From 69ff1df952eebf0489b775a60ede094eaf596a05 Mon Sep 17 00:00:00 2001 From: Damien Miller Date: Thu, 23 Jun 2011 08:30:03 +1000 Subject: - 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@ --- sandbox-systrace.c | 187 +++++++++++++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 187 insertions(+) create mode 100644 sandbox-systrace.c (limited to 'sandbox-systrace.c') diff --git a/sandbox-systrace.c b/sandbox-systrace.c new file mode 100644 index 000000000..5d0b7fb86 --- /dev/null +++ b/sandbox-systrace.c @@ -0,0 +1,187 @@ +/* + * Copyright (c) 2011 Damien Miller + * + * 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_SYSTRACE + +#include +#include +#include +#include +#include + +#include + +#include +#include +#include +#include +#include +#include +#include +#include + +#include "atomicio.h" +#include "log.h" +#include "sandbox.h" +#include "xmalloc.h" + +static const int preauth_policy[] = { + SYS___sysctl, + SYS_close, + SYS_exit, + SYS_getpid, + SYS_gettimeofday, + SYS_madvise, + SYS_mmap, + SYS_mprotect, + SYS_poll, + SYS_munmap, + SYS_read, + SYS_select, + SYS_sigprocmask, + SYS_write, + -1 +}; + +struct ssh_sandbox { + int child_sock; + int parent_sock; + int systrace_fd; + pid_t child_pid; + struct systrace_policy policy; +}; + +struct ssh_sandbox * +ssh_sandbox_init(void) +{ + struct ssh_sandbox *box; + int s[2]; + + debug3("%s: preparing systrace sandbox", __func__); + box = xcalloc(1, sizeof(*box)); + if (socketpair(AF_UNIX, SOCK_STREAM, 0, s) == -1) + fatal("%s: socketpair: %s", __func__, strerror(errno)); + box->child_sock = s[0]; + box->parent_sock = s[1]; + box->systrace_fd = -1; + box->child_pid = 0; + + return box; +} + +void +ssh_sandbox_child(struct ssh_sandbox *box) +{ + char whatever = 0; + + close(box->parent_sock); + /* Signal parent that we are ready */ + debug3("%s: ready", __func__); + if (atomicio(vwrite, box->child_sock, &whatever, 1) != 1) + fatal("%s: write: %s", __func__, strerror(errno)); + /* Wait for parent to signal for us to go */ + if (atomicio(read, box->child_sock, &whatever, 1) != 1) + fatal("%s: read: %s", __func__, strerror(errno)); + debug3("%s: started", __func__); + close(box->child_sock); +} + +static void +ssh_sandbox_parent(struct ssh_sandbox *box, pid_t child_pid, + const int *allowed_syscalls) +{ + int dev_systrace, i, j, found; + char whatever = 0; + + debug3("%s: wait for child %ld", __func__, (long)child_pid); + box->child_pid = child_pid; + close(box->child_sock); + /* Wait for child to signal that it is ready */ + if (atomicio(read, box->parent_sock, &whatever, 1) != 1) + fatal("%s: read: %s", __func__, strerror(errno)); + debug3("%s: child %ld ready", __func__, (long)child_pid); + + /* Set up systracing of child */ + if ((dev_systrace = open("/dev/systrace", O_RDONLY)) == -1) + fatal("%s: open(\"/dev/systrace\"): %s", __func__, + strerror(errno)); + if (ioctl(dev_systrace, STRIOCCLONE, &box->systrace_fd) == -1) + fatal("%s: ioctl(STRIOCCLONE, %d): %s", __func__, + dev_systrace, strerror(errno)); + close(dev_systrace); + debug3("%s: systrace attach, fd=%d", __func__, box->systrace_fd); + if (ioctl(box->systrace_fd, STRIOCATTACH, &child_pid) == -1) + fatal("%s: ioctl(%d, STRIOCATTACH, %d): %s", __func__, + box->systrace_fd, child_pid, strerror(errno)); + + /* Allocate and assign policy */ + bzero(&box->policy, sizeof(box->policy)); + box->policy.strp_op = SYSTR_POLICY_NEW; + box->policy.strp_maxents = SYS_MAXSYSCALL; + if (ioctl(box->systrace_fd, STRIOCPOLICY, &box->policy) == -1) + fatal("%s: ioctl(%d, STRIOCPOLICY (new)): %s", __func__, + box->systrace_fd, strerror(errno)); + + box->policy.strp_op = SYSTR_POLICY_ASSIGN; + box->policy.strp_pid = box->child_pid; + if (ioctl(box->systrace_fd, STRIOCPOLICY, &box->policy) == -1) + fatal("%s: ioctl(%d, STRIOCPOLICY (assign)): %s", + __func__, box->systrace_fd, strerror(errno)); + + /* Set per-syscall policy */ + for (i = 0; i < SYS_MAXSYSCALL; i++) { + for (j = found = 0; allowed_syscalls[j] != -1 && !found; j++) { + if (allowed_syscalls[j] == i) + found = 1; + } + box->policy.strp_op = SYSTR_POLICY_MODIFY; + box->policy.strp_code = i; + box->policy.strp_policy = found ? + SYSTR_POLICY_PERMIT : SYSTR_POLICY_KILL; + if (found) + debug3("%s: policy: enable syscall %d", __func__, i); + if (ioctl(box->systrace_fd, STRIOCPOLICY, + &box->policy) == -1) + fatal("%s: ioctl(%d, STRIOCPOLICY (modify)): %s", + __func__, box->systrace_fd, strerror(errno)); + } + + /* Signal the child to start running */ + debug3("%s: start child %ld", __func__, (long)child_pid); + if (atomicio(vwrite, box->parent_sock, &whatever, 1) != 1) + fatal("%s: write: %s", __func__, strerror(errno)); + close(box->parent_sock); +} + +void +ssh_sandbox_parent_finish(struct ssh_sandbox *box) +{ + /* Closing this before the child exits will terminate it */ + close(box->systrace_fd); + + free(box); + debug3("%s: finished", __func__); +} + +void +ssh_sandbox_parent_preauth(struct ssh_sandbox *box, pid_t child_pid) +{ + ssh_sandbox_parent(box, child_pid, preauth_policy); +} + +#endif /* SANDBOX_SYSTRACE */ -- cgit v1.2.3