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userns,pidns: Verify the userns for new pid namespaces

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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: 49f4d8b93c ("pidns: Capture the user namespace and filter ns_last_pid")
Signed-off-by: "Eric W. Biederman" <ebiederm@xmission.com>
This commit is contained in:
Eric W. Biederman 2017-04-29 14:12:15 -05:00
parent 5771a8c088
commit a2b426267c
3 changed files with 24 additions and 9 deletions
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9
include/linux/user_namespace.h
View file

@ -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;