lguest: --username and --chroot options

I've attached a patch which implements dropping to privileges
and chrooting to a directory.

Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>

diff --git a/Documentation/lguest/lguest.c b/Documentation/lguest/lguest.c
index dc73bc54cc4e4cacb57fcb72289f88f5d99ef7e0..f64b85bcd6d42b228d6dd0de6262f5ff896b8697 100644 (file)
--- a/Documentation/lguest/lguest.c
+++ b/Documentation/lguest/lguest.c
@@ -39,6 +39,9 @@
 #include <limits.h>
 #include <stddef.h>
 #include <signal.h>
+#include <pwd.h>
+#include <grp.h>
+
 #include <linux/virtio_config.h>
 #include <linux/virtio_net.h>
 #include <linux/virtio_blk.h>
@@ -1872,6 +1875,8 @@ static struct option opts[] = {
        { "block", 1, NULL, 'b' },
        { "rng", 0, NULL, 'r' },
        { "initrd", 1, NULL, 'i' },
+       { "username", 1, NULL, 'u' },
+       { "chroot", 1, NULL, 'c' },
        { NULL },
 };
 static void usage(void)
@@ -1894,6 +1899,12 @@ int main(int argc, char *argv[])
        /* If they specify an initrd file to load. */
        const char *initrd_name = NULL;
 
+       /* Password structure for initgroups/setres[gu]id */
+       struct passwd *user_details = NULL;
+
+       /* Directory to chroot to */
+       char *chroot_path = NULL;
+
        /* Save the args: we "reboot" by execing ourselves again. */
        main_args = argv;
 
@@ -1950,6 +1961,14 @@ int main(int argc, char *argv[])
                case 'i':
                        initrd_name = optarg;
                        break;
+               case 'u':
+                       user_details = getpwnam(optarg);
+                       if (!user_details)
+                               err(1, "getpwnam failed, incorrect username?");
+                       break;
+               case 'c':
+                       chroot_path = optarg;
+                       break;
                default:
                        warnx("Unknown argument %s", argv[optind]);
                        usage();
@@ -2021,6 +2040,37 @@ int main(int argc, char *argv[])
        /* If we exit via err(), this kills all the threads, restores tty. */
        atexit(cleanup_devices);
 
+       /* If requested, chroot to a directory */
+       if (chroot_path) {
+               if (chroot(chroot_path) != 0)
+                       err(1, "chroot(\"%s\") failed", chroot_path);
+
+               if (chdir("/") != 0)
+                       err(1, "chdir(\"/\") failed");
+
+               verbose("chroot done\n");
+       }
+
+       /* If requested, drop privileges */
+       if (user_details) {
+               uid_t u;
+               gid_t g;
+
+               u = user_details->pw_uid;
+               g = user_details->pw_gid;
+
+               if (initgroups(user_details->pw_name, g) != 0)
+                       err(1, "initgroups failed");
+
+               if (setresgid(g, g, g) != 0)
+                       err(1, "setresgid failed");
+
+               if (setresuid(u, u, u) != 0)
+                       err(1, "setresuid failed");
+
+               verbose("Dropping privileges completed\n");
+       }
+
        /* Finally, run the Guest.  This doesn't return. */
        run_guest();
 }