kernel: add a helper to get an owning user namespace for a namespace

Return -EPERM if an owning user namespace is outside of a process
current user namespace.

v2: In a first version ns_get_owner returned ENOENT for init_user_ns.
    This special cases was removed from this version. There is nothing
    outside of init_user_ns, so we can return EPERM.
v3: rename ns->get_owner() to ns->owner(). get_* usually means that it
grabs a reference.

Acked-by: Serge Hallyn <serge@hallyn.com>
Signed-off-by: Andrei Vagin <avagin@openvz.org>
Signed-off-by: Eric W. Biederman <ebiederm@xmission.com>

9 files changed, 68 insertions, 0 deletions

diff --git a/fs/namespace.c b/fs/namespace.c
index 7bb2cda3bfef..fea56f310547 100644
--- a/fs/namespace.c
+++ b/fs/namespace.c
@@ -3348,10 +3348,16 @@ static int mntns_install(struct nsproxy *nsproxy, struct ns_common *ns)
         return 0;
 }
 
+static struct user_namespace *mntns_owner(struct ns_common *ns)
+{
+        return to_mnt_ns(ns)->user_ns;
+}
+
 const struct proc_ns_operations mntns_operations = {
         .name           = "mnt",
         .type           = CLONE_NEWNS,
         .get            = mntns_get,
         .put            = mntns_put,
         .install        = mntns_install,
+        .owner          = mntns_owner,
 };
diff --git a/include/linux/proc_ns.h b/include/linux/proc_ns.h
index de0e7719d4c5..ca85a4348ffc 100644
--- a/include/linux/proc_ns.h
+++ b/include/linux/proc_ns.h
@@ -18,6 +18,7 @@ struct proc_ns_operations {
         struct ns_common *(*get)(struct task_struct *task);
         void (*put)(struct ns_common *ns);
         int (*install)(struct nsproxy *nsproxy, struct ns_common *ns);
+        struct user_namespace *(*owner)(struct ns_common *ns);
 };
 
 extern const struct proc_ns_operations netns_operations;
diff --git a/include/linux/user_namespace.h b/include/linux/user_namespace.h
index 9217169c64cb..190cf0760815 100644
--- a/include/linux/user_namespace.h
+++ b/include/linux/user_namespace.h
@@ -73,6 +73,8 @@ extern ssize_t proc_setgroups_write(struct file *, const char __user *, size_t,
 extern int proc_setgroups_show(struct seq_file *m, void *v);
 extern bool userns_may_setgroups(const struct user_namespace *ns);
 extern bool current_in_userns(const struct user_namespace *target_ns);
+
+struct ns_common *ns_get_owner(struct ns_common *ns);
 #else
 
 static inline struct user_namespace *get_user_ns(struct user_namespace *ns)
@@ -106,6 +108,11 @@ static inline bool current_in_userns(const struct user_namespace *target_ns)
 {
         return true;
 }
+
+static inline struct ns_common *ns_get_owner(struct ns_common *ns)
+{
+        return ERR_PTR(-EPERM);
+}
 #endif
 
 #endif /* _LINUX_USER_H */
diff --git a/ipc/namespace.c b/ipc/namespace.c
index d87e6baa1323..578d93be619d 100644
--- a/ipc/namespace.c
+++ b/ipc/namespace.c
@@ -165,10 +165,16 @@ static int ipcns_install(struct nsproxy *nsproxy, struct ns_common *new)
         return 0;
 }
 
+static struct user_namespace *ipcns_owner(struct ns_common *ns)
+{
+        return to_ipc_ns(ns)->user_ns;
+}
+
 const struct proc_ns_operations ipcns_operations = {
         .name           = "ipc",
         .type           = CLONE_NEWIPC,
         .get            = ipcns_get,
         .put            = ipcns_put,
         .install        = ipcns_install,
+        .owner          = ipcns_owner,
 };
diff --git a/kernel/cgroup.c b/kernel/cgroup.c
index d1c51b7f5221..86b0e8b16426 100644
--- a/kernel/cgroup.c
+++ b/kernel/cgroup.c
@@ -6403,12 +6403,18 @@ static void cgroupns_put(struct ns_common *ns)
         put_cgroup_ns(to_cg_ns(ns));
 }
 
