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>

1 files changed, 50 insertions, 0 deletions

diff --git a/Documentation/lguest/lguest.c b/Documentation/lguest/lguest.c
index dc73bc54cc4..f64b85bcd6d 100644
--- 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();
 }