
61 
62 int
63 enable_sandbox_basic(void)
64 {
65 
66 	if (prctl(PR_SET_NO_NEW_PRIVS, 1, 0, 0, 0) == -1)
67 		return -1;
68 
69 	if (prctl(PR_SET_DUMPABLE, 0, 0, 0, 0) == -1)
70 		return -1;
71 
72 	// initialize the filter
73 	ctx = seccomp_init(SCMP_ACT_ALLOW);
74 	if (ctx == NULL)
75 	    return 1;
76 
77 	DENY_RULE(_sysctl);
78 	DENY_RULE(acct);
79 	DENY_RULE(add_key);
80 	DENY_RULE(adjtimex);
81 	DENY_RULE(chroot);
82 	DENY_RULE(clock_adjtime);
83 	DENY_RULE(create_module);
84 	DENY_RULE(delete_module);
85 	DENY_RULE(fanotify_init);
86 	DENY_RULE(finit_module);
87 	DENY_RULE(get_kernel_syms);
88 	DENY_RULE(get_mempolicy);
89 	DENY_RULE(init_module);
90 	DENY_RULE(io_cancel);
91 	DENY_RULE(io_destroy);
92 	DENY_RULE(io_getevents);
93 	DENY_RULE(io_setup);
94 	DENY_RULE(io_submit);
95 	DENY_RULE(ioperm);
96 	DENY_RULE(iopl);
97 	DENY_RULE(ioprio_set);
98 	DENY_RULE(kcmp);
99 #ifdef __NR_kexec_file_load
100 	DENY_RULE(kexec_file_load);
101 #endif
102 	DENY_RULE(kexec_load);
103 	DENY_RULE(keyctl);
104 	DENY_RULE(lookup_dcookie);
105 	DENY_RULE(mbind);
106 	DENY_RULE(nfsservctl);
107 	DENY_RULE(migrate_pages);
108 	DENY_RULE(modify_ldt);
109 	DENY_RULE(mount);
110 	DENY_RULE(move_pages);
111 	DENY_RULE(name_to_handle_at);
112 	DENY_RULE(open_by_handle_at);
113 	DENY_RULE(perf_event_open);
114 	DENY_RULE(pivot_root);
115 	DENY_RULE(process_vm_readv);
116 	DENY_RULE(process_vm_writev);
117 	DENY_RULE(ptrace);
118 	DENY_RULE(reboot);
119 	DENY_RULE(remap_file_pages);
120 	DENY_RULE(request_key);
121 	DENY_RULE(set_mempolicy);
122 	DENY_RULE(swapoff);
123 	DENY_RULE(swapon);
124 	DENY_RULE(sysfs);
125 	DENY_RULE(syslog);
126 	DENY_RULE(tuxcall);
127 	DENY_RULE(umount2);
128 	DENY_RULE(uselib);
129 	DENY_RULE(vmsplice);
130 
131 	// blocking dangerous syscalls that file should not need
132 	DENY_RULE (execve);
133 	DENY_RULE (socket);
134 	// ...
135 
136 
137 	// applying filter...
138 	if (seccomp_load (ctx) == -1)
139 		goto out;
140 	// free ctx after the filter has been loaded into the kernel
141 	seccomp_release(ctx);
142 	return 0;
143 
144 out:
145 	seccomp_release(ctx);
146 	return -1;
147 }
148 
149 
150 int
151 enable_sandbox_full(void)
152 {
153 
154 	// prevent child processes from getting more priv e.g. via setuid,
155 	// capabilities, ...
