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Subject[PATCH v21 013/100] c/r: break out new_user_ns()
Date
From: Serge E. Hallyn <serue@us.ibm.com>

Break out the core function which checks privilege and (if
allowed) creates a new user namespace, with the passed-in
creating user_struct. Note that a user_namespace, unlike
other namespace pointers, is not stored in the nsproxy.
Rather it is purely a property of user_structs.

This will let us keep the task restore code simpler.

Cc: David Howells <dhowells@redhat.com>
Signed-off-by: Serge E. Hallyn <serue@us.ibm.com>
Acked-by: Oren Laadan <orenl@cs.columbia.edu>
---
include/linux/user_namespace.h | 8 ++++++
kernel/user_namespace.c | 53 ++++++++++++++++++++++++++++------------
2 files changed, 45 insertions(+), 16 deletions(-)

diff --git a/include/linux/user_namespace.h b/include/linux/user_namespace.h
index cc4f453..f6ea75d 100644
--- a/include/linux/user_namespace.h
+++ b/include/linux/user_namespace.h
@@ -20,6 +20,8 @@ extern struct user_namespace init_user_ns;

#ifdef CONFIG_USER_NS

+struct user_namespace *new_user_ns(struct user_struct *creator,
+ struct user_struct **newroot);
static inline struct user_namespace *get_user_ns(struct user_namespace *ns)
{
if (ns)
@@ -38,6 +40,12 @@ static inline void put_user_ns(struct user_namespace *ns)

#else

+static inline struct user_namespace *new_user_ns(struct user_struct *creator,
+ struct user_struct **newroot)
+{
+ return ERR_PTR(-EINVAL);
+}
+
static inline struct user_namespace *get_user_ns(struct user_namespace *ns)
{
return &init_user_ns;
diff --git a/kernel/user_namespace.c b/kernel/user_namespace.c
index 076c7c8..e624b0f 100644
--- a/kernel/user_namespace.c
+++ b/kernel/user_namespace.c
@@ -11,15 +11,8 @@
#include <linux/user_namespace.h>
#include <linux/cred.h>

-/*
- * 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
- * new namespace.
- *
- * This is called by copy_creds(), which will finish setting the target task's
- * credentials.
- */
-int create_user_ns(struct cred *new)
+static struct user_namespace *_new_user_ns(struct user_struct *creator,
+ struct user_struct **newroot)
{
struct user_namespace *ns;
struct user_struct *root_user;
@@ -27,7 +20,7 @@ int create_user_ns(struct cred *new)

ns = kmalloc(sizeof(struct user_namespace), GFP_KERNEL);
if (!ns)
- return -ENOMEM;
+ return ERR_PTR(-ENOMEM);

kref_init(&ns->kref);

@@ -38,12 +31,43 @@ int create_user_ns(struct cred *new)
root_user = alloc_uid(ns, 0);
if (!root_user) {
kfree(ns);
- return -ENOMEM;
+ return ERR_PTR(-ENOMEM);
}

/* set the new root user in the credentials under preparation */
- ns->creator = new->user;
- new->user = root_user;
+ ns->creator = creator;
+
+ /* alloc_uid() incremented the userns refcount. Just set it to 1 */
+ kref_set(&ns->kref, 1);
+
+ *newroot = root_user;
+ return ns;
+}
+
+struct user_namespace *new_user_ns(struct user_struct *creator,
+ struct user_struct **newroot)
+{
+ if (!capable(CAP_SYS_ADMIN))
+ return ERR_PTR(-EPERM);
+ return _new_user_ns(creator, newroot);
+}
+
+/*
+ * 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
+ * new namespace.
+ *
+ * This is called by copy_creds(), which will finish setting the target task's
+ * credentials.
+ */
+int create_user_ns(struct cred *new)
+{
+ struct user_namespace *ns;
+
+ ns = new_user_ns(new->user, &new->user);
+ if (IS_ERR(ns))
+ return PTR_ERR(ns);
+
new->uid = new->euid = new->suid = new->fsuid = 0;
new->gid = new->egid = new->sgid = new->fsgid = 0;
put_group_info(new->group_info);
@@ -54,9 +78,6 @@ int create_user_ns(struct cred *new)
#endif
/* tgcred will be cleared in our caller bc CLONE_THREAD won't be set */

- /* alloc_uid() incremented the userns refcount. Just set it to 1 */
- kref_set(&ns->kref, 1);
-
return 0;
}

--
1.6.3.3


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