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: 49f4d8b93ccf ("pidns: Capture the user namespace and filter ns_last_pid")
Signed-off-by: "Eric W. Biederman" <ebiederm@xmission.com>
diff --git a/include/linux/user_namespace.h b/include/linux/user_namespace.h
index 32354b4..4005877 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 +145,12 @@ 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;
diff --git a/kernel/pid_namespace.c b/kernel/pid_namespace.c
index 74a5a72..4918314 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 2f735cb..c490f1e 100644
--- a/kernel/user_namespace.c
+++ b/kernel/user_namespace.c
@@ -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 in_userns(const struct user_namespace *ancestor,
+ const struct user_namespace *child)
+{
+ const struct user_namespace *ns;
+ for (ns = child; ns->level > ancestor->level; ns = ns->parent)
+ ;
+ return (ns == ancestor);
+}
+
bool current_in_userns(const struct user_namespace *target_ns)
{
- struct user_namespace *ns;
- for (ns = current_user_ns(); ns; ns = ns->parent) {
- if (ns == target_ns)
- return true;
- }
- return false;
+ return in_userns(target_ns, current_user_ns());
}
static inline struct user_namespace *to_user_ns(struct ns_common *ns)