| /* |
| * Copyright (c) 2012 Will Drewry <wad@dataspill.org> |
| * |
| * Permission to use, copy, modify, and distribute this software for any |
| * purpose with or without fee is hereby granted, provided that the above |
| * copyright notice and this permission notice appear in all copies. |
| * |
| * THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES |
| * WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF |
| * MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR |
| * ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES |
| * WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN |
| * ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF |
| * OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE. |
| */ |
| |
| /* |
| * Uncomment the SANDBOX_SECCOMP_FILTER_DEBUG macro below to help diagnose |
| * filter breakage during development. *Do not* use this in production, |
| * as it relies on making library calls that are unsafe in signal context. |
| * |
| * Instead, live systems the auditctl(8) may be used to monitor failures. |
| * E.g. |
| * auditctl -a task,always -F uid=<privsep uid> |
| */ |
| /* #define SANDBOX_SECCOMP_FILTER_DEBUG 1 */ |
| |
| /* XXX it should be possible to do logging via the log socket safely */ |
| |
| #ifdef SANDBOX_SECCOMP_FILTER_DEBUG |
| /* Use the kernel headers in case of an older toolchain. */ |
| # include <asm/siginfo.h> |
| # define __have_siginfo_t 1 |
| # define __have_sigval_t 1 |
| # define __have_sigevent_t 1 |
| #endif /* SANDBOX_SECCOMP_FILTER_DEBUG */ |
| |
| #include "includes.h" |
| |
| #ifdef SANDBOX_SECCOMP_FILTER |
| |
| #include <sys/types.h> |
| #include <sys/resource.h> |
| #include <sys/prctl.h> |
| |
| #include <linux/net.h> |
| #include <linux/audit.h> |
| #include <linux/filter.h> |
| #include <linux/seccomp.h> |
| #include <elf.h> |
| |
| #include <asm/unistd.h> |
| |
| #include <errno.h> |
| #include <signal.h> |
| #include <stdarg.h> |
| #include <stddef.h> /* for offsetof */ |
| #include <stdio.h> |
| #include <stdlib.h> |
| #include <string.h> |
| #include <unistd.h> |
| |
| #include "log.h" |
| #include "ssh-sandbox.h" |
| #include "xmalloc.h" |
| |
| /* Linux seccomp_filter sandbox */ |
| #define SECCOMP_FILTER_FAIL SECCOMP_RET_KILL |
| |
| /* Use a signal handler to emit violations when debugging */ |
| #ifdef SANDBOX_SECCOMP_FILTER_DEBUG |
| # undef SECCOMP_FILTER_FAIL |
| # define SECCOMP_FILTER_FAIL SECCOMP_RET_TRAP |
| #endif /* SANDBOX_SECCOMP_FILTER_DEBUG */ |
| |
| #if __BYTE_ORDER == __LITTLE_ENDIAN |
| # define ARG_LO_OFFSET 0 |
| # define ARG_HI_OFFSET sizeof(uint32_t) |
| #elif __BYTE_ORDER == __BIG_ENDIAN |
| # define ARG_LO_OFFSET sizeof(uint32_t) |
| # define ARG_HI_OFFSET 0 |
| #else |
| #error "Unknown endianness" |
| #endif |
| |
| /* Simple helpers to avoid manual errors (but larger BPF programs). */ |
| #define SC_DENY(_nr, _errno) \ |
| BPF_JUMP(BPF_JMP+BPF_JEQ+BPF_K, __NR_ ## _nr, 0, 1), \ |
| BPF_STMT(BPF_RET+BPF_K, SECCOMP_RET_ERRNO|(_errno)) |
| #define SC_ALLOW(_nr) \ |
| BPF_JUMP(BPF_JMP+BPF_JEQ+BPF_K, __NR_ ## _nr, 0, 1), \ |
| BPF_STMT(BPF_RET+BPF_K, SECCOMP_RET_ALLOW) |
| #define SC_ALLOW_ARG(_nr, _arg_nr, _arg_val) \ |
| BPF_JUMP(BPF_JMP+BPF_JEQ+BPF_K, __NR_ ## _nr, 0, 6), \ |
| /* load and test first syscall argument, low word */ \ |
| BPF_STMT(BPF_LD+BPF_W+BPF_ABS, \ |
