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>

11 files changed, 137 insertions, 14 deletions

diff --git a/include/linux/init_task.h b/include/linux/init_task.h
index 276ccaa2670c..cab741c2d603 100644
--- a/include/linux/init_task.h
+++ b/include/linux/init_task.h
@@ -8,6 +8,7 @@
 #include <linux/lockdep.h>
 #include <linux/ipc.h>
 #include <linux/pid_namespace.h>
+#include <linux/user_namespace.h>
 
 #define INIT_FDTABLE \
 {                                                       \
@@ -78,6 +79,7 @@ extern struct nsproxy init_nsproxy;
         .uts_ns         = &init_uts_ns,                                 \
         .mnt_ns         = NULL,                                         \
         INIT_IPC_NS(ipc_ns)                                             \
+        .user_ns        = &init_user_ns,                                \
 }
 
 #define INIT_SIGHAND(sighand) {                                         \
diff --git a/include/linux/nsproxy.h b/include/linux/nsproxy.h
index 189e0dc993ab..6d179a397bfb 100644
--- a/include/linux/nsproxy.h
+++ b/include/linux/nsproxy.h
@@ -28,6 +28,7 @@ struct nsproxy {
         struct ipc_namespace *ipc_ns;
         struct mnt_namespace *mnt_ns;
         struct pid_namespace *pid_ns;
+        struct user_namespace *user_ns;
 };
 extern struct nsproxy init_nsproxy;
 
diff --git a/include/linux/sched.h b/include/linux/sched.h
index b579624477f4..c667255d70db 100644
--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -287,6 +287,7 @@ extern signed long schedule_timeout_uninterruptible(signed long timeout);
 asmlinkage void schedule(void);
 
 struct nsproxy;
+struct user_namespace;
 
 /* Maximum number of active map areas.. This is a random (large) number */
 #define DEFAULT_MAX_MAP_COUNT   65536
@@ -1408,7 +1409,7 @@ extern struct task_struct *find_task_by_pid_type(int type, int pid);
 extern void __set_special_pids(pid_t session, pid_t pgrp);
 
 /* per-UID process charging. */
-extern struct user_struct * alloc_uid(uid_t);
+extern struct user_struct * alloc_uid(struct user_namespace *, uid_t);
 static inline struct user_struct *get_uid(struct user_struct *u)
 {
         atomic_inc(&u->__count);
diff --git a/include/linux/user_namespace.h b/include/linux/user_namespace.h
new file mode 100644
index 000000000000..92a45867ecfb
--- /dev/null
+++ b/include/linux/user_namespace.h
@@ -0,0 +1,57 @@
+#ifndef _LINUX_USER_NAMESPACE_H
+#define _LINUX_USER_NAMESPACE_H
+
+#include <linux/kref.h>
+#include <linux/nsproxy.h>
+#include <linux/sched.h>
+
+#define UIDHASH_BITS    (CONFIG_BASE_SMALL ? 3 : 8)
+#define UIDHASH_SZ      (1 << UIDHASH_BITS)
+
+struct user_namespace {
+        struct kref             kref;
+        struct list_head        uidhash_table[UIDHASH_SZ];
+        struct user_struct      *root_user;
+};
+
+extern struct user_namespace init_user_ns;
+
+#ifdef CONFIG_USER_NS
+
+static inline struct user_namespace *get_user_ns(struct user_namespace *ns)
+{
+        if (ns)
+                kref_get(&ns->kref);
+        return ns;
+}
+
+extern struct user_namespace *copy_user_ns(int flags,
+                                           struct user_namespace *old_ns);
+extern void free_user_ns(struct kref *kref);
+
+static inline void put_user_ns(struct user_namespace *ns)
+{
+        if (ns)
+                kref_put(&ns->kref, free_user_ns);
+}
+
+#else
+
+static inline struct user_namespace *get_user_ns(struct user_namespace *ns)
+{
+        return &init_user_ns;
+}
+
+static inline struct user_namespace *copy_user_ns(int flags,
+                                                  struct user_namespace *old_ns)
+{
+        return NULL;
+}
+
+static inline void put_user_ns(struct user_namespace *ns)
+{
+}
+
+#endif
+
+#endif /* _LINUX_USER_H */
diff --git a/init/Kconfig b/init/Kconfig
index 1e198b8c6936..0b0e29ed82d1 100644
--- a/init/Kconfig
+++ b/init/Kconfig
@@ -209,6 +209,15 @@ config TASK_IO_ACCOUNTING
 
           Say N if unsure.
 
