Re: [PATCH 17/43] userns: Rework the user_namespace adding uid/gid mapping support

["Serge E. Hallyn" <serge-A9i7LUbDfNHQT0dZR+AlfA@public.gmane.org>]

Quoting Eric W. Beiderman (ebiederm-aS9lmoZGLiVWk0Htik3J/w@public.gmane.org):
> From: Eric W. Biederman <ebiederm-aS9lmoZGLiVWk0Htik3J/w@public.gmane.org>
> 
> - Convert the old uid mapping functions into compatibility wrappers
> - Add a uid/gid mapping layer from user space uid and gids to kernel
>   internal uids and gids that is extent based for simplicty and speed.
>   * Working with number space after mapping uids/gids into their kernel
>     internal version adds only mapping complexity over what we have today,
>     leaving the kernel code easy to understand and test.
> - Add proc files /proc/self/uid_map /proc/self/gid_map
>   These files display the mapping and allow a mapping to be added
>   if a mapping does not exist.
> - Allow entering the user namespace without a uid or gid mapping.
>   Since we are starting with an existing user our uids and gids
>   still have global mappings so are still valid and useful they just don't
>   have local mappings.  The requirement for things to work are global uid
>   and gid so it is odd but perfectly fine not to have a local uid
>   and gid mapping.
>   Not requiring global uid and gid mappings greatly simplifies
>   the logic of setting up the uid and gid mappings by allowing
>   the mappings to be set after the namespace is created which makes the
>   slight weirdness worth it.
> - Make the mappings in the initial user namespace to the global
>   uid/gid space explicit.  Today it is an identity mapping
>   but in the future we may want to twist this for debugging, similar
>   to what we do with jiffies.
> - Document the memory ordering requirements of setting the uid and
>   gid mappings.  We only allow the mappings to be set once
>   and there are no pointers involved so the requirments are
>   trivial but a little atypical.
> 
> Performance:
> 
> In this scheme for the permission checks the performance is expected to
> stay the same as the actuall machine instructions should remain the same.
> 
> The worst case I could think of is ls -l on a large directory where
> all of the stat results need to be translated with from kuids and
> kgids to uids and gids.  So I benchmarked that case on my laptop
> with a dual core hyperthread Intel i5-2520M cpu with 3M of cpu cache.
> 
> My benchmark consisted of going to single user mode where nothing else
> was running. On an ext4 filesystem opening 1,000,000 files and looping
> through all of the files 1000 times and calling fstat on the
> individuals files.  This was to ensure I was benchmarking stat times
> where the inodes were in the kernels cache, but the inode values were
> not in the processors cache.  My results:
> 
> v3.4-rc1:         ~= 156ns (unmodified v3.4-rc1 with user namespace support disabled)
> v3.4-rc1-userns-: ~= 155ns (v3.4-rc1 with my user namespace patches and user namespace support disabled)
> v3.4-rc1-userns+: ~= 164ns (v3.4-rc1 with my user namespace patches and user namespace support enabled)
> 
> All of the configurations ran in roughly 120ns when I performed tests
> that ran in the cpu cache.
> 
> So in summary the performance impact is:
> 1ns improvement in the worst case with user namespace support compiled out.
> 8ns aka 5% slowdown in the worst case with user namespace support compiled in.
