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freebsd-dev/crypto/openssh/sandbox-seccomp-filter.c
Ed Maste f374ba41f5 ssh: update to OpenSSH 9.2p1 
Release notes are available at https://www.openssh.com/txt/release-9.2

OpenSSH 9.2 contains fixes for two security problems and a memory safety
problem.  The memory safety problem is not believed to be exploitable.
These fixes have already been committed to OpenSSH 9.1 in FreeBSD.

Some other notable items from the release notes:

 * ssh(1): add a new EnableEscapeCommandline ssh_config(5) option that
   controls whether the client-side ~C escape sequence that provides a
   command-line is available. Among other things, the ~C command-line
   could be used to add additional port-forwards at runtime.

 * sshd(8): add support for channel inactivity timeouts via a new
   sshd_config(5) ChannelTimeout directive. This allows channels that
   have not seen traffic in a configurable interval to be
   automatically closed. Different timeouts may be applied to session,
   X11, agent and TCP forwarding channels.

 * sshd(8): add a sshd_config UnusedConnectionTimeout option to
   terminate client connections that have no open channels for a
   length of time. This complements the ChannelTimeout option above.
    
 * sshd(8): add a -V (version) option to sshd like the ssh client has.

 * scp(1), sftp(1): add a -X option to both scp(1) and sftp(1) to
   allow control over some SFTP protocol parameters: the copy buffer
   length and the number of in-flight requests, both of which are used
   during upload/download. Previously these could be controlled in
   sftp(1) only. This makes them available in both SFTP protocol
   clients using the same option character sequence.
    
 * ssh-keyscan(1): allow scanning of complete CIDR address ranges,
   e.g.  "ssh-keyscan 192.168.0.0/24". If a CIDR range is passed, then
   it will be expanded to all possible addresses in the range
   including the all-0s and all-1s addresses. bz#976

 * ssh(1): support dynamic remote port forwarding in escape
   command-line's -R processing. bz#3499

MFC after:	1 week
Sponsored by:	The FreeBSD Foundation
2023-02-06 16:54:56 -05:00

