user namespace: add the framework

Basically, it will allow a process to unshare its user_struct table,
resetting at the same time its own user_struct and all the associated
accounting.

A new root user (uid == 0) is added to the user namespace upon creation.
Such root users have full privileges and it seems that theses privileges
should be controlled through some means (process capabilities ?)

The unshare is not included in this patch.

Changes since [try #4]:
	- Updated get_user_ns and put_user_ns to accept NULL, and
	  get_user_ns to return the namespace.

Changes since [try #3]:
	- moved struct user_namespace to files user_namespace.{c,h}

Changes since [try #2]:
	- removed struct user_namespace* argument from find_user()

Changes since [try #1]:
	- removed struct user_namespace* argument from find_user()
	- added a root_user per user namespace

Signed-off-by: Cedric Le Goater <clg@fr.ibm.com>
Signed-off-by: Serge E. Hallyn <serue@us.ibm.com>
Acked-by: Pavel Emelianov <xemul@openvz.org>
Cc: Herbert Poetzl <herbert@13thfloor.at>
Cc: Kirill Korotaev <dev@sw.ru>
Cc: Eric W. Biederman <ebiederm@xmission.com>
Cc: Chris Wright <chrisw@sous-sol.org>
Cc: Stephen Smalley <sds@tycho.nsa.gov>
Cc: James Morris <jmorris@namei.org>
Cc: Andrew Morgan <agm@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 9 insertions, 9 deletions

diff --git a/kernel/user.c b/kernel/user.c
index 4869563080e9..98b82507797a 100644
--- a/kernel/user.c
+++ b/kernel/user.c
@@ -14,20 +14,19 @@
 #include <linux/bitops.h>
 #include <linux/key.h>
 #include <linux/interrupt.h>
+#include <linux/module.h>
+#include <linux/user_namespace.h>
 
 /*
  * UID task count cache, to get fast user lookup in "alloc_uid"
  * when changing user ID's (ie setuid() and friends).
  */
 
-#define UIDHASH_BITS (CONFIG_BASE_SMALL ? 3 : 8)
-#define UIDHASH_SZ              (1 << UIDHASH_BITS)
 #define UIDHASH_MASK            (UIDHASH_SZ - 1)
 #define __uidhashfn(uid)        (((uid >> UIDHASH_BITS) + uid) & UIDHASH_MASK)
-#define uidhashentry(uid)       (uidhash_table + __uidhashfn((uid)))
+#define uidhashentry(ns, uid)   ((ns)->uidhash_table + __uidhashfn((uid)))
 
 static struct kmem_cache *uid_cachep;
-static struct list_head uidhash_table[UIDHASH_SZ];
 
 /*
  * The uidhash_lock is mostly taken from process context, but it is
@@ -94,9 +93,10 @@ struct user_struct *find_user(uid_t uid)
 {
         struct user_struct *ret;
         unsigned long flags;
+        struct user_namespace *ns = current->nsproxy->user_ns;
 
         spin_lock_irqsave(&uidhash_lock, flags);
-        ret = uid_hash_find(uid, uidhashentry(uid));
+        ret = uid_hash_find(uid, uidhashentry(ns, uid));
         spin_unlock_irqrestore(&uidhash_lock, flags);
         return ret;
 }
@@ -120,9 +120,9 @@ void free_uid(struct user_struct *up)
         }
 }
 
-struct user_struct * alloc_uid(uid_t uid)
+struct user_struct * alloc_uid(struct user_namespace *ns, uid_t uid)
 {
-        struct list_head *hashent = uidhashentry(uid);
+        struct list_head *hashent = uidhashentry(ns, uid);
         struct user_struct *up;
 
         spin_lock_irq(&uidhash_lock);
@@ -211,11 +211,11 @@ static int __init uid_cache_init(void)
                         0, SLAB_HWCACHE_ALIGN|SLAB_PANIC, NULL, NULL);
 
         for(n = 0; n < UIDHASH_SZ; ++n)
-                INIT_LIST_HEAD(uidhash_table + n);
+                INIT_LIST_HEAD(init_user_ns.uidhash_table + n);
 
         /* Insert the root user immediately (init already runs as root) */
         spin_lock_irq(&uidhash_lock);
-        uid_hash_insert(&root_user, uidhashentry(0));
+        uid_hash_insert(&root_user, uidhashentry(&init_user_ns, 0));
         spin_unlock_irq(&uidhash_lock);
 
         return 0;