> 
> Signed-off-by: Eric W. Biederman <ebiederm-aS9lmoZGLiVWk0Htik3J/w@public.gmane.org>

Acked-by: Serge Hallyn <serge.hallyn-Z7WLFzj8eWMS+FvcfC7Uqw@public.gmane.org>

> ---
>  fs/proc/base.c                 |   77 ++++++
>  include/linux/uidgid.h         |   24 ++
>  include/linux/user_namespace.h |   30 ++-
>  kernel/user.c                  |   16 ++
>  kernel/user_namespace.c        |  545 +++++++++++++++++++++++++++++++++++++---
>  5 files changed, 644 insertions(+), 48 deletions(-)
> 
> diff --git a/fs/proc/base.c b/fs/proc/base.c
> index 1c8b280..2ee514c 100644
> --- a/fs/proc/base.c
> +++ b/fs/proc/base.c
> @@ -81,6 +81,7 @@
>  #include <linux/oom.h>
>  #include <linux/elf.h>
>  #include <linux/pid_namespace.h>
> +#include <linux/user_namespace.h>
>  #include <linux/fs_struct.h>
>  #include <linux/slab.h>
>  #include <linux/flex_array.h>
> @@ -2943,6 +2944,74 @@ static int proc_tgid_io_accounting(struct task_struct *task, char *buffer)
>  }
>  #endif /* CONFIG_TASK_IO_ACCOUNTING */
>  
> +#ifdef CONFIG_USER_NS
> +static int proc_id_map_open(struct inode *inode, struct file *file,
> +	struct seq_operations *seq_ops)
> +{
> +	struct user_namespace *ns = NULL;
> +	struct task_struct *task;
> +	struct seq_file *seq;
> +	int ret = -EINVAL;
> +
> +	task = get_proc_task(inode);
> +	if (task) {
> +		rcu_read_lock();
> +		ns = get_user_ns(task_cred_xxx(task, user_ns));
> +		rcu_read_unlock();
> +		put_task_struct(task);
> +	}
> +	if (!ns)
> +		goto err;
> +
> +	ret = seq_open(file, seq_ops);
> +	if (ret)
> +		goto err_put_ns;
> +
> +	seq = file->private_data;
> +	seq->private = ns;
> +
> +	return 0;
> +err_put_ns:
> +	put_user_ns(ns);
> +err:
> +	return ret;
> +}
> +
> +static int proc_id_map_release(struct inode *inode, struct file *file)
> +{
> +	struct seq_file *seq = file->private_data;
> +	struct user_namespace *ns = seq->private;
> +	put_user_ns(ns);
> +	return seq_release(inode, file);
> +}
> +
> +static int proc_uid_map_open(struct inode *inode, struct file *file)
> +{
> +	return proc_id_map_open(inode, file, &proc_uid_seq_operations);
> +}
> +
> +static int proc_gid_map_open(struct inode *inode, struct file *file)
> +{
> +	return proc_id_map_open(inode, file, &proc_gid_seq_operations);
> +}
> +
> +static const struct file_operations proc_uid_map_operations = {
> +	.open		= proc_uid_map_open,
> +	.write		= proc_uid_map_write,
> +	.read		= seq_read,
> +	.llseek		= seq_lseek,
> +	.release	= proc_id_map_release,
> +};
> +
> +static const struct file_operations proc_gid_map_operations = {
> +	.open		= proc_gid_map_open,
> +	.write		= proc_gid_map_write,
> +	.read		= seq_read,
> +	.llseek		= seq_lseek,
> +	.release	= proc_id_map_release,
> +};
> +#endif /* CONFIG_USER_NS */
> +
>  static int proc_pid_personality(struct seq_file *m, struct pid_namespace *ns,
>  				struct pid *pid, struct task_struct *task)
>  {
> @@ -3045,6 +3114,10 @@ static const struct pid_entry tgid_base_stuff[] = {
>  #ifdef CONFIG_HARDWALL
>  	INF("hardwall",   S_IRUGO, proc_pid_hardwall),
>  #endif
> +#ifdef CONFIG_USER_NS
> +	REG("uid_map",    S_IRUGO|S_IWUSR, proc_uid_map_operations),
> +	REG("gid_map",    S_IRUGO|S_IWUSR, proc_gid_map_operations),
> +#endif
>  };
>  
>  static int proc_tgid_base_readdir(struct file * filp,
> @@ -3400,6 +3473,10 @@ static const struct pid_entry tid_base_stuff[] = {
>  #ifdef CONFIG_HARDWALL
>  	INF("hardwall",   S_IRUGO, proc_pid_hardwall),
>  #endif
> +#ifdef CONFIG_USER_NS
> +	REG("uid_map",    S_IRUGO|S_IWUSR, proc_uid_map_operations),
