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 1.36 2026/02/06 14:04:20 christos Exp $")
31 #endif /* lint */
32
33 #if HAVE_LIBSECCOMP
34 #include <seccomp.h> /* libseccomp */
35 #include <sys/prctl.h> /* prctl */
36 #include <sys/socket.h>
37 // See: https://sourceware.org/bugzilla/show_bug.cgi?id=32806
38 #include <asm/termbits.h>
39 #include <sys/ioctl.h>
40 #include <fcntl.h>
41 #include <stdlib.h>
42 #include <errno.h>
43
44 #define DENY_RULE(call) \
45 do \
46 if (seccomp_rule_add (ctx, SCMP_ACT_KILL, SCMP_SYS(call), 0) == -1) \
47 goto out; \
48 while (/*CONSTCOND*/0)
49 #define ALLOW_RULE(call) \
50 do \
51 if (seccomp_rule_add (ctx, SCMP_ACT_ALLOW, SCMP_SYS(call), 0) == -1) \
52 goto out; \
53 while (/*CONSTCOND*/0)
54
55 #define ALLOW_IOCTL_RULE(param) \
56 do \
57 if (seccomp_rule_add(ctx, SCMP_ACT_ALLOW, SCMP_SYS(ioctl), 1, \
58 SCMP_CMP(1, SCMP_CMP_EQ, (scmp_datum_t)param, \
59 (scmp_datum_t)0)) == -1) \
60 goto out; \
61 while (/*CONSTCOND*/0)
62
63 static scmp_filter_ctx ctx;
64
65 int
enable_sandbox(void)66 enable_sandbox(void)
67 {
68
69 // prevent child processes from getting more priv e.g. via setuid,
70 // capabilities, ...
71 if (prctl(PR_SET_NO_NEW_PRIVS, 1, 0, 0, 0) == -1)
72 return -1;
73
74 #if 0
75 if (prctl(PR_SET_DUMPABLE, 0, 0, 0, 0) == -1)
76 return -1;
77 #endif
78
79 // initialize the filter
80 ctx = seccomp_init(SCMP_ACT_KILL);
81 if (ctx == NULL)
82 return -1;
83
84 ALLOW_RULE(access);
85 ALLOW_RULE(brk);
86 ALLOW_RULE(close);
87 ALLOW_RULE(dup2);
88 ALLOW_RULE(exit);
89 ALLOW_RULE(exit_group);
90 #ifdef __NR_faccessat
91 ALLOW_RULE(faccessat);
92 #endif
93 ALLOW_RULE(fcntl);
94 ALLOW_RULE(fcntl64);
95 #ifdef __NR_fstat
96 ALLOW_RULE(fstat);
97 #endif
98 ALLOW_RULE(fstat64);
99 #ifdef __NR_fstatat64
100 ALLOW_RULE(fstatat64);
101 #endif
102 ALLOW_RULE(futex);
103 ALLOW_RULE(getdents);
104 #ifdef __NR_getdents64
105 ALLOW_RULE(getdents64);
106 #endif
107 ALLOW_RULE(getpid); // Used by glibc in file_pipe2file()
108 ALLOW_RULE(getrandom); // Used by glibc in file_pipe2file()
109 #ifdef __NR_getcwd
110 ALLOW_RULE(getcwd); // GCONV_PATH=
111 #endif
112 #ifdef FIONREAD
113 // called in src/compress.c under sread
114 ALLOW_IOCTL_RULE(FIONREAD);
115 #endif
116 #ifdef TIOCGWINSZ
117 // musl libc may call ioctl TIOCGWINSZ on stdout
118 ALLOW_IOCTL_RULE(TIOCGWINSZ);
119 #endif
120 #ifdef TCGETS
121 // glibc may call ioctl TCGETS on stdout on physical terminal
122 ALLOW_IOCTL_RULE(TCGETS);
123 #endif
124 #ifdef TCGETS2
125 // glibc may call ioctl TCGETS2 on stdout on physical terminal
126 ALLOW_IOCTL_RULE(TCGETS2);
127 #endif
128 ALLOW_RULE(lseek);