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/*
* 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 */
#if 0
/*
* For older toolchains, it may be necessary to use the kernel
* headers directly.
*/
#ifdef SANDBOX_SECCOMP_FILTER_DEBUG
# include <asm/siginfo.h>
# define __have_siginfo_t 1
# define __have_sigval_t 1
# define __have_sigevent_t 1
#endif /* SANDBOX_SECCOMP_FILTER_DEBUG */
#endif
#include "includes.h"
#ifdef SANDBOX_SECCOMP_FILTER
#include <sys/types.h>
#include <sys/resource.h>
#include <sys/prctl.h>
#include <sys/mman.h>
#include <sys/syscall.h>
#include <linux/net.h>
#include <linux/audit.h>
#include <linux/filter.h>
#include <linux/seccomp.h>
#include <elf.h>
#include <asm/unistd.h>
#ifdef __s390__
#include <asm/zcrypt.h>
#endif
#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), 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), 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), 0, 6), \
/* load and test 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 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))
/* Allow if syscall argument contains only values in mask */
#define SC_ALLOW_ARG_MASK(_nr, _arg_nr, _arg_mask) \
BPF_JUMP(BPF_JMP+BPF_JEQ+BPF_K, (_nr), 0, 8), \
/* load, mask and test syscall argument, low word */ \
BPF_STMT(BPF_LD+BPF_W+BPF_ABS, \
offsetof(struct seccomp_data, args[(_arg_nr)]) + ARG_LO_OFFSET), \
BPF_STMT(BPF_ALU+BPF_AND+BPF_K, ~((_arg_mask) & 0xFFFFFFFF)), \
BPF_JUMP(BPF_JMP+BPF_JEQ+BPF_K, 0, 0, 4), \
/* load, mask and test syscall argument, high word */ \
BPF_STMT(BPF_LD+BPF_W+BPF_ABS, \
offsetof(struct seccomp_data, args[(_arg_nr)]) + ARG_HI_OFFSET), \
BPF_STMT(BPF_ALU+BPF_AND+BPF_K, \
~(((uint32_t)((uint64_t)(_arg_mask) >> 32)) & 0xFFFFFFFF)), \
BPF_JUMP(BPF_JMP+BPF_JEQ+BPF_K, 0, 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(__NR_lstat, EACCES),
#endif
#ifdef __NR_lstat64
SC_DENY(__NR_lstat64, EACCES),
#endif
#ifdef __NR_fstat
SC_DENY(__NR_fstat, EACCES),
#endif
#ifdef __NR_fstat64
SC_DENY(__NR_fstat64, EACCES),
#endif
#ifdef __NR_fstatat64
SC_DENY(__NR_fstatat64, EACCES),
#endif
#ifdef __NR_open
SC_DENY(__NR_open, EACCES),
#endif
#ifdef __NR_openat
SC_DENY(__NR_openat, EACCES),
#endif
#ifdef __NR_newfstatat
SC_DENY(__NR_newfstatat, EACCES),
#endif
#ifdef __NR_stat
SC_DENY(__NR_stat, EACCES),
#endif
#ifdef __NR_stat64
SC_DENY(__NR_stat64, EACCES),
#endif
#ifdef __NR_shmget
SC_DENY(__NR_shmget, EACCES),
#endif
#ifdef __NR_shmat
SC_DENY(__NR_shmat, EACCES),
#endif
#ifdef __NR_shmdt
SC_DENY(__NR_shmdt, EACCES),
#endif
#ifdef __NR_ipc
SC_DENY(__NR_ipc, EACCES),
#endif
#ifdef __NR_statx
SC_DENY(__NR_statx, EACCES),
#endif
/* Syscalls to permit */
#ifdef __NR_brk
SC_ALLOW(__NR_brk),
#endif
#ifdef __NR_clock_gettime
SC_ALLOW(__NR_clock_gettime),
#endif
#ifdef __NR_clock_gettime64
SC_ALLOW(__NR_clock_gettime64),
#endif
#ifdef __NR_close
SC_ALLOW(__NR_close),
#endif
#ifdef __NR_exit
SC_ALLOW(__NR_exit),
#endif
#ifdef __NR_exit_group
SC_ALLOW(__NR_exit_group),
#endif
#ifdef __NR_futex
SC_ALLOW(__NR_futex),
#endif
#ifdef __NR_futex_time64
SC_ALLOW(__NR_futex_time64),
#endif
#ifdef __NR_geteuid
SC_ALLOW(__NR_geteuid),
#endif
#ifdef __NR_geteuid32
SC_ALLOW(__NR_geteuid32),
#endif
#ifdef __NR_getpgid
SC_ALLOW(__NR_getpgid),
#endif
#ifdef __NR_getpid
SC_ALLOW(__NR_getpid),
#endif
#ifdef __NR_getrandom
SC_ALLOW(__NR_getrandom),
#endif
#ifdef __NR_gettid
SC_ALLOW(__NR_gettid),
#endif
#ifdef __NR_gettimeofday
SC_ALLOW(__NR_gettimeofday),
#endif
#ifdef __NR_getuid
SC_ALLOW(__NR_getuid),
#endif
#ifdef __NR_getuid32
SC_ALLOW(__NR_getuid32),
#endif
#ifdef __NR_madvise
SC_ALLOW(__NR_madvise),
#endif
#ifdef __NR_mmap
SC_ALLOW_ARG_MASK(__NR_mmap, 2, PROT_READ|PROT_WRITE|PROT_NONE),
#endif
#ifdef __NR_mmap2
SC_ALLOW_ARG_MASK(__NR_mmap2, 2, PROT_READ|PROT_WRITE|PROT_NONE),
#endif
#ifdef __NR_mprotect
SC_ALLOW_ARG_MASK(__NR_mprotect, 2, PROT_READ|PROT_WRITE|PROT_NONE),
#endif
#ifdef __NR_mremap
SC_ALLOW(__NR_mremap),
#endif
#ifdef __NR_munmap
SC_ALLOW(__NR_munmap),
#endif
#ifdef __NR_nanosleep
SC_ALLOW(__NR_nanosleep),
#endif
#ifdef __NR_clock_nanosleep
SC_ALLOW(__NR_clock_nanosleep),
#endif
#ifdef __NR_clock_nanosleep_time64
SC_ALLOW(__NR_clock_nanosleep_time64),
#endif
#ifdef __NR_clock_gettime64
SC_ALLOW(__NR_clock_gettime64),
#endif
#ifdef __NR__newselect
SC_ALLOW(__NR__newselect),
#endif
#ifdef __NR_ppoll
SC_ALLOW(__NR_ppoll),
#endif
#ifdef __NR_ppoll_time64
SC_ALLOW(__NR_ppoll_time64),
#endif
#ifdef __NR_poll
SC_ALLOW(__NR_poll),
#endif
#ifdef __NR_pselect6
SC_ALLOW(__NR_pselect6),
#endif
#ifdef __NR_pselect6_time64
SC_ALLOW(__NR_pselect6_time64),
#endif
#ifdef __NR_read
SC_ALLOW(__NR_read),
#endif
#ifdef __NR_rt_sigprocmask
SC_ALLOW(__NR_rt_sigprocmask),
#endif
#ifdef __NR_select
SC_ALLOW(__NR_select),
#endif
#ifdef __NR_shutdown
SC_ALLOW(__NR_shutdown),
#endif
#ifdef __NR_sigprocmask
SC_ALLOW(__NR_sigprocmask),
#endif
#ifdef __NR_time
SC_ALLOW(__NR_time),
#endif
#ifdef __NR_write
SC_ALLOW(__NR_write),
#endif
#ifdef __NR_writev
SC_ALLOW(__NR_writev),
#endif
#ifdef __NR_socketcall
SC_ALLOW_ARG(__NR_socketcall, 0, SYS_SHUTDOWN),
SC_DENY(__NR_socketcall, EACCES),
#endif
#if defined(__NR_ioctl) && defined(__s390__)
/* Allow ioctls for ICA crypto card on s390 */
SC_ALLOW_ARG(__NR_ioctl, 1, Z90STAT_STATUS_MASK),
SC_ALLOW_ARG(__NR_ioctl, 1, ICARSAMODEXPO),
SC_ALLOW_ARG(__NR_ioctl, 1, ICARSACRT),
SC_ALLOW_ARG(__NR_ioctl, 1, ZSECSENDCPRB),
/* Allow ioctls for EP11 crypto card on s390 */
SC_ALLOW_ARG(__NR_ioctl, 1, ZSENDEP11CPRB),
#endif
#if defined(__x86_64__) && defined(__ILP32__) && defined(__X32_SYSCALL_BIT)
/*
* On Linux x32, the clock_gettime VDSO falls back to the
* x86-64 syscall under some circumstances, e.g.
* https://bugs.debian.org/849923
*/
SC_ALLOW(__NR_clock_gettime & ~__X32_SYSCALL_BIT),
#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, int forced, 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, 0, 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, rl_one = {.rlim_cur = 1, .rlim_max = 1};
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));
/*
* Cannot use zero for nfds, because poll(2) will fail with
* errno=EINVAL if npfds>RLIMIT_NOFILE.
*/
if (setrlimit(RLIMIT_NOFILE, &rl_one) == -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 */
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