Add support for SELinux RBAC. Sudoers entries may specify a role and type.

There are also role and type defaults that may be used.  To make sure a
transition occurs, when using RBAC commands are executed via the new sesh
binary.  Based on initial changes from Dan Walsh.

sesh.c

@@ -0,0 +1,60 @@
+/*
+ * Copyright (c) 2008 Todd C. Miller <Todd.Miller@courtesan.com>
+ *
+ * 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.
+ * OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF
+ * ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+ */
+
+#include <config.h>
+
+#include <sys/types.h>
+#include <err.h>
+#include <errno.h>
+#include <limits.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+#include <unistd.h>
+
+#include "compat.h"
+
+#ifndef lint
+__unused static const char rcsid[] = "$Sudo$";
+#endif /* lint */
+
+int
+main (int argc, char **argv)
+{
+    char *cp, *cmnd;
+
+    if (argc < 2)
+	errx(EXIT_FAILURE, "requires at least one argument");
+
+    /* Shift argv and make a copy of the command to execute. */
+    argv++;
+    argc--;
+    cmnd = strdup(argv[0]);
+    if (cmnd == NULL)
+	err(EXIT_FAILURE, NULL);
+
+    /* If invoked as a login shell, modify argv[0] accordingly. */
+    if (argv[0][0] == '-') {
+	if ((cp = strrchr(argv[0], '/')) == NULL)
+	    cp = argv[0];
+	*cp = '-';
+    }
+    execv(cmnd, argv);
+    warn("unable to execute %s", argv[0]);
+    _exit(EXIT_FAILURE);
+}