| offsetof(struct seccomp_data, args[(_arg_nr)]) + ARG_LO_OFFSET), \ |
| BPF_JUMP(BPF_JMP+BPF_JEQ+BPF_K, \ |
| ((_arg_val) & 0xFFFFFFFF), 0, 3), \ |
| /* load and test first syscall argument, high word */ \ |
| BPF_STMT(BPF_LD+BPF_W+BPF_ABS, \ |
| offsetof(struct seccomp_data, args[(_arg_nr)]) + ARG_HI_OFFSET), \ |
| BPF_JUMP(BPF_JMP+BPF_JEQ+BPF_K, \ |
| (((uint32_t)((uint64_t)(_arg_val) >> 32)) & 0xFFFFFFFF), 0, 1), \ |
| BPF_STMT(BPF_RET+BPF_K, SECCOMP_RET_ALLOW), \ |
| /* reload syscall number; all rules expect it in accumulator */ \ |
| BPF_STMT(BPF_LD+BPF_W+BPF_ABS, \ |
| offsetof(struct seccomp_data, nr)) |
| |
| /* Syscall filtering set for preauth. */ |
| static const struct sock_filter preauth_insns[] = { |
| /* Ensure the syscall arch convention is as expected. */ |
| BPF_STMT(BPF_LD+BPF_W+BPF_ABS, |
| offsetof(struct seccomp_data, arch)), |
| BPF_JUMP(BPF_JMP+BPF_JEQ+BPF_K, SECCOMP_AUDIT_ARCH, 1, 0), |
| BPF_STMT(BPF_RET+BPF_K, SECCOMP_FILTER_FAIL), |
| /* Load the syscall number for checking. */ |
| BPF_STMT(BPF_LD+BPF_W+BPF_ABS, |
| offsetof(struct seccomp_data, nr)), |
| |
| /* Syscalls to non-fatally deny */ |
| #ifdef __NR_lstat |
| SC_DENY(lstat, EACCES), |
| #endif |
| #ifdef __NR_lstat64 |
| SC_DENY(lstat64, EACCES), |
| #endif |
| #ifdef __NR_fstat |
| SC_DENY(fstat, EACCES), |
| #endif |
| #ifdef __NR_fstat64 |
| SC_DENY(fstat64, EACCES), |
| #endif |
| #ifdef __NR_open |
| SC_DENY(open, EACCES), |
| #endif |
| #ifdef __NR_openat |
| SC_DENY(openat, EACCES), |
| #endif |
| #ifdef __NR_newfstatat |
| SC_DENY(newfstatat, EACCES), |
| #endif |
| #ifdef __NR_stat |
| SC_DENY(stat, EACCES), |
| #endif |
| #ifdef __NR_stat64 |
| SC_DENY(stat64, EACCES), |
| #endif |
| |
| /* Syscalls to permit */ |
| #ifdef __NR_brk |
| SC_ALLOW(brk), |
| #endif |
| #ifdef __NR_clock_gettime |
| SC_ALLOW(clock_gettime), |
| #endif |
| #ifdef __NR_close |
| SC_ALLOW(close), |
| #endif |
| #ifdef __NR_exit |
| SC_ALLOW(exit), |
| #endif |
| #ifdef __NR_exit_group |
| SC_ALLOW(exit_group), |
| #endif |
| #ifdef __NR_getpgid |
| SC_ALLOW(getpgid), |
| #endif |
| #ifdef __NR_getpid |
| SC_ALLOW(getpid), |
| #endif |
| #ifdef __NR_getrandom |
| SC_ALLOW(getrandom), |
| #endif |
| #ifdef __NR_gettimeofday |
| SC_ALLOW(gettimeofday), |
| #endif |
| #ifdef __NR_madvise |
| SC_ALLOW(madvise), |
| #endif |
| #ifdef __NR_mmap |
| SC_ALLOW(mmap), |
| #endif |
| #ifdef __NR_mmap2 |
| SC_ALLOW(mmap2), |
| #endif |
| #ifdef __NR_mremap |
| SC_ALLOW(mremap), |
| #endif |
| #ifdef __NR_munmap |
| SC_ALLOW(munmap), |
| #endif |
| #ifdef __NR__newselect |
| SC_ALLOW(_newselect), |
| #endif |
| #ifdef __NR_poll |
| SC_ALLOW(poll), |
| #endif |
| #ifdef __NR_pselect6 |
| SC_ALLOW(pselect6), |
| #endif |
| #ifdef __NR_read |
| SC_ALLOW(read), |
| #endif |
| #ifdef __NR_rt_sigprocmask |
| SC_ALLOW(rt_sigprocmask), |
| #endif |
| #ifdef __NR_select |
| SC_ALLOW(select), |
| #endif |
| #ifdef __NR_shutdown |
| SC_ALLOW(shutdown), |
| #endif |
| #ifdef __NR_sigprocmask |
| SC_ALLOW(sigprocmask), |
| #endif |
| #ifdef __NR_time |
| SC_ALLOW(time), |
| #endif |
| #ifdef __NR_write |
| SC_ALLOW(write), |
| #endif |
| #ifdef __NR_socketcall |
| SC_ALLOW_ARG(socketcall, 0, SYS_SHUTDOWN), |
| #endif |
| |
| /* Default deny */ |
| BPF_STMT(BPF_RET+BPF_K, SECCOMP_FILTER_FAIL), |
| }; |
| |
| static const struct sock_fprog preauth_program = { |
