crypto/openssh/sandbox-seccomp-filter.c

   1 /*
   2  * Copyright (c) 2012 Will Drewry <wad@dataspill.org>
   3  * Copyright (c) 2015,2017,2019,2020,2023 Damien Miller <djm@mindrot.org>
   4  *
   5  * Permission to use, copy, modify, and distribute this software for any
   6  * purpose with or without fee is hereby granted, provided that the above
   7  * copyright notice and this permission notice appear in all copies.
   8  *
   9  * THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
  10  * WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
  11  * MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
  12  * ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
  13  * WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
  14  * ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
  15  * OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
  16  */
  17
  18 /*
  19  * Uncomment the SANDBOX_SECCOMP_FILTER_DEBUG macro below to help diagnose
  20  * filter breakage during development. *Do not* use this in production,
  21  * as it relies on making library calls that are unsafe in signal context.
  22  *
  23  * Instead, live systems the auditctl(8) may be used to monitor failures.
  24  * E.g.
  25  *   auditctl -a task,always -F uid=<privsep uid>
  26  */
  27 /* #define SANDBOX_SECCOMP_FILTER_DEBUG 1 */
  28
  29 #if 0
  30 /*
  31  * For older toolchains, it may be necessary to use the kernel
  32  * headers directly.
  33  */
  34 #ifdef SANDBOX_SECCOMP_FILTER_DEBUG
  35 # include <asm/siginfo.h>
  36 # define __have_siginfo_t 1
  37 # define __have_sigval_t 1
  38 # define __have_sigevent_t 1
  39 #endif /* SANDBOX_SECCOMP_FILTER_DEBUG */
  40 #endif
  41
  42 #include "includes.h"
  43
  44 #ifdef SANDBOX_SECCOMP_FILTER
  45
  46 #include <sys/types.h>
  47 #include <sys/resource.h>
  48 #include <sys/prctl.h>
  49 #include <sys/mman.h>
  50 #include <sys/syscall.h>
  51
  52 #include <linux/futex.h>
  53 #include <linux/net.h>
  54 #include <linux/audit.h>
  55 #include <linux/filter.h>
  56 #include <linux/seccomp.h>
  57 #include <elf.h>
  58
  59 #include <asm/unistd.h>
  60 #ifdef __s390__
  61 #include <asm/zcrypt.h>
  62 #endif
  63
  64 #include <errno.h>
  65 #include <signal.h>
  66 #include <stdarg.h>
  67 #include <stddef.h>  /* for offsetof */
  68 #include <stdio.h>
  69 #include <stdlib.h>
  70 #include <string.h>
  71 #include <unistd.h>
  72
  73 #include "log.h"
  74 #include "ssh-sandbox.h"
  75 #include "xmalloc.h"
  76
  77 /* Linux seccomp_filter sandbox */
  78 #define SECCOMP_FILTER_FAIL SECCOMP_RET_KILL
  79
  80 /* Use a signal handler to emit violations when debugging */
  81 #ifdef SANDBOX_SECCOMP_FILTER_DEBUG
  82 # undef SECCOMP_FILTER_FAIL
  83 # define SECCOMP_FILTER_FAIL SECCOMP_RET_TRAP