> +	REG("gid_map",    S_IRUGO|S_IWUSR, proc_gid_map_operations),
> +#endif
>  };
>  
>  static int proc_tid_base_readdir(struct file * filp,
> diff --git a/include/linux/uidgid.h b/include/linux/uidgid.h
> index 5398568..8e522cbc 100644
> --- a/include/linux/uidgid.h
> +++ b/include/linux/uidgid.h
> @@ -127,6 +127,28 @@ static inline bool gid_valid(kgid_t gid)
>  	return !gid_eq(gid, INVALID_GID);
>  }
>  
> +#ifdef CONFIG_USER_NS
> +
> +extern kuid_t make_kuid(struct user_namespace *from, uid_t uid);
> +extern kgid_t make_kgid(struct user_namespace *from, gid_t gid);
> +
> +extern uid_t from_kuid(struct user_namespace *to, kuid_t uid);
> +extern gid_t from_kgid(struct user_namespace *to, kgid_t gid);
> +extern uid_t from_kuid_munged(struct user_namespace *to, kuid_t uid);
> +extern gid_t from_kgid_munged(struct user_namespace *to, kgid_t gid);
> +
> +static inline bool kuid_has_mapping(struct user_namespace *ns, kuid_t uid)
> +{
> +	return from_kuid(ns, uid) != (uid_t) -1;
> +}
> +
> +static inline bool kgid_has_mapping(struct user_namespace *ns, kgid_t gid)
> +{
> +	return from_kgid(ns, gid) != (gid_t) -1;
> +}
> +
> +#else
> +
>  static inline kuid_t make_kuid(struct user_namespace *from, uid_t uid)
>  {
>  	return KUIDT_INIT(uid);
> @@ -173,4 +195,6 @@ static inline bool kgid_has_mapping(struct user_namespace *ns, kgid_t gid)
>  	return true;
>  }
>  
> +#endif /* CONFIG_USER_NS */
> +
>  #endif /* _LINUX_UIDGID_H */
> diff --git a/include/linux/user_namespace.h b/include/linux/user_namespace.h
> index 8a391bd..4c9846d 100644
> --- a/include/linux/user_namespace.h
> +++ b/include/linux/user_namespace.h
> @@ -6,7 +6,20 @@
>  #include <linux/sched.h>
>  #include <linux/err.h>
>  
> +#define UID_GID_MAP_MAX_EXTENTS 5
> +
> +struct uid_gid_map {	/* 64 bytes -- 1 cache line */
> +	u32 nr_extents;
> +	struct uid_gid_extent {
> +		u32 first;
> +		u32 lower_first;
> +		u32 count;
> +	} extent[UID_GID_MAP_MAX_EXTENTS];
> +};
> +
>  struct user_namespace {
> +	struct uid_gid_map	uid_map;
> +	struct uid_gid_map	gid_map;
>  	struct kref		kref;
>  	struct user_namespace	*parent;
>  	kuid_t			owner;
> @@ -33,9 +46,11 @@ static inline void put_user_ns(struct user_namespace *ns)
>  		kref_put(&ns->kref, free_user_ns);
>  }
>  
> -uid_t user_ns_map_uid(struct user_namespace *to, const struct cred *cred, uid_t uid);
> -gid_t user_ns_map_gid(struct user_namespace *to, const struct cred *cred, gid_t gid);
> -
> +struct seq_operations;
> +extern struct seq_operations proc_uid_seq_operations;
> +extern struct seq_operations proc_gid_seq_operations;
> +extern ssize_t proc_uid_map_write(struct file *, const char __user *, size_t, loff_t *);
> +extern ssize_t proc_gid_map_write(struct file *, const char __user *, size_t, loff_t *);
>  #else
>  
>  static inline struct user_namespace *get_user_ns(struct user_namespace *ns)
> @@ -52,17 +67,18 @@ static inline void put_user_ns(struct user_namespace *ns)
>  {
>  }
>  
> +#endif
> +
>  static inline uid_t user_ns_map_uid(struct user_namespace *to,
>  	const struct cred *cred, uid_t uid)
>  {
> -	return uid;
> +	return from_kuid_munged(to, make_kuid(cred->user_ns, uid));
>  }
> +
>  static inline gid_t user_ns_map_gid(struct user_namespace *to,
>  	const struct cred *cred, gid_t gid)
>  {
> -	return gid;
> +	return from_kgid_munged(to, make_kgid(cred->user_ns, gid));
>  }
>  
> -#endif
> -
>  #endif /* _LINUX_USER_H */
> diff --git a/kernel/user.c b/kernel/user.c
> index cff3856..f9e420e 100644
> --- a/kernel/user.c
> +++ b/kernel/user.c
> @@ -22,6 +22,22 @@
>   * and 1 for... ?
