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Commit a2b42626 authored by Eric W. Biederman's avatar Eric W. Biederman
Browse files

userns,pidns: Verify the userns for new pid namespaces 



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 a process has a
capability over a parent pid namespace but does not have the
capability over a child pid namespace.  Which confusingly makes
permission checks non-transitive.

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.

v2: Optimized in_userns by using level as suggested
    by: Kirill Tkhai <ktkhai@virtuozzo.com>

Ref: 49f4d8b9 ("pidns: Capture the user namespace and filter ns_last_pid")
Signed-off-by: default avatar"Eric W. Biederman" <ebiederm@xmission.com>
parent 5771a8c0

include/linux/user_namespace.h

+8 −1
Original line number Diff line number Diff line
@@ -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 +145,12 @@ static inline bool userns_may_setgroups(const struct user_namespace *ns) 
	return true;

}



static inline bool in_userns(const struct user_namespace *ancestor,

			     const struct user_namespace *child)

{

	return true;

}



static inline bool current_in_userns(const struct user_namespace *target_ns)

{

	return true;

kernel/pid_namespace.c

+4 −0
Original line number Diff line number Diff line
@@ -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;

kernel/user_namespace.c

+12 −8
Original line number Diff line number Diff line
@@ -986,17 +986,21 @@ 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)

			return true;

	const struct user_namespace *ns;

	for (ns = child; ns->level > ancestor->level; ns = ns->parent)

		;

	return (ns == ancestor);

}

	return false;



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)