  84 #endif /* SANDBOX_SECCOMP_FILTER_DEBUG */
  85
  86 #if __BYTE_ORDER == __LITTLE_ENDIAN
  87 # define ARG_LO_OFFSET  0
  88 # define ARG_HI_OFFSET  sizeof(uint32_t)
  89 #elif __BYTE_ORDER == __BIG_ENDIAN
  90 # define ARG_LO_OFFSET  sizeof(uint32_t)
  91 # define ARG_HI_OFFSET  0
  92 #else
  93 #error "Unknown endianness"
  94 #endif
  95
  96 /* Simple helpers to avoid manual errors (but larger BPF programs). */
  97 #define SC_DENY(_nr, _errno) \
  98         BPF_JUMP(BPF_JMP+BPF_JEQ+BPF_K, (_nr), 0, 1), \
  99         BPF_STMT(BPF_RET+BPF_K, SECCOMP_RET_ERRNO|(_errno))
 100 #define SC_ALLOW(_nr) \
 101         BPF_JUMP(BPF_JMP+BPF_JEQ+BPF_K, (_nr), 0, 1), \
 102         BPF_STMT(BPF_RET+BPF_K, SECCOMP_RET_ALLOW)
 103 #define SC_ALLOW_ARG(_nr, _arg_nr, _arg_val) \
 104         BPF_JUMP(BPF_JMP+BPF_JEQ+BPF_K, (_nr), 0, 6), \
 105         /* load and test syscall argument, low word */ \
 106         BPF_STMT(BPF_LD+BPF_W+BPF_ABS, \
 107             offsetof(struct seccomp_data, args[(_arg_nr)]) + ARG_LO_OFFSET), \
 108         BPF_JUMP(BPF_JMP+BPF_JEQ+BPF_K, \
 109             ((_arg_val) & 0xFFFFFFFF), 0, 3), \
 110         /* load and test syscall argument, high word */ \
 111         BPF_STMT(BPF_LD+BPF_W+BPF_ABS, \
 112             offsetof(struct seccomp_data, args[(_arg_nr)]) + ARG_HI_OFFSET), \
 113         BPF_JUMP(BPF_JMP+BPF_JEQ+BPF_K, \
 114             (((uint32_t)((uint64_t)(_arg_val) >> 32)) & 0xFFFFFFFF), 0, 1), \
 115         BPF_STMT(BPF_RET+BPF_K, SECCOMP_RET_ALLOW), \
 116         /* reload syscall number; all rules expect it in accumulator */ \
 117         BPF_STMT(BPF_LD+BPF_W+BPF_ABS, \
 118                 offsetof(struct seccomp_data, nr))
 119 /* Allow if syscall argument contains only values in mask */
 120 #define SC_ALLOW_ARG_MASK(_nr, _arg_nr, _arg_mask) \
 121         BPF_JUMP(BPF_JMP+BPF_JEQ+BPF_K, (_nr), 0, 8), \
 122         /* load, mask and test syscall argument, low word */ \
 123         BPF_STMT(BPF_LD+BPF_W+BPF_ABS, \
 124             offsetof(struct seccomp_data, args[(_arg_nr)]) + ARG_LO_OFFSET), \
 125         BPF_STMT(BPF_ALU+BPF_AND+BPF_K, ~((_arg_mask) & 0xFFFFFFFF)), \
 126         BPF_JUMP(BPF_JMP+BPF_JEQ+BPF_K, 0, 0, 4), \
 127         /* load, mask and test syscall argument, high word */ \
 128         BPF_STMT(BPF_LD+BPF_W+BPF_ABS, \
 129             offsetof(struct seccomp_data, args[(_arg_nr)]) + ARG_HI_OFFSET), \
 130         BPF_STMT(BPF_ALU+BPF_AND+BPF_K, \
 131             ~(((uint32_t)((uint64_t)(_arg_mask) >> 32)) & 0xFFFFFFFF)), \
 132         BPF_JUMP(BPF_JMP+BPF_JEQ+BPF_K, 0, 0, 1), \
 133         BPF_STMT(BPF_RET+BPF_K, SECCOMP_RET_ALLOW), \
 134         /* reload syscall number; all rules expect it in accumulator */ \
 135         BPF_STMT(BPF_LD+BPF_W+BPF_ABS, \
