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

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
...@@ -112,8 +112,9 @@ extern ssize_t proc_projid_map_write(struct file *, const char __user *, size_t, ...@@ -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 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 int proc_setgroups_show(struct seq_file *m, void *v);
extern bool userns_may_setgroups(const struct user_namespace *ns); 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); extern bool current_in_userns(const struct user_namespace *target_ns);
struct ns_common *ns_get_owner(struct ns_common *ns); struct ns_common *ns_get_owner(struct ns_common *ns);
#else #else
...@@ -144,6 +145,12 @@ static inline bool userns_may_setgroups(const struct user_namespace *ns) ...@@ -144,6 +145,12 @@ static inline bool userns_may_setgroups(const struct user_namespace *ns)
return true; 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) static inline bool current_in_userns(const struct user_namespace *target_ns)
{ {
return true; return true;
......
...@@ -101,6 +101,10 @@ static struct pid_namespace *create_pid_namespace(struct user_namespace *user_ns ...@@ -101,6 +101,10 @@ static struct pid_namespace *create_pid_namespace(struct user_namespace *user_ns
int i; int i;
int err; int err;
err = -EINVAL;
if (!in_userns(parent_pid_ns->user_ns, user_ns))
goto out;
err = -ENOSPC; err = -ENOSPC;
if (level > MAX_PID_NS_LEVEL) if (level > MAX_PID_NS_LEVEL)
goto out; goto out;
......
...@@ -986,17 +986,21 @@ bool userns_may_setgroups(const struct user_namespace *ns) ...@@ -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 * Returns true if @child is the same namespace or a descendant of
* @target_ns. * @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) bool current_in_userns(const struct user_namespace *target_ns)
{ {
struct user_namespace *ns; return in_userns(target_ns, current_user_ns());
for (ns = current_user_ns(); ns; ns = ns->parent) {
if (ns == target_ns)
return true;
}
return false;
} }
static inline struct user_namespace *to_user_ns(struct ns_common *ns) static inline struct user_namespace *to_user_ns(struct ns_common *ns)
......
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