156 	if (prctl(PR_SET_NO_NEW_PRIVS, 1, 0, 0, 0) == -1)
157 		return -1;
158 
159 	if (prctl(PR_SET_DUMPABLE, 0, 0, 0, 0) == -1)
160 		return -1;
161 
162 	// initialize the filter
163 	ctx = seccomp_init(SCMP_ACT_KILL);
164 	if (ctx == NULL)
165 		return -1;
166 
167 	ALLOW_RULE(access);
168 	ALLOW_RULE(brk);
169 	ALLOW_RULE(close);
170 	ALLOW_RULE(dup2);
171 	ALLOW_RULE(exit);
172 	ALLOW_RULE(exit_group);
173 	ALLOW_RULE(fcntl);
174  	ALLOW_RULE(fcntl64);
175 	ALLOW_RULE(fstat);
176  	ALLOW_RULE(fstat64);
177 #ifdef XZLIBSUPPORT
178 	ALLOW_RULE(futex);
179 #endif
180 	ALLOW_RULE(getdents);
181 #ifdef __NR_getdents64
182 	ALLOW_RULE(getdents64);
183 #endif
184 #ifdef FIONREAD
185 	// called in src/compress.c under sread
186 	ALLOW_IOCTL_RULE(FIONREAD);
187 #endif
188 #ifdef TIOCGWINSZ
189 	// musl libc may call ioctl TIOCGWINSZ on stdout
190 	ALLOW_IOCTL_RULE(TIOCGWINSZ);
191 #endif
192 #ifdef TCGETS
193 	// glibc may call ioctl TCGETS on stdout on physical terminal
194 	ALLOW_IOCTL_RULE(TCGETS);
195 #endif
196 	ALLOW_RULE(lseek);
197  	ALLOW_RULE(_llseek);
198 	ALLOW_RULE(lstat);
199  	ALLOW_RULE(lstat64);
200 	ALLOW_RULE(madvise);
201 	ALLOW_RULE(mmap);
202  	ALLOW_RULE(mmap2);
203 	ALLOW_RULE(mprotect);
204 	ALLOW_RULE(mremap);
205 	ALLOW_RULE(munmap);
206 #ifdef __NR_newfstatat
207 	ALLOW_RULE(newfstatat);
208 #endif
209 	ALLOW_RULE(open);
210 	ALLOW_RULE(openat);
211 	ALLOW_RULE(pread64);
212 	ALLOW_RULE(read);
213 	ALLOW_RULE(readlink);
214 #ifdef __NR_readlinkat
215 	ALLOW_RULE(readlinkat);
216 #endif
217 	ALLOW_RULE(rt_sigaction);
218 	ALLOW_RULE(rt_sigprocmask);
219 	ALLOW_RULE(rt_sigreturn);
220 	ALLOW_RULE(select);
221 	ALLOW_RULE(stat);
222 	ALLOW_RULE(stat64);
223 	ALLOW_RULE(sysinfo);
224 	ALLOW_RULE(umask);	// Used in file_pipe2file()
225 	ALLOW_RULE(getpid);	// Used by glibc in file_pipe2file()
226 	ALLOW_RULE(unlink);
227 	ALLOW_RULE(write);
228 
229 
230 #if 0
231 	// needed by valgrind
232 	ALLOW_RULE(gettid);
233 	ALLOW_RULE(rt_sigtimedwait);
234 #endif
235 
236 #if 0
237 	 /* special restrictions for socket, only allow AF_UNIX/AF_LOCAL */
238 	 if (seccomp_rule_add(ctx, SCMP_ACT_ALLOW, SCMP_SYS(socket), 1,
239 	     SCMP_CMP(0, SCMP_CMP_EQ, AF_UNIX)) == -1)
240 	 	goto out;
241 
242 	 if (seccomp_rule_add(ctx, SCMP_ACT_ALLOW, SCMP_SYS(socket), 1,
243 	     SCMP_CMP(0, SCMP_CMP_EQ, AF_LOCAL)) == -1)
244 	 	goto out;
245 
246 
247 	 /* special restrictions for open, prevent opening files for writing */
248 	 if (seccomp_rule_add(ctx, SCMP_ACT_ALLOW, SCMP_SYS(open), 1,
249 	     SCMP_CMP(1, SCMP_CMP_MASKED_EQ, O_WRONLY | O_RDWR, 0)) == -1)
250 	 	goto out;
251 
252 	 if (seccomp_rule_add(ctx, SCMP_ACT_ERRNO(EACCES), SCMP_SYS(open), 1,
253 	     SCMP_CMP(1, SCMP_CMP_MASKED_EQ, O_WRONLY, O_WRONLY)) == -1)
254 	 	goto out;
255 
256 	 if (seccomp_rule_add(ctx, SCMP_ACT_ERRNO(EACCES), SCMP_SYS(open), 1,
257 	     SCMP_CMP(1, SCMP_CMP_MASKED_EQ, O_RDWR, O_RDWR)) == -1)
258 	 	goto out;
259 
260 
261 	 /* allow stderr */
262 	 if (seccomp_rule_add(ctx, SCMP_ACT_ALLOW, SCMP_SYS(write), 1,
263 	     SCMP_CMP(0, SCMP_CMP_EQ, 2)) == -1)
264 		 goto out;
265 #endif
266 
267 	// applying filter...
268 	if (seccomp_load(ctx) == -1)
269 		goto out;
270 	// free ctx after the filter has been loaded into the kernel
271 	seccomp_release(ctx);
272 	return 0;
273 
274 out:
275 	// something went wrong
276 	seccomp_release(ctx);
277 	return -1;
278 }
279 #endif
280