 136                 offsetof(struct seccomp_data, nr))
 137 /* Deny unless syscall argument contains only values in mask */
 138 #define SC_DENY_UNLESS_ARG_MASK(_nr, _arg_nr, _arg_mask, _errno) \
 139         BPF_JUMP(BPF_JMP+BPF_JEQ+BPF_K, (_nr), 0, 8), \
 140         /* load, mask and test syscall argument, low word */ \
 141         BPF_STMT(BPF_LD+BPF_W+BPF_ABS, \
 142             offsetof(struct seccomp_data, args[(_arg_nr)]) + ARG_LO_OFFSET), \
 143         BPF_STMT(BPF_ALU+BPF_AND+BPF_K, ~((_arg_mask) & 0xFFFFFFFF)), \
 144         BPF_JUMP(BPF_JMP+BPF_JEQ+BPF_K, 0, 0, 3), \
 145         /* load, mask and test syscall argument, high word */ \
 146         BPF_STMT(BPF_LD+BPF_W+BPF_ABS, \
 147             offsetof(struct seccomp_data, args[(_arg_nr)]) + ARG_HI_OFFSET), \
 148         BPF_STMT(BPF_ALU+BPF_AND+BPF_K, \
 149             ~(((uint32_t)((uint64_t)(_arg_mask) >> 32)) & 0xFFFFFFFF)), \
 150         BPF_JUMP(BPF_JMP+BPF_JEQ+BPF_K, 0, 1, 0), \
 151         BPF_STMT(BPF_RET+BPF_K, SECCOMP_RET_ERRNO|(_errno)), \
 152         /* reload syscall number; all rules expect it in accumulator */ \
 153         BPF_STMT(BPF_LD+BPF_W+BPF_ABS, \
 154                 offsetof(struct seccomp_data, nr))
 155 #define SC_DENY_UNLESS_MASK(_nr, _arg_nr, _arg_val, _errno) \
 156 /* Special handling for futex(2) that combines a bitmap and operation number */
 157 #if defined(__NR_futex) || defined(__NR_futex_time64)
 158 #define SC_FUTEX_MASK (FUTEX_PRIVATE_FLAG|FUTEX_CLOCK_REALTIME)
 159 #define SC_ALLOW_FUTEX_OP(_nr, _op) \
 160         BPF_JUMP(BPF_JMP+BPF_JEQ+BPF_K, (_nr), 0, 8), \
 161         /* load syscall argument, low word */ \
 162         BPF_STMT(BPF_LD+BPF_W+BPF_ABS, \
 163             offsetof(struct seccomp_data, args[1]) + ARG_LO_OFFSET), \
 164         /* mask off allowed bitmap values, low word */ \
 165         BPF_STMT(BPF_ALU+BPF_AND+BPF_K, ~(SC_FUTEX_MASK & 0xFFFFFFFF)), \
 166         /* test operation number, low word */ \
 167         BPF_JUMP(BPF_JMP+BPF_JEQ+BPF_K, ((_op) & 0xFFFFFFFF), 0, 4), \
 168         /* load syscall argument, high word */ \
 169         BPF_STMT(BPF_LD+BPF_W+BPF_ABS, \
 170             offsetof(struct seccomp_data, args[1]) + ARG_HI_OFFSET), \
 171         /* mask off allowed bitmap values, high word */ \
 172         BPF_STMT(BPF_ALU+BPF_AND+BPF_K, \
 173             ~(((uint32_t)((uint64_t)SC_FUTEX_MASK >> 32)) & 0xFFFFFFFF)), \
 174         /* test operation number, high word */ \
 175         BPF_JUMP(BPF_JMP+BPF_JEQ+BPF_K, \
 176             (((uint32_t)((uint64_t)(_op) >> 32)) & 0xFFFFFFFF), 0, 1), \
 177         BPF_STMT(BPF_RET+BPF_K, SECCOMP_RET_ALLOW), \
 178         /* reload syscall number; all rules expect it in accumulator */ \
 179         BPF_STMT(BPF_LD+BPF_W+BPF_ABS, offsetof(struct seccomp_data, nr))
