fix chowning of tty and console uids

It needs to be done from the handler, not the container, since
the container may not have the rights.

Signed-off-by: Serge Hallyn <serge.hallyn@ubuntu.com>
Acked-by: Stéphane Graber <stgraber@ubuntu.com>

Changelog:
    Jul 22: remove hardcoded path for /bin/chown
    Jul 22: use new lxc-usernsexec

Conflicts:
	src/lxc/lxccontainer.c

src/lxc/conf.c

@@ -2858,7 +2858,7 @@ int lxc_map_ids(struct lxc_list *idmap, pid_t pid)
  * return the host uid to which the container root is mapped, or -1 on
  * error
  */
-int get_mapped_rootid(struct lxc_conf *conf)
+uid_t get_mapped_rootid(struct lxc_conf *conf)
 {
 	struct lxc_list *it;
 	struct id_map *map;
@@ -2869,9 +2869,9 @@ int get_mapped_rootid(struct lxc_conf *conf)
 			continue;
 		if (map->nsid != 0)
 			continue;
-		return map->hostid;
+		return (uid_t) map->hostid;
 	}
-	return -1;
+	return (uid_t)-1;
 }
 
 bool hostid_is_mapped(int id, struct lxc_conf *conf)
@@ -3020,88 +3020,80 @@ void lxc_delete_tty(struct lxc_tty_info *tty_info)
 }
 
 /*
- * given a host uid, return the ns uid if it is mapped.
+ * chown_mapped_root: for an unprivileged user with uid X to chown a dir
- * if it is not mapped, return the original host id.
+ * to subuid Y, he needs to run chown as root in a userns where
+ * nsid 0 is mapped to hostuid Y, and nsid Y is mapped to hostuid
+ * X.  That way, the container root is privileged with respect to
+ * hostuid X, allowing him to do the chown.
  */
-static int shiftid(struct lxc_conf *c, int uid, enum idtype w)
+int chown_mapped_root(char *path, struct lxc_conf *conf)
 {
-	struct lxc_list *iterator;
+	uid_t rootid;
-	struct id_map *map;
+	pid_t pid;
-	int low, high;
 
-	lxc_list_for_each(iterator, &c->id_map) {
+	if ((rootid = get_mapped_rootid(conf)) <= 0) {
-		map = iterator->elem;
+		ERROR("No mapping for container root");
-		if (map->idtype != w)
-			continue;
-
-		low = map->nsid;
-		high = map->nsid + map->range;
-		if (uid < low || uid >= high)
-			continue;
-
-		return uid - low + map->hostid;
-	}
-
-	return uid;
-}
-
-/*
- * Take a pathname for a file created on the host, and map the uid and gid
- * into the container if needed.  (Used for ttys)
- */
-static int uid_shift_file(char *path, struct lxc_conf *c)
-{
-	struct stat statbuf;
-	int newuid, newgid;
-
-	if (stat(path, &statbuf)) {
-		SYSERROR("stat(%s)", path);
 		return -1;
 	}
-
+	if (geteuid() == 0) {
-	newuid = shiftid(c, statbuf.st_uid, ID_TYPE_UID);
+		if (chown(path, rootid, -1) < 0) {
-	newgid = shiftid(c, statbuf.st_gid, ID_TYPE_GID);
+			ERROR("Error chowning %s", path);
-	if (newuid != statbuf.st_uid || newgid != statbuf.st_gid) {
-		DEBUG("chowning %s from %d:%d to %d:%d\n", path, (int)statbuf.st_uid, (int)statbuf.st_gid, newuid, newgid);
-		if (chown(path, newuid, newgid)) {
-			SYSERROR("chown(%s)", path);
 			return -1;
 		}
-	}
 		return 0;
 	}
+	pid = fork();
+	if (pid < 0) {
+		SYSERROR("Failed forking");
+		return -1;
+	}
+	if (!pid) {
+		int hostuid = geteuid(), ret;
+		char map1[100], map2[100];
+		char *args[] = {"lxc-usernsexec", "-m", map1, "-m", map2, "--", "chown",
+				 "0", path, NULL};
 
-int uid_shift_ttys(int pid, struct lxc_conf *conf)
+		// "b:0:rootid:1"
+		ret = snprintf(map1, 100, "b:0:%d:1", rootid);
+		if (ret < 0 || ret >= 100) {
+			ERROR("Error uid printing map string");
+			return -1;
+		}
+
+		// "b:hostuid:hostuid:1"
+		ret = snprintf(map2, 100, "b:%d:%d:1", hostuid, hostuid);
+		if (ret < 0 || ret >= 100) {
+			ERROR("Error uid printing map string");
+			return -1;
+		}
+
+		ret = execvp("lxc-usernsexec", args);
+		SYSERROR("Failed executing usernsexec");
+		exit(1);
+	}
+	return wait_for_pid(pid);
+}
+
+int ttys_shift_ids(struct lxc_conf *c)
 {
-	int i, ret;
+	int i;
-	struct lxc_tty_info *tty_info = &conf->tty_info;
-	char path[MAXPATHLEN];
-	char *ttydir = conf->ttydir;
 
