- (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@

4 files changed, 295 insertions, 5 deletions

diff --git a/ChangeLog b/ChangeLog
index 2bd907cc5..a89bb4b5a 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,8 @@
+20120404
+ - (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@
+
 20120330
  - (dtucker) [contrib/redhat/openssh.spec] Bug #1992: remove now-gone WARNING
    file from spec file.  From crighter at nuclioss com.
diff --git a/Makefile.in b/Makefile.in
index 3be3aa617..566f58fe6 100644
--- a/Makefile.in
+++ b/Makefile.in
@@ -1,4 +1,4 @@
-# $Id: Makefile.in,v 1.325 2011/08/05 20:15:18 djm Exp $
+# $Id: Makefile.in,v 1.326 2012/04/04 01:27:57 djm Exp $
 
 # uncomment if you run a non bourne compatable shell. Ie. csh
 #SHELL = @SH@
@@ -90,7 +90,8 @@ SSHDOBJS=sshd.o auth-rhosts.o auth-passwd.o auth-rsa.o auth-rh-rsa.o \
         loginrec.o auth-pam.o auth-shadow.o auth-sia.o md5crypt.o \
         sftp-server.o sftp-common.o \
         roaming_common.o roaming_serv.o \
-        sandbox-null.o sandbox-rlimit.o sandbox-systrace.o sandbox-darwin.o
+        sandbox-null.o sandbox-rlimit.o sandbox-systrace.o sandbox-darwin.o \
+        sandbox-seccomp-filter.o
 
 MANPAGES        = moduli.5.out scp.1.out ssh-add.1.out ssh-agent.1.out ssh-keygen.1.out ssh-keyscan.1.out ssh.1.out sshd.8.out sftp-server.8.out sftp.1.out ssh-keysign.8.out ssh-pkcs11-helper.8.out sshd_config.5.out ssh_config.5.out
 MANPAGES_IN     = moduli.5 scp.1 ssh-add.1 ssh-agent.1 ssh-keygen.1 ssh-keyscan.1 ssh.1 sshd.8 sftp-server.8 sftp.1 ssh-keysign.8 ssh-pkcs11-helper.8 sshd_config.5 ssh_config.5
diff --git a/configure.ac b/configure.ac
index acf529b04..23ac1490a 100644
--- a/configure.ac
+++ b/configure.ac
@@ -1,4 +1,4 @@
-# $Id: configure.ac,v 1.487 2012/02/23 23:40:43 dtucker Exp $
+# $Id: configure.ac,v 1.488 2012/04/04 01:27:57 djm Exp $
 #
 # Copyright (c) 1999-2004 Damien Miller
 #
@@ -15,7 +15,7 @@
 # OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
 
 AC_INIT([OpenSSH], [Portable], [openssh-unix-dev@mindrot.org])
-AC_REVISION($Revision: 1.487 $)
+AC_REVISION($Revision: 1.488 $)
 AC_CONFIG_SRCDIR([ssh.c])
 AC_LANG([C])
 
@@ -116,6 +116,35 @@ AC_CHECK_DECL([RLIMIT_NPROC],
         #include <sys/types.h>
         #include <sys/resource.h>
 ])
+AC_CHECK_DECL([PR_SET_NO_NEW_PRIVS], [have_linux_no_new_privs=1], , [
+        #include <sys/types.h>
+        #include <linux/prctl.h>
+])
+if test "x$have_linux_no_new_privs" = "x1" ; then
+AC_CHECK_DECL([SECCOMP_MODE_FILTER], [have_seccomp_filter=1], , [
+        #include <sys/types.h>
+        #include <linux/seccomp.h>
+])
+fi
+if test "x$have_seccomp_filter" = "x1" ; then
+AC_MSG_CHECKING([kernel for seccomp_filter support])
+AC_RUN_IFELSE([AC_LANG_PROGRAM([[
+                #include <errno.h>
+                #include <linux/seccomp.h>
+                #include <stdlib.h>
+                #include <sys/prctl.h>
+        ]],
+        [[ errno = 0;
+           prctl(PR_SET_SECCOMP, SECCOMP_MODE_FILTER, NULL, 0, 0);
+           exit(errno == EFAULT ? 0 : 1); ]])],
+        [ AC_MSG_RESULT([yes]) ], [
+                AC_MSG_RESULT([no])
+                # Disable seccomp filter as a target
+                have_seccomp_filter=0
+        ],
+        [ AC_MSG_RESULT([cross-compiling, assuming yes]) ]
+)
+fi
 
