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Subject[PATCH 2/5] kernel: add a helper to get an owning user namespace for a namespace
Date
Return -EPERM if an owning user namespace is outside of a process
current user namespace.

Signed-off-by: Andrey Vagin <avagin@openvz.org>
---
include/linux/user_namespace.h | 7 +++++++
kernel/user_namespace.c | 24 ++++++++++++++++++++++++
2 files changed, 31 insertions(+)

diff --git a/include/linux/user_namespace.h b/include/linux/user_namespace.h
index a941b44..e416b76 100644
--- a/include/linux/user_namespace.h
+++ b/include/linux/user_namespace.h
@@ -76,6 +76,8 @@ 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);
+
+struct ns_common *ns_get_owner(struct ns_common *ns);
#else

static inline struct user_namespace *get_user_ns(struct user_namespace *ns)
@@ -104,6 +106,11 @@ static inline bool userns_may_setgroups(const struct user_namespace *ns)
{
return true;
}
+
+static inline struct ns_common *ns_get_owner(struct ns_common *ns)
+{
+ return ERR_PTR(-ENOENT);
+}
#endif

#endif /* _LINUX_USER_H */
diff --git a/kernel/user_namespace.c b/kernel/user_namespace.c
index a5bc78c..6382e5e 100644
--- a/kernel/user_namespace.c
+++ b/kernel/user_namespace.c
@@ -994,6 +994,30 @@ static int userns_install(struct nsproxy *nsproxy, struct ns_common *ns)
return commit_creds(cred);
}

+struct ns_common *ns_get_owner(struct ns_common *ns)
+{
+ const struct cred *cred = current_cred();
+ struct user_namespace *user_ns, *p;
+
+ user_ns = p = ns->user_ns;
+ if (user_ns == NULL) { /* ns is init_user_ns */
+ /* Unprivileged user should not know that it's init_user_ns. */
+ if (capable(CAP_SYS_ADMIN))
+ return ERR_PTR(-ENOENT);
+ return ERR_PTR(-EPERM);
+ }
+
+ for (;;) {
+ if (p == cred->user_ns)
+ break;
+ if (p == &init_user_ns)
+ return ERR_PTR(-EPERM);
+ p = p->parent;
+ }
+
+ return &get_user_ns(user_ns)->ns;
+}
+
const struct proc_ns_operations userns_operations = {
.name = "user",
.type = CLONE_NEWUSER,
--
2.5.5
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