129 ALLOW_RULE(_llseek);
130 ALLOW_RULE(lstat);
131 ALLOW_RULE(lstat64);
132 ALLOW_RULE(madvise);
133 ALLOW_RULE(mmap);
134 ALLOW_RULE(mmap2);
135 ALLOW_RULE(mprotect);
136 ALLOW_RULE(mremap);
137 ALLOW_RULE(munmap);
138 #ifdef __NR_newfstatat
139 ALLOW_RULE(newfstatat);
140 #endif
141 ALLOW_RULE(open);
142 ALLOW_RULE(openat);
143 ALLOW_RULE(pread64);
144 ALLOW_RULE(read);
145 ALLOW_RULE(readlink);
146 #ifdef __NR_readlinkat
147 ALLOW_RULE(readlinkat);
148 #endif
149 ALLOW_RULE(rseq); // Used by glibc to randomize malloc
150 ALLOW_RULE(rt_sigaction);
151 ALLOW_RULE(rt_sigprocmask);
152 ALLOW_RULE(rt_sigreturn);
153 ALLOW_RULE(select);
154 ALLOW_RULE(stat);
155 ALLOW_RULE(statx);
156 ALLOW_RULE(stat64);
157 ALLOW_RULE(sysinfo);
158 ALLOW_RULE(umask); // Used in file_pipe2file()
159 ALLOW_RULE(unlink);
160 ALLOW_RULE(utimes);
161 ALLOW_RULE(write);
162 ALLOW_RULE(writev);
163
164
165 #if 0
166 // needed by valgrind
167 ALLOW_RULE(gettid);
168 ALLOW_RULE(rt_sigtimedwait);
169 #endif
170
171 #if 0
172 /* special restrictions for socket, only allow AF_UNIX/AF_LOCAL */
173 if (seccomp_rule_add(ctx, SCMP_ACT_ALLOW, SCMP_SYS(socket), 1,
174 SCMP_CMP(0, SCMP_CMP_EQ, AF_UNIX)) == -1)
175 goto out;
176
177 if (seccomp_rule_add(ctx, SCMP_ACT_ALLOW, SCMP_SYS(socket), 1,
178 SCMP_CMP(0, SCMP_CMP_EQ, AF_LOCAL)) == -1)
179 goto out;
180
181
182 /* special restrictions for open, prevent opening files for writing */
183 if (seccomp_rule_add(ctx, SCMP_ACT_ALLOW, SCMP_SYS(open), 1,
184 SCMP_CMP(1, SCMP_CMP_MASKED_EQ, O_WRONLY | O_RDWR, 0)) == -1)
185 goto out;
186
187 if (seccomp_rule_add(ctx, SCMP_ACT_ERRNO(EACCES), SCMP_SYS(open), 1,
188 SCMP_CMP(1, SCMP_CMP_MASKED_EQ, O_WRONLY, O_WRONLY)) == -1)
189 goto out;
190
191 if (seccomp_rule_add(ctx, SCMP_ACT_ERRNO(EACCES), SCMP_SYS(open), 1,
192 SCMP_CMP(1, SCMP_CMP_MASKED_EQ, O_RDWR, O_RDWR)) == -1)
193 goto out;
194
195
196 /* allow stderr */
197 if (seccomp_rule_add(ctx, SCMP_ACT_ALLOW, SCMP_SYS(write), 1,
198 SCMP_CMP(0, SCMP_CMP_EQ, 2)) == -1)
199 goto out;
200 #endif
201
202 #if defined(PR_SET_VMA) && defined(PR_SET_VMA_ANON_NAME)
203 /* allow glibc to name malloc areas */
204 if (seccomp_rule_add(ctx, SCMP_ACT_ALLOW, SCMP_SYS(prctl), 2,
205 SCMP_CMP32(0, SCMP_CMP_EQ, PR_SET_VMA),
206 SCMP_CMP64(1, SCMP_CMP_EQ, PR_SET_VMA_ANON_NAME)) == -1)
207 goto out;
208 #endif
209
210 // applying filter...
211 if (seccomp_load(ctx) == -1)
212 goto out;
213 // free ctx after the filter has been loaded into the kernel
214 seccomp_release(ctx);
215 return 0;
216
217 out:
218 // something went wrong
219 seccomp_release(ctx);
220 return -1;
221 }
222 #endif
223