 180
 181 /* Use this for both __NR_futex and __NR_futex_time64 */
 182 # define SC_FUTEX(_nr) \
 183         SC_ALLOW_FUTEX_OP(__NR_futex, FUTEX_WAIT), \
 184         SC_ALLOW_FUTEX_OP(__NR_futex, FUTEX_WAIT_BITSET), \
 185         SC_ALLOW_FUTEX_OP(__NR_futex, FUTEX_WAKE), \
 186         SC_ALLOW_FUTEX_OP(__NR_futex, FUTEX_WAKE_BITSET), \
 187         SC_ALLOW_FUTEX_OP(__NR_futex, FUTEX_REQUEUE), \
 188         SC_ALLOW_FUTEX_OP(__NR_futex, FUTEX_CMP_REQUEUE)
 189 #endif /* __NR_futex || __NR_futex_time64 */
 190
 191 #if defined(__NR_mmap) || defined(__NR_mmap2)
 192 # ifdef MAP_FIXED_NOREPLACE
 193 #  define SC_MMAP_FLAGS MAP_PRIVATE|MAP_ANONYMOUS|MAP_FIXED|MAP_FIXED_NOREPLACE
 194 # else
 195 #  define SC_MMAP_FLAGS MAP_PRIVATE|MAP_ANONYMOUS|MAP_FIXED
 196 # endif /* MAP_FIXED_NOREPLACE */
 197 /* Use this for both __NR_mmap and __NR_mmap2 variants */
 198 # define SC_MMAP(_nr) \
 199         SC_DENY_UNLESS_ARG_MASK(_nr, 3, SC_MMAP_FLAGS, EINVAL), \
 200         SC_ALLOW_ARG_MASK(_nr, 2, PROT_READ|PROT_WRITE|PROT_NONE)
 201 #endif /* __NR_mmap || __NR_mmap2 */
 202
 203 /* Syscall filtering set for preauth. */
 204 static const struct sock_filter preauth_insns[] = {
 205         /* Ensure the syscall arch convention is as expected. */
 206         BPF_STMT(BPF_LD+BPF_W+BPF_ABS,
 207                 offsetof(struct seccomp_data, arch)),
 208         BPF_JUMP(BPF_JMP+BPF_JEQ+BPF_K, SECCOMP_AUDIT_ARCH, 1, 0),
 209         BPF_STMT(BPF_RET+BPF_K, SECCOMP_FILTER_FAIL),
 210         /* Load the syscall number for checking. */
 211         BPF_STMT(BPF_LD+BPF_W+BPF_ABS,
 212                 offsetof(struct seccomp_data, nr)),
 213
 214         /* Syscalls to non-fatally deny */
 215 #ifdef __NR_lstat
 216         SC_DENY(__NR_lstat, EACCES),
 217 #endif
 218 #ifdef __NR_lstat64
 219         SC_DENY(__NR_lstat64, EACCES),
 220 #endif
 221 #ifdef __NR_fstat
 222         SC_DENY(__NR_fstat, EACCES),
 223 #endif
 224 #ifdef __NR_fstat64
 225         SC_DENY(__NR_fstat64, EACCES),
 226 #endif
 227 #ifdef __NR_fstatat64
 228         SC_DENY(__NR_fstatat64, EACCES),
 229 #endif
 230 #ifdef __NR_open
 231         SC_DENY(__NR_open, EACCES),
 232 #endif
 233 #ifdef __NR_openat
 234         SC_DENY(__NR_openat, EACCES),
 235 #endif
 236 #ifdef __NR_newfstatat
 237         SC_DENY(__NR_newfstatat, EACCES),
 238 #endif
 239 #ifdef __NR_stat
 240         SC_DENY(__NR_stat, EACCES),
 241 #endif
 242 #ifdef __NR_stat64
 243         SC_DENY(__NR_stat64, EACCES),
 244 #endif
 245 #ifdef __NR_shmget
 246         SC_DENY(__NR_shmget, EACCES),
 247 #endif
 248 #ifdef __NR_shmat
 249         SC_DENY(__NR_shmat, EACCES),
 250 #endif
 251 #ifdef __NR_shmdt
 252         SC_DENY(__NR_shmdt, EACCES),
 253 #endif
 254 #ifdef __NR_ipc