 use_stack_protector=1
 AC_ARG_WITH([stackprotect],
@@ -657,6 +686,22 @@ main() { if (NSVersionOfRunTimeLibrary("System") >= (60 << 16))
                 AC_DEFINE([SSH_TUN_PREPEND_AF], [1],
                     [Prepend the address family to IP tunnel traffic])
         fi
+        AC_CHECK_HEADERS([linux/seccomp.h linux/filter.h linux/audit.h])
+        AC_CHECK_FUNCS([prctl])
+        have_seccomp_audit_arch=1
+        case "$host" in
+        x86_64-*)
+                AC_DEFINE([SECCOMP_AUDIT_ARCH], [AUDIT_ARCH_X86_64],
+                    [Specify the system call convention in use])
+                ;;
+        i*86-*)
+                AC_DEFINE([SECCOMP_AUDIT_ARCH], [AUDIT_ARCH_I386],
+                    [Specify the system call convention in use])
+                ;;
+        *)
+                have_seccomp_audit_arch=0
+                ;;
+        esac
         ;;
 mips-sony-bsd|mips-sony-newsos4)
         AC_DEFINE([NEED_SETPGRP], [1], [Need setpgrp to acquire controlling tty])
@@ -2518,7 +2563,7 @@ AC_SUBST([SSH_PRIVSEP_USER])
 # Decide which sandbox style to use
 sandbox_arg=""
 AC_ARG_WITH([sandbox],
-        [  --with-sandbox=style    Specify privilege separation sandbox (no, darwin, rlimit, systrace)],
+        [  --with-sandbox=style    Specify privilege separation sandbox (no, darwin, rlimit, systrace, seccomp_filter)],
         [
                 if test "x$withval" = "xyes" ; then
                         sandbox_arg=""
@@ -2541,6 +2586,23 @@ elif test "x$sandbox_arg" = "xdarwin" || \
                 AC_MSG_ERROR([Darwin seatbelt sandbox requires sandbox.h and sandbox_init function])
         SANDBOX_STYLE="darwin"
         AC_DEFINE([SANDBOX_DARWIN], [1], [Sandbox using Darwin sandbox_init(3)])
+elif test "x$sandbox_arg" = "xseccomp_filter" || \
+     ( test -z "$sandbox_arg" && \
+       test "x$have_seccomp_filter" == "x1" && \
+       test "x$ac_cv_header_linux_audit_h" = "xyes" && \
+       test "x$have_seccomp_audit_arch" = "x1" && \
+       test "x$have_linux_no_new_privs" = "x1" && \
+       test "x$ac_cv_func_prctl" = "xyes" ) ; then
+        test "x$have_seccomp_audit_arch" != "x1" && \
+                AC_MSG_ERROR([seccomp_filter sandbox not supported on $host])
+        test "x$have_linux_no_new_privs" != "x1" && \
+                AC_MSG_ERROR([seccomp_filter sandbox requires PR_SET_NO_NEW_PRIVS])
+        test "x$have_seccomp_filter" != "x1" && \
+                AC_MSG_ERROR([seccomp_filter sandbox requires seccomp headers])
+        test "x$ac_cv_func_prctl" != "xyes" && \
+                AC_MSG_ERROR([seccomp_filter sandbox requires prctl function])
+        SANDBOX_STYLE="seccomp_filter"
+        AC_DEFINE([SANDBOX_SECCOMP_FILTER], [1], [Sandbox using seccomp filter])
 elif test "x$sandbox_arg" = "xrlimit" || \
      ( test -z "$sandbox_arg" && test "x$ac_cv_func_setrlimit" = "xyes" ) ; then
         test "x$ac_cv_func_setrlimit" != "xyes" && \
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 <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 */
+
+#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/audit.h>
+#include <linux/filter.h>
+#include <linux/seccomp.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 */
+
+/* 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 */