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 1.25 2022/12/26 18:57:29 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 <termios.h>
39 #include <fcntl.h>
40 #include <stdlib.h>
41 #include <errno.h>
42
43 #define DENY_RULE(call) \
44 do \
45 if (seccomp_rule_add (ctx, SCMP_ACT_KILL, SCMP_SYS(call), 0) == -1) \
46 goto out; \
47 while (/*CONSTCOND*/0)
48 #define ALLOW_RULE(call) \
49 do \
50 if (seccomp_rule_add (ctx, SCMP_ACT_ALLOW, SCMP_SYS(call), 0) == -1) \
51 goto out; \
52 while (/*CONSTCOND*/0)
53
54 #define ALLOW_IOCTL_RULE(param) \
55 do \
56 if (seccomp_rule_add(ctx, SCMP_ACT_ALLOW, SCMP_SYS(ioctl), 1, \
57 SCMP_CMP(1, SCMP_CMP_EQ, (scmp_datum_t)param, \
58 (scmp_datum_t)0)) == -1) \
59 goto out; \
60 while (/*CONSTCOND*/0)
61
62 static scmp_filter_ctx ctx;
63
64 int
enable_sandbox_basic(void)65 enable_sandbox_basic(void)
66 {
67
68 if (prctl(PR_SET_NO_NEW_PRIVS, 1, 0, 0, 0) == -1)
69 return -1;
70
71 if (prctl(PR_SET_DUMPABLE, 0, 0, 0, 0) == -1)
72 return -1;
73
74 // initialize the filter
75 ctx = seccomp_init(SCMP_ACT_ALLOW);
76 if (ctx == NULL)
77 return 1;
78
79 DENY_RULE(_sysctl);
80 DENY_RULE(acct);
81 DENY_RULE(add_key);
82 DENY_RULE(adjtimex);
83 DENY_RULE(chroot);
84 DENY_RULE(clock_adjtime);
85 DENY_RULE(create_module);
86 DENY_RULE(delete_module);
87 DENY_RULE(fanotify_init);
88 DENY_RULE(finit_module);
89 DENY_RULE(get_kernel_syms);
90 DENY_RULE(get_mempolicy);
91 DENY_RULE(init_module);
92 DENY_RULE(io_cancel);
93 DENY_RULE(io_destroy);
94 DENY_RULE(io_getevents);
95 DENY_RULE(io_setup);
96 DENY_RULE(io_submit);
97 DENY_RULE(ioperm);
98 DENY_RULE(iopl);
99 DENY_RULE(ioprio_set);
100 DENY_RULE(kcmp);
101 #ifdef __NR_kexec_file_load
102 DENY_RULE(kexec_file_load);
103 #endif
104 DENY_RULE(kexec_load);
105 DENY_RULE(keyctl);
106 DENY_RULE(lookup_dcookie);
107 DENY_RULE(mbind);
108 DENY_RULE(nfsservctl);
109 DENY_RULE(migrate_pages);
110 DENY_RULE(modify_ldt);
111 DENY_RULE(mount);
112 DENY_RULE(move_pages);
113 DENY_RULE(name_to_handle_at);
114 DENY_RULE(open_by_handle_at);
115 DENY_RULE(perf_event_open);
116 DENY_RULE(pivot_root);
117 DENY_RULE(process_vm_readv);
118 DENY_RULE(process_vm_writev);
119 DENY_RULE(ptrace);
120 DENY_RULE(reboot);
121 DENY_RULE(remap_file_pages);
122 DENY_RULE(request_key);
123 DENY_RULE(set_mempolicy);
124 DENY_RULE(swapoff);
125 DENY_RULE(swapon);
126 DENY_RULE(sysfs);
127 DENY_RULE(syslog);
128 DENY_RULE(tuxcall);
129 DENY_RULE(umount2);
130 DENY_RULE(uselib);
131 DENY_RULE(vmsplice);
132
133 // blocking dangerous syscalls that file should not need
134 DENY_RULE (execve);
135 DENY_RULE (socket);
136 // ...
137
138
139 // applying filter...
140 if (seccomp_load (ctx) == -1)
141 goto out;
142 // free ctx after the filter has been loaded into the kernel
143 seccomp_release(ctx);
144 return 0;
145
146 out:
147 seccomp_release(ctx);
148 return -1;
149 }
150
151
152 int
enable_sandbox_full(void)153 enable_sandbox_full(void)
154 {
155
156 // prevent child processes from getting more priv e.g. via setuid,
157 // capabilities, ...