 255         SC_DENY(__NR_ipc, EACCES),
 256 #endif
 257 #ifdef __NR_statx
 258         SC_DENY(__NR_statx, EACCES),
 259 #endif
 260
 261         /* Syscalls to permit */
 262 #ifdef __NR_brk
 263         SC_ALLOW(__NR_brk),
 264 #endif
 265 #ifdef __NR_clock_gettime
 266         SC_ALLOW(__NR_clock_gettime),
 267 #endif
 268 #ifdef __NR_clock_gettime64
 269         SC_ALLOW(__NR_clock_gettime64),
 270 #endif
 271 #ifdef __NR_close
 272         SC_ALLOW(__NR_close),
 273 #endif
 274 #ifdef __NR_exit
 275         SC_ALLOW(__NR_exit),
 276 #endif
 277 #ifdef __NR_exit_group
 278         SC_ALLOW(__NR_exit_group),
 279 #endif
 280 #ifdef __NR_futex
 281         SC_FUTEX(__NR_futex),
 282 #endif
 283 #ifdef __NR_futex_time64
 284         SC_FUTEX(__NR_futex_time64),
 285 #endif
 286 #ifdef __NR_geteuid
 287         SC_ALLOW(__NR_geteuid),
 288 #endif
 289 #ifdef __NR_geteuid32
 290         SC_ALLOW(__NR_geteuid32),
 291 #endif
 292 #ifdef __NR_getpgid
 293         SC_ALLOW(__NR_getpgid),
 294 #endif
 295 #ifdef __NR_getpid
 296         SC_ALLOW(__NR_getpid),
 297 #endif
 298 #ifdef __NR_getrandom
 299         SC_ALLOW(__NR_getrandom),
 300 #endif
 301 #ifdef __NR_gettid
 302         SC_ALLOW(__NR_gettid),
 303 #endif
 304 #ifdef __NR_gettimeofday
 305         SC_ALLOW(__NR_gettimeofday),
 306 #endif
 307 #ifdef __NR_getuid
 308         SC_ALLOW(__NR_getuid),
 309 #endif
 310 #ifdef __NR_getuid32
 311         SC_ALLOW(__NR_getuid32),
 312 #endif
 313 #ifdef __NR_madvise
 314         SC_ALLOW_ARG(__NR_madvise, 2, MADV_NORMAL),
 315 # ifdef MADV_FREE
 316         SC_ALLOW_ARG(__NR_madvise, 2, MADV_FREE),
 317 # endif
 318 # ifdef MADV_DONTNEED
 319         SC_ALLOW_ARG(__NR_madvise, 2, MADV_DONTNEED),
 320 # endif
 321 # ifdef MADV_DONTFORK
 322         SC_ALLOW_ARG(__NR_madvise, 2, MADV_DONTFORK),
 323 # endif
 324 # ifdef MADV_DONTDUMP
 325         SC_ALLOW_ARG(__NR_madvise, 2, MADV_DONTDUMP),
 326 # endif
 327 # ifdef MADV_WIPEONFORK
 328         SC_ALLOW_ARG(__NR_madvise, 2, MADV_WIPEONFORK),
 329 # endif
 330         SC_DENY(__NR_madvise, EINVAL),
 331 #endif
 332 #ifdef __NR_mmap
 333         SC_MMAP(__NR_mmap),
 334 #endif
 335 #ifdef __NR_mmap2
 336         SC_MMAP(__NR_mmap2),
 337 #endif
 338 #ifdef __NR_mprotect
 339         SC_ALLOW_ARG_MASK(__NR_mprotect, 2, PROT_READ|PROT_WRITE|PROT_NONE),
 340 #endif
 341 #ifdef __NR_mremap
 342         SC_ALLOW(__NR_mremap),
 343 #endif
 344 #ifdef __NR_munmap
 345         SC_ALLOW(__NR_munmap),
 346 #endif
 347 #ifdef __NR_nanosleep
 348         SC_ALLOW(__NR_nanosleep),
 349 #endif
 350 #ifdef __NR_clock_nanosleep
 351         SC_ALLOW(__NR_clock_nanosleep),
 352 #endif
 353 #ifdef __NR_clock_nanosleep_time64
 354         SC_ALLOW(__NR_clock_nanosleep_time64),
 355 #endif
 356 #ifdef __NR_clock_gettime64
