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
enable_sandbox_basic(void)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
enable_sandbox_full(void)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