From e0956e38349d4a32f3c4a726af45a3695ff2d3c2 Mon Sep 17 00:00:00 2001 From: Damien Miller Date: Wed, 4 Apr 2012 11:27:54 +1000 Subject: - (djm) [Makefile.in configure.ac sandbox-seccomp-filter.c] Add sandbox mode for Linux's new seccomp filter; patch from Will Drewry; feedback and ok dtucker@ --- sandbox-seccomp-filter.c | 222 +++++++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 222 insertions(+) create mode 100644 sandbox-seccomp-filter.c (limited to 'sandbox-seccomp-filter.c') diff --git a/sandbox-seccomp-filter.c b/sandbox-seccomp-filter.c new file mode 100644 index 000000000..686812957 --- /dev/null +++ b/sandbox-seccomp-filter.c @@ -0,0 +1,222 @@ +/* + * Copyright (c) 2012 Will Drewry + * + * 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= + */ +/* #define SANDBOX_SECCOMP_FILTER_DEBUG 1 */ + +#ifdef SANDBOX_SECCOMP_FILTER_DEBUG +/* Use the kernel headers in case of an older toolchain. */ +# include +# 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 +#include +#include + +#include +#include +#include + +#include + +#include +#include +#include +#include /* for offsetof */ +#include +#include +#include +#include + +#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 */ + +/* 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) + +/* 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)), + SC_DENY(open, EACCES), + SC_ALLOW(getpid), + SC_ALLOW(gettimeofday), + SC_ALLOW(time), + SC_ALLOW(read), + SC_ALLOW(write), + SC_ALLOW(close), + SC_ALLOW(brk), + SC_ALLOW(poll), +#ifdef __NR__newselect + SC_ALLOW(_newselect), +#else + SC_ALLOW(select), +#endif + SC_ALLOW(madvise), + SC_ALLOW(mmap), + SC_ALLOW(munmap), + SC_ALLOW(exit_group), +#ifdef __NR_rt_sigprocmask + SC_ALLOW(rt_sigprocmask), +#else + SC_ALLOW(sigprocmask), +#endif + 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(void) +{ + 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; + + /* 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) + fatal("%s: prctl(PR_SET_NO_NEW_PRIVS): %s", + __func__, strerror(errno)); + debug3("%s: attaching seccomp filter program", __func__); + if (prctl(PR_SET_SECCOMP, SECCOMP_MODE_FILTER, &preauth_program) == -1) + fatal("%s: prctl(PR_SET_SECCOMP): %s", + __func__, strerror(errno)); +} + +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 */ -- cgit v1.2.3