58d839214e
branch but never merged to head. They were inadvertantly left out when 6.1p1 was merged to head. It didn't make any difference at the time, because they were unused, but one of them is required for DNS-based host key verification. Approved by: re (blanket)
237 lines
6.5 KiB
C
237 lines
6.5 KiB
C
/*
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* Copyright (c) 2012 Will Drewry <wad@dataspill.org>
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*
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* Permission to use, copy, modify, and distribute this software for any
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* purpose with or without fee is hereby granted, provided that the above
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* copyright notice and this permission notice appear in all copies.
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*
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* THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
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* WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
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* MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
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* ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
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* WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
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* ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
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* OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
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*/
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/*
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* Uncomment the SANDBOX_SECCOMP_FILTER_DEBUG macro below to help diagnose
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* filter breakage during development. *Do not* use this in production,
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* as it relies on making library calls that are unsafe in signal context.
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*
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* Instead, live systems the auditctl(8) may be used to monitor failures.
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* E.g.
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* auditctl -a task,always -F uid=<privsep uid>
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*/
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/* #define SANDBOX_SECCOMP_FILTER_DEBUG 1 */
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#ifdef SANDBOX_SECCOMP_FILTER_DEBUG
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/* Use the kernel headers in case of an older toolchain. */
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# include <asm/siginfo.h>
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# define __have_siginfo_t 1
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# define __have_sigval_t 1
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# define __have_sigevent_t 1
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#endif /* SANDBOX_SECCOMP_FILTER_DEBUG */
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#include "includes.h"
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#ifdef SANDBOX_SECCOMP_FILTER
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#include <sys/types.h>
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#include <sys/resource.h>
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#include <sys/prctl.h>
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#include <linux/audit.h>
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#include <linux/filter.h>
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#include <linux/seccomp.h>
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#include <elf.h>
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#include <asm/unistd.h>
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#include <errno.h>
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#include <signal.h>
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#include <stdarg.h>
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#include <stddef.h> /* for offsetof */
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#include <stdio.h>
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#include <stdlib.h>
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#include <string.h>
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#include <unistd.h>
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#include "log.h"
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#include "ssh-sandbox.h"
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#include "xmalloc.h"
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/* Linux seccomp_filter sandbox */
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#define SECCOMP_FILTER_FAIL SECCOMP_RET_KILL
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/* Use a signal handler to emit violations when debugging */
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#ifdef SANDBOX_SECCOMP_FILTER_DEBUG
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# undef SECCOMP_FILTER_FAIL
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# define SECCOMP_FILTER_FAIL SECCOMP_RET_TRAP
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#endif /* SANDBOX_SECCOMP_FILTER_DEBUG */
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/* Simple helpers to avoid manual errors (but larger BPF programs). */
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#define SC_DENY(_nr, _errno) \
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BPF_JUMP(BPF_JMP+BPF_JEQ+BPF_K, __NR_ ## _nr, 0, 1), \
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BPF_STMT(BPF_RET+BPF_K, SECCOMP_RET_ERRNO|(_errno))
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#define SC_ALLOW(_nr) \
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BPF_JUMP(BPF_JMP+BPF_JEQ+BPF_K, __NR_ ## _nr, 0, 1), \
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BPF_STMT(BPF_RET+BPF_K, SECCOMP_RET_ALLOW)
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/* Syscall filtering set for preauth. */
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static const struct sock_filter preauth_insns[] = {
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/* Ensure the syscall arch convention is as expected. */
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BPF_STMT(BPF_LD+BPF_W+BPF_ABS,
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offsetof(struct seccomp_data, arch)),
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BPF_JUMP(BPF_JMP+BPF_JEQ+BPF_K, SECCOMP_AUDIT_ARCH, 1, 0),
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BPF_STMT(BPF_RET+BPF_K, SECCOMP_FILTER_FAIL),
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/* Load the syscall number for checking. */
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BPF_STMT(BPF_LD+BPF_W+BPF_ABS,
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offsetof(struct seccomp_data, nr)),
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SC_DENY(open, EACCES),
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SC_ALLOW(getpid),
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SC_ALLOW(gettimeofday),
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#ifdef __NR_time /* not defined on EABI ARM */
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SC_ALLOW(time),
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#endif
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SC_ALLOW(read),
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SC_ALLOW(write),
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SC_ALLOW(close),
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SC_ALLOW(brk),
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SC_ALLOW(poll),
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#ifdef __NR__newselect
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SC_ALLOW(_newselect),
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#else
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SC_ALLOW(select),
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#endif
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SC_ALLOW(madvise),
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#ifdef __NR_mmap2 /* EABI ARM only has mmap2() */
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SC_ALLOW(mmap2),
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#endif
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#ifdef __NR_mmap
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SC_ALLOW(mmap),
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#endif
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SC_ALLOW(munmap),
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SC_ALLOW(exit_group),
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#ifdef __NR_rt_sigprocmask
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SC_ALLOW(rt_sigprocmask),
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#else
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SC_ALLOW(sigprocmask),
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#endif
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BPF_STMT(BPF_RET+BPF_K, SECCOMP_FILTER_FAIL),
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};
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static const struct sock_fprog preauth_program = {
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.len = (unsigned short)(sizeof(preauth_insns)/sizeof(preauth_insns[0])),
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.filter = (struct sock_filter *)preauth_insns,
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};
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struct ssh_sandbox {
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pid_t child_pid;
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};
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struct ssh_sandbox *
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ssh_sandbox_init(void)
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{
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struct ssh_sandbox *box;
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/*
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* Strictly, we don't need to maintain any state here but we need
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* to return non-NULL to satisfy the API.
