On 29.04.2017 22:25, Eric W. Biederman wrote:
>
> It is pointless and confusing to allow a pid namespace hierarchy and
> the user namespace hierarchy to get out of sync. The owner of a child
> pid namespace should be the owner of the parent pid namespace or
> a descendant of the owner of the parent pid namespace.
>
> Otherwise it is possible to construct scenarios where it is legal to
> do something in a parent pid namespace but in a child pid namespace.
>
> It requires use of setns into a pid namespace (but not into a user
> namespace) to create such a scenario.
>
> Add the function in_userns to help in making this determination.
>
> Signed-off-by: "Eric W. Biederman" <ebiederm@xxxxxxxxxxxx>
> ---
>
> While review a patch from Kiril Tkhai I realized we were missing this
> sanity check....
>
> include/linux/user_namespace.h | 8 +++++++-
> kernel/pid_namespace.c | 4 ++++
> kernel/user_namespace.c | 18 ++++++++++++------
> 3 files changed, 23 insertions(+), 7 deletions(-)
>
> diff --git a/include/linux/user_namespace.h b/include/linux/user_namespace.h
> index 32354b4b4b2b..497ed50004db 100644
> --- a/include/linux/user_namespace.h
> +++ b/include/linux/user_namespace.h
> @@ -112,8 +112,9 @@ extern ssize_t proc_projid_map_write(struct file *, const char __user *, size_t,
> extern ssize_t proc_setgroups_write(struct file *, const char __user *, size_t, loff_t *);
> extern int proc_setgroups_show(struct seq_file *m, void *v);
> extern bool userns_may_setgroups(const struct user_namespace *ns);
> +extern bool in_userns(const struct user_namespace *ancestor,
> + const struct user_namespace *child);
> extern bool current_in_userns(const struct user_namespace *target_ns);
> -
> struct ns_common *ns_get_owner(struct ns_common *ns);
> #else
>
> @@ -144,6 +145,11 @@ static inline bool userns_may_setgroups(const struct user_namespace *ns)
> return true;
> }
>
> +static inline bool in_userns(const struct user_namespace *target_ns)
> +{
> + return true;
> +}
> +
> static inline bool current_in_userns(const struct user_namespace *target_ns)
> {
> return true;
> diff --git a/kernel/pid_namespace.c b/kernel/pid_namespace.c
> index de461aa0bf9a..749147f5a613 100644
> --- a/kernel/pid_namespace.c
> +++ b/kernel/pid_namespace.c
> @@ -101,6 +101,10 @@ static struct pid_namespace *create_pid_namespace(struct user_namespace *user_ns
> int i;
> int err;
>
> + err = -EINVAL;
> + if (!in_userns(parent_pid_ns->user_ns, user_ns))
> + goto out;
> +
> err = -ENOSPC;
> if (level > MAX_PID_NS_LEVEL)
> goto out;
> diff --git a/kernel/user_namespace.c b/kernel/user_namespace.c
> index 2f735cbe05e8..7d8658fbabc8 100644
> --- a/kernel/user_namespace.c
> +++ b/kernel/user_namespace.c
> @@ -986,19 +986,25 @@ bool userns_may_setgroups(const struct user_namespace *ns)
> }
>
> /*
> - * Returns true if @ns is the same namespace as or a descendant of
> - * @target_ns.
> + * Returns true if @child is the same namespace or a descendant of
> + * @ancestor.
> */
> -bool current_in_userns(const struct user_namespace *target_ns)
> +bool in_userns(const struct user_namespace *ancestor,
> + const struct user_namespace *child)
> {
> - struct user_namespace *ns;
> - for (ns = current_user_ns(); ns; ns = ns->parent) {
> - if (ns == target_ns)
> + const struct user_namespace *ns;
> + for (ns = child; ns; ns = ns->parent) {
> + if (ns == ancestor)
> return true;
> }
> return false;
> }
We have user_namespace::level, so it's possible to stop iterations earlier
and save some cpu cycles:
for (ns = child; ns->level >= ancestor->level; ns = ns->parent)
;
return (ns == ancestor);
>
> +bool current_in_userns(const struct user_namespace *target_ns)
> +{
> + return in_userns(target_ns, current_user_ns());
> +}
> +
> static inline struct user_namespace *to_user_ns(struct ns_common *ns)
> {
> return container_of(ns, struct user_namespace, ns);
>
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