[PATCH review 09/16] userns: Implent proc namespace operations

Eric W. Biederman
2012-11-19T15:13:49Z

This allows entering a user namespace, and the ability
to store a reference to a user namespace with a bind
mount.

Addition of missing userns_ns_put in userns_install
from Gao feng <gaofeng@cn.fujitsu.com>

Acked-by: Serge Hallyn <serge.hallyn@canonical.com>
Signed-off-by: "Eric W. Biederman" <ebiederm@xmission.com>
---
fs/proc/namespaces.c | 4 ++
include/linux/proc_fs.h | 1 +
kernel/user_namespace.c | 90 ++++++++++++++++++++++++++++++++++++++---------
3 files changed, 78 insertions(+), 17 deletions(-)

diff --git a/fs/proc/namespaces.c b/fs/proc/namespaces.c
index 2a17fd9..030250c 100644
--- a/fs/proc/namespaces.c
+++ b/fs/proc/namespaces.c
@@ -11,6 +11,7 @@
#include <net/net_namespace.h>
#include <linux/ipc_namespace.h>
#include <linux/pid_namespace.h>
+#include <linux/user_namespace.h>
#include "internal.h"

@@ -27,6 +28,9 @@ static const struct proc_ns_operations *ns_entries[] = {
#ifdef CONFIG_PID_NS
&pidns_operations,
#endif
+#ifdef CONFIG_USER_NS
+ &userns_operations,
+#endif
&mntns_operations,
};

diff --git a/include/linux/proc_fs.h b/include/linux/proc_fs.h
index 9014c04..3144781 100644
--- a/include/linux/proc_fs.h
+++ b/include/linux/proc_fs.h
@@ -258,6 +258,7 @@ extern const struct proc_ns_operations netns_operations;
extern const struct proc_ns_operations utsns_operations;
extern const struct proc_ns_operations ipcns_operations;
extern const struct proc_ns_operations pidns_operations;
+extern const struct proc_ns_operations userns_operations;
extern const struct proc_ns_operations mntns_operations;

union proc_op {
diff --git a/kernel/user_namespace.c b/kernel/user_namespace.c
index 49096d5..a946077 100644
--- a/kernel/user_namespace.c
+++ b/kernel/user_namespace.c
@@ -9,6 +9,7 @@
#include <linux/nsproxy.h>
#include <linux/slab.h>
#include <linux/user_namespace.h>
+#include <linux/proc_fs.h>
#include <linux/highuid.h>
#include <linux/cred.h>
#include <linux/securebits.h>
@@ -26,6 +27,24 @@ static struct kmem_cache *user_ns_cachep __read_mostly;
static bool new_idmap_permitted(struct user_namespace *ns, int cap_setid,
struct uid_gid_map *map);

+static void set_cred_user_ns(struct cred *cred, struct user_namespace *user_ns)
+{
+ /* Start with the same capabilities as init but useless for doing
+ * anything as the capabilities are bound to the new user namespace.
+ */
+ cred->securebits = SECUREBITS_DEFAULT;
+ cred->cap_inheritable = CAP_EMPTY_SET;
+ cred->cap_permitted = CAP_FULL_SET;
+ cred->cap_effective = CAP_FULL_SET;
+ cred->cap_bset = CAP_FULL_SET;
+#ifdef CONFIG_KEYS
+ key_put(cred->request_key_auth);
+ cred->request_key_auth = NULL;
+#endif
+ /* tgcred will be cleared in our caller bc CLONE_THREAD won't be set */
+ cred->user_ns = user_ns;
+}
+
/*
* Create a new user namespace, deriving the creator from the user in the
* passed credentials, and replacing that user with the new root user for the
@@ -53,27 +72,12 @@ int create_user_ns(struct cred *new)
return -ENOMEM;

kref_init(&ns->kref);
+ /* Leave the new->user_ns reference with the new user namespace. */
ns->parent = parent_ns;
ns->owner = owner;
ns->group = group;

- /* Start with the same capabilities as init but useless for doing
- * anything as the capabilities are bound to the new user namespace.
- */
- new->securebits = SECUREBITS_DEFAULT;
- new->cap_inheritable = CAP_EMPTY_SET;
- new->cap_permitted = CAP_FULL_SET;
- new->cap_effective = CAP_FULL_SET;
- new->cap_bset = CAP_FULL_SET;
-#ifdef CONFIG_KEYS
- key_put(new->request_key_auth);
- new->request_key_auth = NULL;
-#endif
- /* tgcred will be cleared in our caller bc CLONE_THREAD won't be set */
-
- /* Leave the new->user_ns reference with the new user namespace. */
- /* Leave the reference to our user_ns with the new cred. */
- new->user_ns = ns;
+ set_cred_user_ns(new, ns);

return 0;
}
@@ -737,6 +741,58 @@ static bool new_idmap_permitted(struct user_namespace *ns, int cap_setid,
return false;
}

+static void *userns_get(struct task_struct *task)
+{
+ struct user_namespace *user_ns;
+
+ rcu_read_lock();
+ user_ns = get_user_ns(__task_cred(task)->user_ns);
+ rcu_read_unlock();
+
+ return user_ns;
+}
+
+static void userns_put(void *ns)
+{
+ put_user_ns(ns);
+}
+
+static int userns_install(struct nsproxy *nsproxy, void *ns)
+{
+ struct user_namespace *user_ns = ns;
+ struct cred *cred;
+
+ /* Don't allow gaining capabilities by reentering
+ * the same user namespace.
+ */
+ if (user_ns == current_user_ns())
+ return -EINVAL;
+
+ /* Threaded many not enter a different user namespace */
+ if (atomic_read(&current->mm->mm_users) > 1)
+ return -EINVAL;
+
+ if (!ns_capable(user_ns, CAP_SYS_ADMIN))
+ return -EPERM;
+
+ cred = prepare_creds();
+ if (!cred)
+ return -ENOMEM;
+
+ put_user_ns(cred->user_ns);
+ set_cred_user_ns(cred, get_user_ns(user_ns));
+
+ return commit_creds(cred);
+}
+
+const struct proc_ns_operations userns_operations = {
+ .name = "user",
+ .type = CLONE_NEWUSER,
+ .get = userns_get,
+ .put = userns_put,
+ .install = userns_install,
+};
+
static __init int user_namespaces_init(void)
{
user_ns_cachep = KMEM_CACHE(user_namespace, SLAB_PANIC);
--
1.7.5.4