+static struct user_namespace *cgroupns_owner(struct ns_common *ns)
+{
+        return to_cg_ns(ns)->user_ns;
+}
+
 const struct proc_ns_operations cgroupns_operations = {
         .name           = "cgroup",
         .type           = CLONE_NEWCGROUP,
         .get            = cgroupns_get,
         .put            = cgroupns_put,
         .install        = cgroupns_install,
+        .owner          = cgroupns_owner,
 };
 
 static __init int cgroup_namespaces_init(void)
diff --git a/kernel/pid_namespace.c b/kernel/pid_namespace.c
index a65ba137fd15..c02d744225e1 100644
--- a/kernel/pid_namespace.c
+++ b/kernel/pid_namespace.c
@@ -388,12 +388,18 @@ static int pidns_install(struct nsproxy *nsproxy, struct ns_common *ns)
         return 0;
 }
 
+static struct user_namespace *pidns_owner(struct ns_common *ns)
+{
+        return to_pid_ns(ns)->user_ns;
+}
+
 const struct proc_ns_operations pidns_operations = {
         .name           = "pid",
         .type           = CLONE_NEWPID,
         .get            = pidns_get,
         .put            = pidns_put,
         .install        = pidns_install,
+        .owner          = pidns_owner,
 };
 
 static __init int pid_namespaces_init(void)
diff --git a/kernel/user_namespace.c b/kernel/user_namespace.c
index 68f594212759..0ef683a03c20 100644
--- a/kernel/user_namespace.c
+++ b/kernel/user_namespace.c
@@ -1004,12 +1004,36 @@ 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)
+{
+        struct user_namespace *my_user_ns = current_user_ns();
+        struct user_namespace *owner, *p;
+
+        /* See if the owner is in the current user namespace */
+        owner = p = ns->ops->owner(ns);
+        for (;;) {
+                if (!p)
+                        return ERR_PTR(-EPERM);
+                if (p == my_user_ns)
+                        break;
+                p = p->parent;
+        }
+
+        return &get_user_ns(owner)->ns;
+}
+
+static struct user_namespace *userns_owner(struct ns_common *ns)
+{
+        return to_user_ns(ns)->parent;
+}
+
 const struct proc_ns_operations userns_operations = {
         .name           = "user",
         .type           = CLONE_NEWUSER,
         .get            = userns_get,
         .put            = userns_put,
         .install        = userns_install,
+        .owner          = userns_owner,
 };
 
 static __init int user_namespaces_init(void)
diff --git a/kernel/utsname.c b/kernel/utsname.c
index 831ea7108232..e1211a8a5c18 100644
--- a/kernel/utsname.c
+++ b/kernel/utsname.c
@@ -130,10 +130,16 @@ static int utsns_install(struct nsproxy *nsproxy, struct ns_common *new)
         return 0;
 }
 
+static struct user_namespace *utsns_owner(struct ns_common *ns)
+{
+        return to_uts_ns(ns)->user_ns;
+}
+
 const struct proc_ns_operations utsns_operations = {
         .name           = "uts",
         .type           = CLONE_NEWUTS,
         .get            = utsns_get,
         .put            = utsns_put,
         .install        = utsns_install,
+        .owner          = utsns_owner,
 };
diff --git a/net/core/net_namespace.c b/net/core/net_namespace.c
index 2c2eb1b629b1..861efa34f08c 100644
--- a/net/core/net_namespace.c
+++ b/net/core/net_namespace.c
@@ -996,11 +996,17 @@ static int netns_install(struct nsproxy *nsproxy, struct ns_common *ns)
         return 0;
 }
 
+static struct user_namespace *netns_owner(struct ns_common *ns)
+{
+        return to_net_ns(ns)->user_ns;
+}
+
 const struct proc_ns_operations netns_operations = {
         .name           = "net",
         .type           = CLONE_NEWNET,
         .get            = netns_get,
         .put            = netns_put,
         .install        = netns_install,
+        .owner          = netns_owner,
 };
 #endif