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 1.29 2024/09/29 16:49:25 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(void)65 enable_sandbox(void)
66 {
67
68 // prevent child processes from getting more priv e.g. via setuid,
69 // capabilities, ...
70 if (prctl(PR_SET_NO_NEW_PRIVS, 1, 0, 0, 0) == -1)
71 return -1;
72
73 #if 0
74 if (prctl(PR_SET_DUMPABLE, 0, 0, 0, 0) == -1)
75 return -1;
76 #endif
77
78 // initialize the filter
79 ctx = seccomp_init(SCMP_ACT_KILL);
80 if (ctx == NULL)
81 return -1;
82
83 ALLOW_RULE(access);
84 ALLOW_RULE(brk);
85 ALLOW_RULE(close);
86 ALLOW_RULE(dup2);
87 ALLOW_RULE(exit);
88 ALLOW_RULE(exit_group);
89 #ifdef __NR_faccessat
90 ALLOW_RULE(faccessat);
91 #endif
92 ALLOW_RULE(fcntl);
93 ALLOW_RULE(fcntl64);
94 #ifdef __NR_fstat
95 ALLOW_RULE(fstat);
96 #endif
97 ALLOW_RULE(fstat64);
98 #ifdef __NR_fstatat64
99 ALLOW_RULE(fstatat64);
100 #endif
101 ALLOW_RULE(futex);
102 ALLOW_RULE(getdents);
103 #ifdef __NR_getdents64
104 ALLOW_RULE(getdents64);
105 #endif
106 #ifdef FIONREAD
107 // called in src/compress.c under sread
108 ALLOW_IOCTL_RULE(FIONREAD);
109 #endif
110 #ifdef TIOCGWINSZ
111 // musl libc may call ioctl TIOCGWINSZ on stdout
112 ALLOW_IOCTL_RULE(TIOCGWINSZ);
113 #endif
114 #ifdef TCGETS
115 // glibc may call ioctl TCGETS on stdout on physical terminal
116 ALLOW_IOCTL_RULE(TCGETS);
117 #endif
118 ALLOW_RULE(lseek);
119 ALLOW_RULE(_llseek);
120 ALLOW_RULE(lstat);
121 ALLOW_RULE(lstat64);
122 ALLOW_RULE(madvise);
123 ALLOW_RULE(mmap);
124 ALLOW_RULE(mmap2);
125 ALLOW_RULE(mprotect);
126 ALLOW_RULE(mremap);
127 ALLOW_RULE(munmap);
128 #ifdef __NR_newfstatat
129 ALLOW_RULE(newfstatat);
130 #endif
131 ALLOW_RULE(open);
132 ALLOW_RULE(openat);
133 ALLOW_RULE(pread64);
134 ALLOW_RULE(read);
135 ALLOW_RULE(readlink);
136 #ifdef __NR_readlinkat
137 ALLOW_RULE(readlinkat);
138 #endif
139 ALLOW_RULE(rt_sigaction);
140 ALLOW_RULE(rt_sigprocmask);
141 ALLOW_RULE(rt_sigreturn);
142 ALLOW_RULE(select);
143 ALLOW_RULE(stat);
144 ALLOW_RULE(statx);
145 ALLOW_RULE(stat64);
146 ALLOW_RULE(sysinfo);
147 ALLOW_RULE(umask); // Used in file_pipe2file()
148 ALLOW_RULE(getpid); // Used by glibc in file_pipe2file()
149 ALLOW_RULE(getrandom); // Used by glibc in file_pipe2file()
150 ALLOW_RULE(unlink);
151 ALLOW_RULE(utimes);
152 ALLOW_RULE(write);
153 ALLOW_RULE(writev);
154
155
156 #if 0
157 // needed by valgrind
158 ALLOW_RULE(gettid);
159 ALLOW_RULE(rt_sigtimedwait);
160 #endif
161
162 #if 0
163 /* special restrictions for socket, only allow AF_UNIX/AF_LOCAL */
164 if (seccomp_rule_add(ctx, SCMP_ACT_ALLOW, SCMP_SYS(socket), 1,
165 SCMP_CMP(0, SCMP_CMP_EQ, AF_UNIX)) == -1)
166 goto out;
167
168 if (seccomp_rule_add(ctx, SCMP_ACT_ALLOW, SCMP_SYS(socket), 1,
169 SCMP_CMP(0, SCMP_CMP_EQ, AF_LOCAL)) == -1)
170 goto out;
171
172
173 /* special restrictions for open, prevent opening files for writing */
174 if (seccomp_rule_add(ctx, SCMP_ACT_ALLOW, SCMP_SYS(open), 1,
175 SCMP_CMP(1, SCMP_CMP_MASKED_EQ, O_WRONLY | O_RDWR, 0)) == -1)
176 goto out;
177
178 if (seccomp_rule_add(ctx, SCMP_ACT_ERRNO(EACCES), SCMP_SYS(open), 1,
179 SCMP_CMP(1, SCMP_CMP_MASKED_EQ, O_WRONLY, O_WRONLY)) == -1)
180 goto out;
181
182 if (seccomp_rule_add(ctx, SCMP_ACT_ERRNO(EACCES), SCMP_SYS(open), 1,
183 SCMP_CMP(1, SCMP_CMP_MASKED_EQ, O_RDWR, O_RDWR)) == -1)
184 goto out;
185
186
187 /* allow stderr */
188 if (seccomp_rule_add(ctx, SCMP_ACT_ALLOW, SCMP_SYS(write), 1,
189 SCMP_CMP(0, SCMP_CMP_EQ, 2)) == -1)
190 goto out;
191 #endif
192
193 #if defined(PR_SET_VMA) && defined(PR_SET_VMA_ANON_NAME)
194 /* allow glibc to name malloc areas */
195 if (seccomp_rule_add(ctx, SCMP_ACT_ALLOW, SCMP_SYS(prctl), 2,
196 SCMP_CMP32(0, SCMP_CMP_EQ, PR_SET_VMA),
197 SCMP_CMP64(1, SCMP_CMP_EQ, PR_SET_VMA_ANON_NAME)) == -1)
198 goto out;
199 #endif
200
201 // applying filter...
202 if (seccomp_load(ctx) == -1)
203 goto out;
204 // free ctx after the filter has been loaded into the kernel
205 seccomp_release(ctx);
206 return 0;
207
208 out:
209 // something went wrong
210 seccomp_release(ctx);
211 return -1;
212 }
213 #endif
214