158 if (prctl(PR_SET_NO_NEW_PRIVS, 1, 0, 0, 0) == -1)
159 return -1;
160
161 if (prctl(PR_SET_DUMPABLE, 0, 0, 0, 0) == -1)
162 return -1;
163
164 // initialize the filter
165 ctx = seccomp_init(SCMP_ACT_KILL);
166 if (ctx == NULL)
167 return -1;
168
169 ALLOW_RULE(access);
170 ALLOW_RULE(brk);
171 ALLOW_RULE(close);
172 ALLOW_RULE(dup2);
173 ALLOW_RULE(exit);
174 ALLOW_RULE(exit_group);
175 #ifdef __NR_faccessat
176 ALLOW_RULE(faccessat);
177 #endif
178 ALLOW_RULE(fcntl);
179 ALLOW_RULE(fcntl64);
180 #ifdef __NR_fstat
181 ALLOW_RULE(fstat);
182 #endif
183 ALLOW_RULE(fstat64);
184 #ifdef __NR_fstatat64
185 ALLOW_RULE(fstatat64);
186 #endif
187 ALLOW_RULE(futex);
188 ALLOW_RULE(getdents);
189 #ifdef __NR_getdents64
190 ALLOW_RULE(getdents64);
191 #endif
192 #ifdef FIONREAD
193 // called in src/compress.c under sread
194 ALLOW_IOCTL_RULE(FIONREAD);
195 #endif
196 #ifdef TIOCGWINSZ
197 // musl libc may call ioctl TIOCGWINSZ on stdout
198 ALLOW_IOCTL_RULE(TIOCGWINSZ);
199 #endif
200 #ifdef TCGETS
201 // glibc may call ioctl TCGETS on stdout on physical terminal
202 ALLOW_IOCTL_RULE(TCGETS);
203 #endif
204 ALLOW_RULE(lseek);
205 ALLOW_RULE(_llseek);
206 ALLOW_RULE(lstat);
207 ALLOW_RULE(lstat64);
208 ALLOW_RULE(madvise);
209 ALLOW_RULE(mmap);
210 ALLOW_RULE(mmap2);
211 ALLOW_RULE(mprotect);
212 ALLOW_RULE(mremap);
213 ALLOW_RULE(munmap);
214 #ifdef __NR_newfstatat
215 ALLOW_RULE(newfstatat);
216 #endif
217 ALLOW_RULE(open);
218 ALLOW_RULE(openat);
219 ALLOW_RULE(pread64);
220 ALLOW_RULE(read);
221 ALLOW_RULE(readlink);
222 #ifdef __NR_readlinkat
223 ALLOW_RULE(readlinkat);
224 #endif
225 ALLOW_RULE(rt_sigaction);
226 ALLOW_RULE(rt_sigprocmask);
227 ALLOW_RULE(rt_sigreturn);
228 ALLOW_RULE(select);
229 ALLOW_RULE(stat);
230 ALLOW_RULE(statx);
231 ALLOW_RULE(stat64);
232 ALLOW_RULE(sysinfo);
233 ALLOW_RULE(umask); // Used in file_pipe2file()
234 ALLOW_RULE(getpid); // Used by glibc in file_pipe2file()
235 ALLOW_RULE(unlink);
236 ALLOW_RULE(utimes);
237 ALLOW_RULE(write);
238 ALLOW_RULE(writev);
239
240
241 #if 0
242 // needed by valgrind
243 ALLOW_RULE(gettid);
244 ALLOW_RULE(rt_sigtimedwait);
245 #endif
246
247 #if 0
248 /* special restrictions for socket, only allow AF_UNIX/AF_LOCAL */
249 if (seccomp_rule_add(ctx, SCMP_ACT_ALLOW, SCMP_SYS(socket), 1,
250 SCMP_CMP(0, SCMP_CMP_EQ, AF_UNIX)) == -1)
251 goto out;
252
253 if (seccomp_rule_add(ctx, SCMP_ACT_ALLOW, SCMP_SYS(socket), 1,
254 SCMP_CMP(0, SCMP_CMP_EQ, AF_LOCAL)) == -1)
255 goto out;
256
257
258 /* special restrictions for open, prevent opening files for writing */
259 if (seccomp_rule_add(ctx, SCMP_ACT_ALLOW, SCMP_SYS(open), 1,
260 SCMP_CMP(1, SCMP_CMP_MASKED_EQ, O_WRONLY | O_RDWR, 0)) == -1)
261 goto out;
262
263 if (seccomp_rule_add(ctx, SCMP_ACT_ERRNO(EACCES), SCMP_SYS(open), 1,
264 SCMP_CMP(1, SCMP_CMP_MASKED_EQ, O_WRONLY, O_WRONLY)) == -1)
265 goto out;
266
267 if (seccomp_rule_add(ctx, SCMP_ACT_ERRNO(EACCES), SCMP_SYS(open), 1,
268 SCMP_CMP(1, SCMP_CMP_MASKED_EQ, O_RDWR, O_RDWR)) == -1)
269 goto out;
270
271
272 /* allow stderr */
273 if (seccomp_rule_add(ctx, SCMP_ACT_ALLOW, SCMP_SYS(write), 1,
274 SCMP_CMP(0, SCMP_CMP_EQ, 2)) == -1)
275 goto out;
276 #endif
277
278 // applying filter...
279 if (seccomp_load(ctx) == -1)
280 goto out;
281 // free ctx after the filter has been loaded into the kernel
282 seccomp_release(ctx);
283 return 0;
284
285 out:
286 // something went wrong
287 seccomp_release(ctx);
288 return -1;
289 }
290 #endif
291