Currently, creating a new user namespace does not reset the task's uid or gid. Since generally that is done as root because it requires CAP_SYS_ADMIN, and since the first uid in the new namespace is 0, one usually doesn't notice. However, if one does capset cap_sys_admin=ep ns_exec su - hallyn ns_exec -U /bin/sh id then one will see hallyn's userid, and all preexisting groups. With this patch, cloning a new user namespace will set the task's uid and gid to 0, and reset the group_info to the empty set assigned to init. Signed-off-by: Serge E. Hallyn <serue@xxxxxxxxxx> --- kernel/user_namespace.c | 14 ++++++++++++++ 1 files changed, 14 insertions(+), 0 deletions(-) diff --git a/kernel/user_namespace.c b/kernel/user_namespace.c index 0045dd0..39aea7b 100644 --- a/kernel/user_namespace.c +++ b/kernel/user_namespace.c @@ -11,6 +11,9 @@ #include <linux/slab.h> #include <linux/user_namespace.h> +/* defined in kernel/sys.c */ +extern struct group_info init_groups; + /* * Clone a new ns copying an original user ns, setting refcount to 1 * @old_ns: namespace to clone @@ -48,6 +51,17 @@ int create_new_userns(int flags, struct task_struct *tsk) put_user_ns(ns); task_switch_uid(tsk, ns->root_user); + tsk->uid = tsk->euid = tsk->suid = tsk->fsuid = 0; + tsk->gid = tsk->egid = tsk->sgid = tsk->fsgid = 0; + + /* this can't be safe for unshare, can it? it's safe + * for fork, though. I'm tempted to limit clone_newuser to + * fork only */ + task_lock(tsk); + put_group_info(tsk->group_info); + tsk->group_info = &init_groups; + get_group_info(tsk->group_info); + task_unlock(tsk); return 0; } -- 1.5.4.3 _______________________________________________ Containers mailing list Containers@xxxxxxxxxxxxxxxxxxxxxxxxxx https://lists.linux-foundation.org/mailman/listinfo/containers