 357         SC_ALLOW(__NR_clock_gettime64),
 358 #endif
 359 #ifdef __NR__newselect
 360         SC_ALLOW(__NR__newselect),
 361 #endif
 362 #ifdef __NR_ppoll
 363         SC_ALLOW(__NR_ppoll),
 364 #endif
 365 #ifdef __NR_ppoll_time64
 366         SC_ALLOW(__NR_ppoll_time64),
 367 #endif
 368 #ifdef __NR_poll
 369         SC_ALLOW(__NR_poll),
 370 #endif
 371 #ifdef __NR_pselect6
 372         SC_ALLOW(__NR_pselect6),
 373 #endif
 374 #ifdef __NR_pselect6_time64
 375         SC_ALLOW(__NR_pselect6_time64),
 376 #endif
 377 #ifdef __NR_read
 378         SC_ALLOW(__NR_read),
 379 #endif
 380 #ifdef __NR_rt_sigprocmask
 381         SC_ALLOW(__NR_rt_sigprocmask),
 382 #endif
 383 #ifdef __NR_select
 384         SC_ALLOW(__NR_select),
 385 #endif
 386 #ifdef __NR_shutdown
 387         SC_ALLOW(__NR_shutdown),
 388 #endif
 389 #ifdef __NR_sigprocmask
 390         SC_ALLOW(__NR_sigprocmask),
 391 #endif
 392 #ifdef __NR_time
 393         SC_ALLOW(__NR_time),
 394 #endif
 395 #ifdef __NR_write
 396         SC_ALLOW(__NR_write),
 397 #endif
 398 #ifdef __NR_writev
 399         SC_ALLOW(__NR_writev),
 400 #endif
 401 #ifdef __NR_socketcall
 402         SC_ALLOW_ARG(__NR_socketcall, 0, SYS_SHUTDOWN),
 403         SC_DENY(__NR_socketcall, EACCES),
 404 #endif
 405 #if defined(__NR_ioctl) && defined(__s390__)
 406         /* Allow ioctls for ICA crypto card on s390 */
 407         SC_ALLOW_ARG(__NR_ioctl, 1, Z90STAT_STATUS_MASK),
 408         SC_ALLOW_ARG(__NR_ioctl, 1, ICARSAMODEXPO),
 409         SC_ALLOW_ARG(__NR_ioctl, 1, ICARSACRT),
 410         SC_ALLOW_ARG(__NR_ioctl, 1, ZSECSENDCPRB),
 411         /* Allow ioctls for EP11 crypto card on s390 */
 412         SC_ALLOW_ARG(__NR_ioctl, 1, ZSENDEP11CPRB),
 413 #endif
 414 #if defined(__x86_64__) && defined(__ILP32__) && defined(__X32_SYSCALL_BIT)
 415         /*
 416          * On Linux x32, the clock_gettime VDSO falls back to the
 417          * x86-64 syscall under some circumstances, e.g.
 418          * https://bugs.debian.org/849923
 419          */
 420         SC_ALLOW(__NR_clock_gettime & ~__X32_SYSCALL_BIT),
 421 #endif
 422
 423         /* Default deny */
 424         BPF_STMT(BPF_RET+BPF_K, SECCOMP_FILTER_FAIL),
 425 };
 426
 427 static const struct sock_fprog preauth_program = {
 428         .len = (unsigned short)(sizeof(preauth_insns)/sizeof(preauth_insns[0])),
 429         .filter = (struct sock_filter *)preauth_insns,
 430 };
 431
 432 struct ssh_sandbox {
 433         pid_t child_pid;
 434 };
 435
 436 struct ssh_sandbox *
 437 ssh_sandbox_init(struct monitor *monitor)
 438 {
 439         struct ssh_sandbox *box;
 440
 441         /*
 442          * Strictly, we don't need to maintain any state here but we need
 443          * to return non-NULL to satisfy the API.