+config USER_NS
+        bool "User Namespaces (EXPERIMENTAL)"
+        default n
+        depends on EXPERIMENTAL
+        help
+          Support user namespaces.  This allows containers, i.e.
+          vservers, to use user namespaces to provide different
+          user info for different servers.  If unsure, say N.
+
 config AUDIT
         bool "Auditing support"
         depends on NET
diff --git a/kernel/Makefile b/kernel/Makefile
index fa8efd437afb..2a999836ca18 100644
--- a/kernel/Makefile
+++ b/kernel/Makefile
@@ -4,7 +4,7 @@
 
 obj-y     = sched.o fork.o exec_domain.o panic.o printk.o profile.o \
             exit.o itimer.o time.o softirq.o resource.o \
-            sysctl.o capability.o ptrace.o timer.o user.o \
+            sysctl.o capability.o ptrace.o timer.o user.o user_namespace.o \
             signal.o sys.o kmod.o workqueue.o pid.o \
             rcupdate.o extable.o params.o posix-timers.o \
             kthread.o wait.o kfifo.o sys_ni.o posix-cpu-timers.o mutex.o \
diff --git a/kernel/fork.c b/kernel/fork.c
index 4015912aaac2..13cf0978780a 100644
--- a/kernel/fork.c
+++ b/kernel/fork.c
@@ -1002,7 +1002,7 @@ static struct task_struct *copy_process(unsigned long clone_flags,
         if (atomic_read(&p->user->processes) >=
                         p->signal->rlim[RLIMIT_NPROC].rlim_cur) {
                 if (!capable(CAP_SYS_ADMIN) && !capable(CAP_SYS_RESOURCE) &&
-                                p->user != &root_user)
+                    p->user != current->nsproxy->user_ns->root_user)
                         goto bad_fork_free;
         }
 
diff --git a/kernel/nsproxy.c b/kernel/nsproxy.c
index e38bed75367d..895e3a3f2044 100644
--- a/kernel/nsproxy.c
+++ b/kernel/nsproxy.c
@@ -79,8 +79,15 @@ static struct nsproxy *create_new_namespaces(int flags, struct task_struct *tsk,
         if (IS_ERR(new_nsp->pid_ns))
                 goto out_pid;
 
+        new_nsp->user_ns = copy_user_ns(flags, tsk->nsproxy->user_ns);
+        if (IS_ERR(new_nsp->user_ns))
+                goto out_user;
+
         return new_nsp;
 
+out_user:
+        if (new_nsp->pid_ns)
+                put_pid_ns(new_nsp->pid_ns);
 out_pid:
         if (new_nsp->ipc_ns)
                 put_ipc_ns(new_nsp->ipc_ns);
@@ -140,6 +147,8 @@ void free_nsproxy(struct nsproxy *ns)
                 put_ipc_ns(ns->ipc_ns);
         if (ns->pid_ns)
                 put_pid_ns(ns->pid_ns);
+        if (ns->user_ns)
+                put_user_ns(ns->user_ns);
         kfree(ns);
 }
 
diff --git a/kernel/sys.c b/kernel/sys.c
index 872271ccc384..ed92e2f03342 100644
--- a/kernel/sys.c
+++ b/kernel/sys.c
@@ -35,6 +35,7 @@
 #include <linux/compat.h>
 #include <linux/syscalls.h>
 #include <linux/kprobes.h>
+#include <linux/user_namespace.h>
 
 #include <asm/uaccess.h>
 #include <asm/io.h>
@@ -1078,13 +1079,13 @@ static int set_user(uid_t new_ruid, int dumpclear)
 {
         struct user_struct *new_user;
 
-        new_user = alloc_uid(new_ruid);
+        new_user = alloc_uid(current->nsproxy->user_ns, new_ruid);
         if (!new_user)
                 return -EAGAIN;
 
         if (atomic_read(&new_user->processes) >=
                                 current->signal->rlim[RLIMIT_NPROC].rlim_cur &&
-                        new_user != &root_user) {
+                        new_user != current->nsproxy->user_ns->root_user) {
                 free_uid(new_user);
                 return -EAGAIN;
         }
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;
diff --git a/kernel/user_namespace.c b/kernel/user_namespace.c
new file mode 100644
index 000000000000..3d7964209774
--- /dev/null
+++ b/kernel/user_namespace.c
@@ -0,0 +1,43 @@
+/*
+ *  This program is free software; you can redistribute it and/or
+ *  modify it under the terms of the GNU General Public License as
+ *  published by the Free Software Foundation, version 2 of the
+ *  License.
+ */
+
+#include <linux/module.h>
+#include <linux/version.h>
+#include <linux/nsproxy.h>
+#include <linux/user_namespace.h>
+
+struct user_namespace init_user_ns = {
+        .kref = {
+                .refcount       = ATOMIC_INIT(2),
+        },
+        .root_user = &root_user,
+};
+
+EXPORT_SYMBOL_GPL(init_user_ns);
+
+#ifdef CONFIG_USER_NS
+
+struct user_namespace * copy_user_ns(int flags, struct user_namespace *old_ns)
+{
+        struct user_namespace *new_ns;
+
+        BUG_ON(!old_ns);
+        get_user_ns(old_ns);
+
+        new_ns = old_ns;
+        return new_ns;
+}
+
+void free_user_ns(struct kref *kref)
+{
+        struct user_namespace *ns;
+
+        ns = container_of(kref, struct user_namespace, kref);
+        kfree(ns);
+}
+
+#endif /* CONFIG_USER_NS */