xref: /freebsd/contrib/file/src/seccomp.c (revision ae316d1d1cffd71ab7751f94e10118777a88e027)
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