- markus@cvs.openbsd.org 2012/06/30 14:35:09

[sandbox-systrace.c sshd.c]
     fix a during the load of the sandbox policies (child can still make
     the read-syscall and wait forever for systrace-answers) by replacing
     the read/write synchronisation with SIGSTOP/SIGCONT;
     report and help hshoexer@; ok djm@, dtucker@

ChangeLog

@@ -4,6 +4,12 @@
      [ssh_config.5 sshd_config.5]
      match the documented MAC order of preference to the actual one;
      ok dtucker@
+   - markus@cvs.openbsd.org 2012/06/30 14:35:09
+     [sandbox-systrace.c sshd.c]
+     fix a during the load of the sandbox policies (child can still make
+     the read-syscall and wait forever for systrace-answers) by replacing
+     the read/write synchronisation with SIGSTOP/SIGCONT;
+     report and help hshoexer@; ok djm@, dtucker@
 
 20120629
  - OpenBSD CVS Sync

sandbox-systrace.c

@@ -1,4 +1,4 @@
-/* $OpenBSD: sandbox-systrace.c,v 1.5 2012/06/26 11:02:30 dtucker Exp $ */
+/* $OpenBSD: sandbox-systrace.c,v 1.6 2012/06/30 14:35:09 markus Exp $ */
 /*
  * Copyright (c) 2011 Damien Miller <djm@mindrot.org>
  *
@@ -24,12 +24,14 @@
 #include <sys/ioctl.h>
 #include <sys/syscall.h>
 #include <sys/socket.h>
+#include <sys/wait.h>
 
 #include <dev/systrace.h>
 
 #include <errno.h>
 #include <fcntl.h>
 #include <limits.h>
+#include <signal.h>
 #include <stdarg.h>
 #include <stdio.h>
 #include <stdlib.h>
@@ -69,26 +71,21 @@ static const struct sandbox_policy preauth_policy[] = {
 };
 
 struct ssh_sandbox {
-	int child_sock;
-	int parent_sock;
 	int systrace_fd;
 	pid_t child_pid;
+	void (*osigchld)(int);
 };
 
 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;
+	box->osigchld = signal(SIGCHLD, SIG_IGN);
 
 	return box;
 }
@@ -96,35 +93,38 @@ ssh_sandbox_init(void)
 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)
+	signal(SIGCHLD, box->osigchld);
-		fatal("%s: write: %s", __func__, strerror(errno));
+	if (kill(getpid(), SIGSTOP) != 0)
-	/* Wait for parent to signal for us to go */
+		fatal("%s: kill(%d, SIGSTOP)", __func__, getpid());
-	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 struct sandbox_policy *allowed_syscalls)
 {
-	int dev_systrace, i, j, found;
+	int dev_systrace, i, j, found, status;
-	char whatever = 0;
+	pid_t pid;
 	struct systrace_policy policy;
 
+	/* Wait for the child to send itself a SIGSTOP */
 	debug3("%s: wait for child %ld", __func__, (long)child_pid);
+	do {
+		pid = waitpid(child_pid, &status, WUNTRACED);
+	} while (pid == -1 && errno == EINTR);
+	signal(SIGCHLD, box->osigchld);
+	if (!WIFSTOPPED(status)) {
+		if (WIFSIGNALED(status))
+			fatal("%s: child terminated with signal %d",
+			    __func__, WTERMSIG(status));
+		if (WIFEXITED(status))
+			fatal("%s: child exited with status %d",
+			    __func__, WEXITSTATUS(status));
+		fatal("%s: child not stopped", __func__);
+	}
+	debug3("%s: child %ld stopped", __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)
@@ -175,9 +175,8 @@ ssh_sandbox_parent(struct ssh_sandbox *box, pid_t child_pid,
 
 	/* Signal the child to start running */
 	debug3("%s: start child %ld", __func__, (long)child_pid);
-	if (atomicio(vwrite, box->parent_sock, &whatever, 1) != 1)
+	if (kill(box->child_pid, SIGCONT) != 0)
-		fatal("%s: write: %s", __func__, strerror(errno));
+		fatal("%s: kill(%d, SIGCONT)", __func__, box->child_pid);
-	close(box->parent_sock);
 }
 
 void

sshd.c

@@ -1,4 +1,4 @@
-/* $OpenBSD: sshd.c,v 1.391 2012/05/13 01:42:32 dtucker Exp $ */
+/* $OpenBSD: sshd.c,v 1.392 2012/06/30 14:35:09 markus Exp $ */
 /*
  * Author: Tatu Ylonen <ylo@cs.hut.fi>
  * Copyright (c) 1995 Tatu Ylonen <ylo@cs.hut.fi>, Espoo, Finland
@@ -643,9 +643,9 @@ privsep_preauth(Authctxt *authctxt)
 	} else if (pid != 0) {
 		debug2("Network child is on pid %ld", (long)pid);
 
+		pmonitor->m_pid = pid;
 		if (box != NULL)
 			ssh_sandbox_parent_preauth(box, pid);
-		pmonitor->m_pid = pid;
 		monitor_child_preauth(authctxt, pmonitor);
 
 		/* Sync memory */