- djm@cvs.openbsd.org 2011/06/22 21:57:01

     [servconf.c servconf.h sshd.c sshd_config.5 sandbox-rlimit.c]
     [sandbox-systrace.c sandbox.h configure.ac Makefile.in]
     introduce sandboxing of the pre-auth privsep child using systrace(4).

     This introduces a new "UsePrivilegeSeparation=sandbox" option for
     sshd_config that applies mandatory restrictions on the syscalls the
     privsep child can perform. This prevents a compromised privsep child
     from being used to attack other hosts (by opening sockets and proxying)
     or probing local kernel attack surface.

     The sandbox is implemented using systrace(4) in unsupervised "fast-path"
     mode, where a list of permitted syscalls is supplied. Any syscall not
     on the list results in SIGKILL being sent to the privsep child. Note
     that this requires a kernel with the new SYSTR_POLICY_KILL option.

     UsePrivilegeSeparation=sandbox will become the default in the future
     so please start testing it now.

     feedback dtucker@; ok markus@

1 files changed, 92 insertions, 0 deletions

diff --git a/sandbox-rlimit.c b/sandbox-rlimit.c
new file mode 100644
index 000000000..4d832fc3d
--- /dev/null
+++ b/sandbox-rlimit.c
@@ -0,0 +1,92 @@
+/*
+ * Copyright (c) 2011 Damien Miller <djm@mindrot.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.
+ */
+
+#include "includes.h"
+
+#ifdef SANDBOX_RLIMIT
+
+#include <sys/types.h>
+#include <sys/param.h>
+#include <sys/time.h>
+#include <sys/resource.h>
+
+#include <errno.h>
+#include <stdarg.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+#include <unistd.h>
+
+#include "log.h"
+#include "sandbox.h"
+#include "xmalloc.h"
+
+/* Minimal sandbox that sets zero nfiles, nprocs and filesize rlimits */
+
+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 rlimit sandbox", __func__);
+        box = xcalloc(1, sizeof(*box));
+        box->child_pid = 0;
+
+        return box;
+}
+
+void
+ssh_sandbox_child(struct ssh_sandbox *box)
+{
+        struct rlimit rl_zero;
+
+        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));
+#ifdef HAVE_RLIMIT_NPROC
+        if (setrlimit(RLIMIT_NPROC, &rl_zero) == -1)
+                fatal("%s: setrlimit(RLIMIT_NPROC, { 0, 0 }): %s",
+                        __func__, strerror(errno));
+#endif
+}
+
+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_RLIMIT */