-	if (!conf->rootfs.path)
+	if (lxc_list_empty(&c->id_map))
 		return 0;
-	/* first the console */
+
-	ret = snprintf(path, sizeof(path), "/proc/%d/root/dev/%s/console", pid, ttydir ? ttydir : "");
+	for (i = 0; i < c->tty_info.nbtty; i++) {
-	if (ret < 0 || ret >= sizeof(path)) {
+		struct lxc_pty_info *pty_info = &c->tty_info.pty_info[i];
-		ERROR("console path too long\n");
+
+		if (chown_mapped_root(pty_info->name, c) < 0) {
+			ERROR("Failed to chown %s", pty_info->name);
 			return -1;
 		}
-	if (uid_shift_file(path, conf)) {
-		DEBUG("Failed to chown the console %s.\n", path);
-		return -1;
 	}
-	for (i=0; i< tty_info->nbtty; i++) {
+
-		ret = snprintf(path, sizeof(path), "/proc/%d/root/dev/%s/tty%d",
+	if (chown_mapped_root(c->console.name, c) < 0) {
-			pid, ttydir ? ttydir : "", i + 1);
+		ERROR("Failed to chown %s", c->console.name);
-		if (ret < 0 || ret >= sizeof(path)) {
-			ERROR("pathname too long for ttys");
 		return -1;
 	}
-		if (uid_shift_file(path, conf)) {
-			DEBUG("Failed to chown pty %s.\n", path);
-			return -1;
-		}
-	}
 
 	return 0;
 }

src/lxc/conf.h

@@ -350,8 +350,6 @@ extern int lxc_clear_cgroups(struct lxc_conf *c, const char *key);
 extern int lxc_clear_mount_entries(struct lxc_conf *c);
 extern int lxc_clear_hooks(struct lxc_conf *c, const char *key);
 
-extern int uid_shift_ttys(int pid, struct lxc_conf *conf);
-
 /*
  * Configure the container from inside
  */
@@ -362,7 +360,9 @@ extern int lxc_setup(const char *name, struct lxc_conf *lxc_conf,
 
 extern void lxc_rename_phys_nics_on_shutdown(struct lxc_conf *conf);
 
-extern int get_mapped_rootid(struct lxc_conf *conf);
+extern uid_t get_mapped_rootid(struct lxc_conf *conf);
 extern int find_unmapped_nsuid(struct lxc_conf *conf);
 extern bool hostid_is_mapped(int id, struct lxc_conf *conf);
+extern int chown_mapped_root(char *path, struct lxc_conf *conf);
+extern int ttys_shift_ids(struct lxc_conf *c);
 #endif

src/lxc/lxccontainer.c

@@ -693,49 +693,6 @@ static bool create_container_dir(struct lxc_container *c)
 static const char *lxcapi_get_config_path(struct lxc_container *c);
 static bool lxcapi_set_config_item(struct lxc_container *c, const char *key, const char *v);
 
-/*
- * chown_mapped: for an unprivileged user with uid X to chown a dir
- * to subuid Y, he needs to run chown as root in a userns where
- * nsid 0 is mapped to hostuid Y, and nsid Y is mapped to hostuid
- * X.  That way, the container root is privileged with respect to
- * hostuid X, allowing him to do the chown.
- */
-static int chown_mapped(int nsrootid, char *path)
-{
-	if (nsrootid < 0)
-		return nsrootid;
-	pid_t pid = fork();
-	if (pid < 0) {
-		SYSERROR("Failed forking");
-		return -1;
-	}
-	if (!pid) {
-		int hostuid = geteuid(), ret;
-		char map1[100], map2[100];
-		char *args[] = {"lxc-usernsexec", "-m", map1, "-m", map2, "--", "chown",
-				 "0", path, NULL};
-
-		// "b:0:nsrootid:1"
-		ret = snprintf(map1, 100, "b:0:%d:1", nsrootid);
-		if (ret < 0 || ret >= 100) {
-			ERROR("Error uid printing map string");
-			return -1;
-		}
-
-		// "b:hostuid:hostuid:1"
-		ret = snprintf(map2, 100, "b:%d:%d:1", hostuid, hostuid);
-		if (ret < 0 || ret >= 100) {
-			ERROR("Error uid printing map string");
-			return -1;
-		}
-
-		ret = execvp("lxc-usernsexec", args);
-		SYSERROR("Failed executing lxc-usernsexec");
-		exit(1);
-	}
-	return wait_for_pid(pid);
-}
-
 /*
  * do_bdev_create: thin wrapper around bdev_create().  Like bdev_create(),
  * it returns a mounted bdev on success, NULL on error.
@@ -768,15 +725,8 @@ static struct bdev *do_bdev_create(struct lxc_container *c, const char *type,
 	 * target uidmap */
 
 	if (geteuid() != 0) {
-		int rootid;
+		if (chown_mapped_root(bdev->dest, c->lxc_conf) < 0) {
-		if ((rootid = get_mapped_rootid(c->lxc_conf)) <= 0) {
+			ERROR("Error chowning %s to container root\n", bdev->dest);
-			ERROR("No mapping for container root");
-			bdev_put(bdev);
-			return NULL;
-		}
-		ret = chown_mapped(rootid, bdev->dest);
-		if (ret < 0) {
-			ERROR("Error chowning %s to %d\n", bdev->dest, rootid);
 			bdev_put(bdev);
 			return NULL;
 		}

src/lxc/start.c

@@ -353,6 +353,11 @@ struct lxc_handler *lxc_init(const char *name, struct lxc_conf *conf, const char
 		goto out_restore_sigmask;
 	}
 
+	if (ttys_shift_ids(conf) < 0) {
+		ERROR("Failed to shift tty into container");
+		goto out_restore_sigmask;
+	}
+
 	INFO("'%s' is initialized", name);
 	return handler;
 
@@ -784,11 +789,6 @@ int lxc_spawn(struct lxc_handler *handler)
 	if (detect_shared_rootfs())
 		umount2(handler->conf->rootfs.mount, MNT_DETACH);
 
-	/* If child is in a fresh user namespace, chown his ptys for
-	 * it */
-	if (uid_shift_ttys(handler->pid, handler->conf))
-		DEBUG("Failed to chown ptys.\n");
-
 	if (handler->ops->post_start(handler, handler->data))
 		goto out_abort;