| .len = (unsigned short)(sizeof(preauth_insns)/sizeof(preauth_insns[0])), |
| .filter = (struct sock_filter *)preauth_insns, |
| }; |
| |
| struct ssh_sandbox { |
| pid_t child_pid; |
| }; |
| |
| struct ssh_sandbox * |
| ssh_sandbox_init(struct monitor *monitor) |
| { |
| struct ssh_sandbox *box; |
| |
| /* |
| * Strictly, we don't need to maintain any state here but we need |
| * to return non-NULL to satisfy the API. |
| */ |
| debug3("%s: preparing seccomp filter sandbox", __func__); |
| box = xcalloc(1, sizeof(*box)); |
| box->child_pid = 0; |
| |
| return box; |
| } |
| |
| #ifdef SANDBOX_SECCOMP_FILTER_DEBUG |
| extern struct monitor *pmonitor; |
| void mm_log_handler(LogLevel level, const char *msg, void *ctx); |
| |
| static void |
| ssh_sandbox_violation(int signum, siginfo_t *info, void *void_context) |
| { |
| char msg[256]; |
| |
| snprintf(msg, sizeof(msg), |
| "%s: unexpected system call (arch:0x%x,syscall:%d @ %p)", |
| __func__, info->si_arch, info->si_syscall, info->si_call_addr); |
| mm_log_handler(SYSLOG_LEVEL_FATAL, msg, pmonitor); |
| _exit(1); |
| } |
| |
| static void |
| ssh_sandbox_child_debugging(void) |
| { |
| struct sigaction act; |
| sigset_t mask; |
| |
| debug3("%s: installing SIGSYS handler", __func__); |
| memset(&act, 0, sizeof(act)); |
| sigemptyset(&mask); |
| sigaddset(&mask, SIGSYS); |
| |
| act.sa_sigaction = &ssh_sandbox_violation; |
| act.sa_flags = SA_SIGINFO; |
| if (sigaction(SIGSYS, &act, NULL) == -1) |
| fatal("%s: sigaction(SIGSYS): %s", __func__, strerror(errno)); |
| if (sigprocmask(SIG_UNBLOCK, &mask, NULL) == -1) |
| fatal("%s: sigprocmask(SIGSYS): %s", |
| __func__, strerror(errno)); |
| } |
| #endif /* SANDBOX_SECCOMP_FILTER_DEBUG */ |
| |
| void |
| ssh_sandbox_child(struct ssh_sandbox *box) |
| { |
| struct rlimit rl_zero; |
| int nnp_failed = 0; |
| |
| /* Set rlimits for completeness if possible. */ |
| rl_zero.rlim_cur = rl_zero.rlim_max = 0; |
| if (setrlimit(RLIMIT_FSIZE, &rl_zero) == -1) |
| fatal("%s: setrlimit(RLIMIT_FSIZE, { 0, 0 }): %s", |
| __func__, strerror(errno)); |
| if (setrlimit(RLIMIT_NOFILE, &rl_zero) == -1) |
| fatal("%s: setrlimit(RLIMIT_NOFILE, { 0, 0 }): %s", |
| __func__, strerror(errno)); |
| if (setrlimit(RLIMIT_NPROC, &rl_zero) == -1) |
| fatal("%s: setrlimit(RLIMIT_NPROC, { 0, 0 }): %s", |
| __func__, strerror(errno)); |
| |
| #ifdef SANDBOX_SECCOMP_FILTER_DEBUG |
| ssh_sandbox_child_debugging(); |
| #endif /* SANDBOX_SECCOMP_FILTER_DEBUG */ |
| |
| debug3("%s: setting PR_SET_NO_NEW_PRIVS", __func__); |
| if (prctl(PR_SET_NO_NEW_PRIVS, 1, 0, 0, 0) == -1) { |
| debug("%s: prctl(PR_SET_NO_NEW_PRIVS): %s", |
| __func__, strerror(errno)); |
| nnp_failed = 1; |
| } |
| debug3("%s: attaching seccomp filter program", __func__); |
| if (prctl(PR_SET_SECCOMP, SECCOMP_MODE_FILTER, &preauth_program) == -1) |
| debug("%s: prctl(PR_SET_SECCOMP): %s", |
| __func__, strerror(errno)); |
| else if (nnp_failed) |
| fatal("%s: SECCOMP_MODE_FILTER activated but " |
| "PR_SET_NO_NEW_PRIVS failed", __func__); |
| } |
| |
| void |
| ssh_sandbox_parent_finish(struct ssh_sandbox *box) |
| { |
| free(box); |
| debug3("%s: finished", __func__); |
| } |
| |
| void |
| ssh_sandbox_parent_preauth(struct ssh_sandbox *box, pid_t child_pid) |
| { |
| box->child_pid = child_pid; |
| } |
| |
| #endif /* SANDBOX_SECCOMP_FILTER */ |