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 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 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