 444          */
 445         debug3("%s: preparing seccomp filter sandbox", __func__);
 446         box = xcalloc(1, sizeof(*box));
 447         box->child_pid = 0;
 448
 449         return box;
 450 }
 451
 452 #ifdef SANDBOX_SECCOMP_FILTER_DEBUG
 453 extern struct monitor *pmonitor;
 454 void mm_log_handler(LogLevel level, int forced, const char *msg, void *ctx);
 455
 456 static void
 457 ssh_sandbox_violation(int signum, siginfo_t *info, void *void_context)
 458 {
 459         char msg[256];
 460
 461         snprintf(msg, sizeof(msg),
 462             "%s: unexpected system call (arch:0x%x,syscall:%d @ %p)",
 463             __func__, info->si_arch, info->si_syscall, info->si_call_addr);
 464         mm_log_handler(SYSLOG_LEVEL_FATAL, 0, msg, pmonitor);
 465         _exit(1);
 466 }
 467
 468 static void
 469 ssh_sandbox_child_debugging(void)
 470 {
 471         struct sigaction act;
 472         sigset_t mask;
 473
 474         debug3("%s: installing SIGSYS handler", __func__);
 475         memset(&act, 0, sizeof(act));
 476         sigemptyset(&mask);
 477         sigaddset(&mask, SIGSYS);
 478
 479         act.sa_sigaction = &ssh_sandbox_violation;
 480         act.sa_flags = SA_SIGINFO;
 481         if (sigaction(SIGSYS, &act, NULL) == -1)
 482                 fatal("%s: sigaction(SIGSYS): %s", __func__, strerror(errno));
 483         if (sigprocmask(SIG_UNBLOCK, &mask, NULL) == -1)
 484                 fatal("%s: sigprocmask(SIGSYS): %s",
 485                     __func__, strerror(errno));
 486 }
 487 #endif /* SANDBOX_SECCOMP_FILTER_DEBUG */
 488
 489 void
 490 ssh_sandbox_child(struct ssh_sandbox *box)
 491 {
 492         struct rlimit rl_zero, rl_one = {.rlim_cur = 1, .rlim_max = 1};
 493         int nnp_failed = 0;
 494
 495         /* Set rlimits for completeness if possible. */
 496         rl_zero.rlim_cur = rl_zero.rlim_max = 0;
 497         if (setrlimit(RLIMIT_FSIZE, &rl_zero) == -1)
 498                 fatal("%s: setrlimit(RLIMIT_FSIZE, { 0, 0 }): %s",
 499                         __func__, strerror(errno));
 500         /*
 501          * Cannot use zero for nfds, because poll(2) will fail with
 502          * errno=EINVAL if npfds>RLIMIT_NOFILE.
 503          */
 504         if (setrlimit(RLIMIT_NOFILE, &rl_one) == -1)
 505                 fatal("%s: setrlimit(RLIMIT_NOFILE, { 0, 0 }): %s",
 506                         __func__, strerror(errno));
 507         if (setrlimit(RLIMIT_NPROC, &rl_zero) == -1)
 508                 fatal("%s: setrlimit(RLIMIT_NPROC, { 0, 0 }): %s",
 509                         __func__, strerror(errno));
 510
 511 #ifdef SANDBOX_SECCOMP_FILTER_DEBUG
 512         ssh_sandbox_child_debugging();
 513 #endif /* SANDBOX_SECCOMP_FILTER_DEBUG */
 514
 515         debug3("%s: setting PR_SET_NO_NEW_PRIVS", __func__);
 516         if (prctl(PR_SET_NO_NEW_PRIVS, 1, 0, 0, 0) == -1) {
 517                 debug("%s: prctl(PR_SET_NO_NEW_PRIVS): %s",
 518                     __func__, strerror(errno));
 519                 nnp_failed = 1;
 520         }
 521         debug3("%s: attaching seccomp filter program", __func__);
 522         if (prctl(PR_SET_SECCOMP, SECCOMP_MODE_FILTER, &preauth_program) == -1)
 523                 debug("%s: prctl(PR_SET_SECCOMP): %s",
 524                     __func__, strerror(errno));
 525         else if (nnp_failed)
 526                 fatal("%s: SECCOMP_MODE_FILTER activated but "
 527                     "PR_SET_NO_NEW_PRIVS failed", __func__);
 528 }
 529
 530 void
 531 ssh_sandbox_parent_finish(struct ssh_sandbox *box)
 532 {
 533         free(box);
 534         debug3("%s: finished", __func__);
 535 }
 536
 537 void
 538 ssh_sandbox_parent_preauth(struct ssh_sandbox *box, pid_t child_pid)
 539 {
 540         box->child_pid = child_pid;
 541 }
 542
 543 #endif /* SANDBOX_SECCOMP_FILTER */