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*/
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debug3("%s: preparing seccomp filter sandbox", __func__);
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box = xcalloc(1, sizeof(*box));
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box->child_pid = 0;
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return box;
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}
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#ifdef SANDBOX_SECCOMP_FILTER_DEBUG
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extern struct monitor *pmonitor;
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void mm_log_handler(LogLevel level, const char *msg, void *ctx);
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static void
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ssh_sandbox_violation(int signum, siginfo_t *info, void *void_context)
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{
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char msg[256];
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snprintf(msg, sizeof(msg),
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"%s: unexpected system call (arch:0x%x,syscall:%d @ %p)",
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__func__, info->si_arch, info->si_syscall, info->si_call_addr);
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mm_log_handler(SYSLOG_LEVEL_FATAL, msg, pmonitor);
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_exit(1);
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}
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static void
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ssh_sandbox_child_debugging(void)
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{
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struct sigaction act;
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sigset_t mask;
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debug3("%s: installing SIGSYS handler", __func__);
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memset(&act, 0, sizeof(act));
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sigemptyset(&mask);
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sigaddset(&mask, SIGSYS);
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act.sa_sigaction = &ssh_sandbox_violation;
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act.sa_flags = SA_SIGINFO;
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if (sigaction(SIGSYS, &act, NULL) == -1)
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fatal("%s: sigaction(SIGSYS): %s", __func__, strerror(errno));
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if (sigprocmask(SIG_UNBLOCK, &mask, NULL) == -1)
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fatal("%s: sigprocmask(SIGSYS): %s",
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__func__, strerror(errno));
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}
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#endif /* SANDBOX_SECCOMP_FILTER_DEBUG */
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void
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ssh_sandbox_child(struct ssh_sandbox *box)
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{
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struct rlimit rl_zero;
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int nnp_failed = 0;
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/* Set rlimits for completeness if possible. */
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rl_zero.rlim_cur = rl_zero.rlim_max = 0;
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if (setrlimit(RLIMIT_FSIZE, &rl_zero) == -1)
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fatal("%s: setrlimit(RLIMIT_FSIZE, { 0, 0 }): %s",
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__func__, strerror(errno));
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if (setrlimit(RLIMIT_NOFILE, &rl_zero) == -1)
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fatal("%s: setrlimit(RLIMIT_NOFILE, { 0, 0 }): %s",
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__func__, strerror(errno));
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if (setrlimit(RLIMIT_NPROC, &rl_zero) == -1)
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fatal("%s: setrlimit(RLIMIT_NPROC, { 0, 0 }): %s",
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__func__, strerror(errno));
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#ifdef SANDBOX_SECCOMP_FILTER_DEBUG
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ssh_sandbox_child_debugging();
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#endif /* SANDBOX_SECCOMP_FILTER_DEBUG */
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debug3("%s: setting PR_SET_NO_NEW_PRIVS", __func__);
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if (prctl(PR_SET_NO_NEW_PRIVS, 1, 0, 0, 0) == -1) {
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debug("%s: prctl(PR_SET_NO_NEW_PRIVS): %s",
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__func__, strerror(errno));
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nnp_failed = 1;
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}
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debug3("%s: attaching seccomp filter program", __func__);
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if (prctl(PR_SET_SECCOMP, SECCOMP_MODE_FILTER, &preauth_program) == -1)
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debug("%s: prctl(PR_SET_SECCOMP): %s",
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__func__, strerror(errno));
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else if (nnp_failed)
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fatal("%s: SECCOMP_MODE_FILTER activated but "
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"PR_SET_NO_NEW_PRIVS failed", __func__);
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}
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void
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ssh_sandbox_parent_finish(struct ssh_sandbox *box)
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{
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free(box);
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debug3("%s: finished", __func__);
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}
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void
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ssh_sandbox_parent_preauth(struct ssh_sandbox *box, pid_t child_pid)
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{
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box->child_pid = child_pid;
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}
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#endif /* SANDBOX_SECCOMP_FILTER */
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