user namespace : add unshare

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 <[email protected]>

Signed-off-by Serge E. Hallyn <[email protected]>

Signed-off-by Andrew Morton <[email protected]>

Acked-by Pavel Emelianov <[email protected]>

Cc Herbert Poetzl <[email protected]>

Cc Kirill Korotaev <[email protected]>

Cc Eric W. Biederman <[email protected]>

---

 include/linux/init_task.h      |    2 +
 include/linux/nsproxy.h        |    1 
 include/linux/sched.h          |    3 +-
 include/linux/user_namespace.h |   57 +++++++++++++++++++++++++++++++++++++++++
 init/Kconfig                   |    9 ++++++
 kernel/Makefile                |    2 -
 kernel/fork.c                  |    2 -
 kernel/nsproxy.c               |    9 ++++++
 kernel/sys.c                   |    5 ++-
 kernel/user.c                  |   18 ++++++------
 kernel/user_namespace.c        |   43 ++++++++++++++++++++++++++++++
 11 files changed, 137 insertions(+), 14 deletions(-)

Index: 2.6.22-rc4-mm2/include/linux/init_task.h
===================================================================

include/linux/init_task.h +2 -0

@@ -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) {						\

Index: 2.6.22-rc4-mm2/include/linux/nsproxy.h
===================================================================

include/linux/nsproxy.h +1 -0

@@ -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;
 

Index: 2.6.22-rc4-mm2/include/linux/sched.h
===================================================================

include/linux/sched.h +2 -1

@@ -268,6 +268,7 @@ extern signed long schedule_timeout_unin
 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

@@ -1378,7 +1379,7 @@ extern struct task_struct *find_task_by_
 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);

Index: 2.6.22-rc4-mm2/include/linux/user_namespace.h
===================================================================

include/linux/user_namespace.h new file +57 -0

@@ -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 */

Index: 2.6.22-rc4-mm2/init/Kconfig
===================================================================

init/Kconfig +9 -0

@@ -231,6 +231,15 @@ 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

Index: 2.6.22-rc4-mm2/kernel/Makefile
===================================================================

kernel/Makefile +1 -1

@@ -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 \

Index: 2.6.22-rc4-mm2/kernel/fork.c
===================================================================

kernel/fork.c +1 -1

@@ -1004,7 +1004,7 @@ static struct task_struct *copy_process(
 	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;
 	}
 

Index: 2.6.22-rc4-mm2/kernel/nsproxy.c
===================================================================

kernel/nsproxy.c +9 -0

@@ -79,8 +79,15 @@ static struct nsproxy *create_new_namesp
 	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);
 }
 

Index: 2.6.22-rc4-mm2/kernel/sys.c
===================================================================

kernel/sys.c +3 -2

@@ -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 
 {
 	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;
 	}

Index: 2.6.22-rc4-mm2/kernel/user.c
===================================================================

kernel/user.c +9 -9

@@ -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;

Index: 2.6.22-rc4-mm2/kernel/user_namespace.c
===================================================================

kernel/user_namespace.c new file +43 -1

@@ -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 */
-

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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 ?)

Quoted 3 lines · On Fri, 08 Jun 2007 17:14:07 +0200 Cedric Le Goater <[email protected]> wrote:

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.

Quoted 3 lines

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 ?)

This second paragraph is distressingly indecisive. How much thought has gone into this??

For a start, it seems wrong for the kernel to hardwire knowledge about UID 0 in this fashion.

I'd have thought that a better model for user-namespace unsharing would be to do a copy-by-value of the entire namespace, then permit a suitably-privileged application to go through and kill off any unwanted users from the now-unshared user namespace.

Or maybe just remove that "Insert new root user" altogether? What would then go wrong?