>   */
>  struct user_namespace init_user_ns = {
> +	.uid_map = {
> +		.nr_extents = 1,
> +		.extent[0] = {
> +			.first = 0,
> +			.lower_first = 0,
> +			.count = 4294967295,
> +		},
> +	},
> +	.gid_map = {
> +		.nr_extents = 1,
> +		.extent[0] = {
> +			.first = 0,
> +			.lower_first = 0,
> +			.count = 4294967295,
> +		},
> +	},
>  	.kref = {
>  		.refcount	= ATOMIC_INIT(3),
>  	},
> diff --git a/kernel/user_namespace.c b/kernel/user_namespace.c
> index f69741a..9991bac 100644
> --- a/kernel/user_namespace.c
> +++ b/kernel/user_namespace.c
> @@ -12,9 +12,19 @@
>  #include <linux/highuid.h>
>  #include <linux/cred.h>
>  #include <linux/securebits.h>
> +#include <linux/keyctl.h>
> +#include <linux/key-type.h>
> +#include <keys/user-type.h>
> +#include <linux/seq_file.h>
> +#include <linux/fs.h>
> +#include <linux/uaccess.h>
> +#include <linux/ctype.h>
>  
>  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);
> +
>  /*
>   * 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
> @@ -26,7 +36,6 @@ static struct kmem_cache *user_ns_cachep __read_mostly;
>  int create_user_ns(struct cred *new)
>  {
>  	struct user_namespace *ns, *parent_ns = new->user_ns;
> -	struct user_struct *root_user;
>  	kuid_t owner = make_kuid(new->user_ns, new->euid);
>  	kgid_t group = make_kgid(new->user_ns, new->egid);
>  
> @@ -38,29 +47,15 @@ int create_user_ns(struct cred *new)
>  	    !kgid_has_mapping(parent_ns, group))
>  		return -EPERM;
>  
> -	ns = kmem_cache_alloc(user_ns_cachep, GFP_KERNEL);
> +	ns = kmem_cache_zalloc(user_ns_cachep, GFP_KERNEL);
>  	if (!ns)
>  		return -ENOMEM;
>  
>  	kref_init(&ns->kref);
> -
> -	/* Alloc new root user.  */
> -	root_user = alloc_uid(make_kuid(ns, 0));
> -	if (!root_user) {
> -		kmem_cache_free(user_ns_cachep, ns);
> -		return -ENOMEM;
> -	}
> -
> -	/* set the new root user in the credentials under preparation */
>  	ns->parent = parent_ns;
>  	ns->owner = owner;
>  	ns->group = group;
> -	free_uid(new->user);
> -	new->user = root_user;
> -	new->uid = new->euid = new->suid = new->fsuid = 0;
> -	new->gid = new->egid = new->sgid = new->fsgid = 0;
> -	put_group_info(new->group_info);
> -	new->group_info = get_group_info(&init_groups);
> +
>  	/* Start with the same capabilities as init but useless for doing
>  	 * anything as the capabilities are bound to the new user namespace.
>  	 */
> @@ -92,44 +87,512 @@ void free_user_ns(struct kref *kref)
>  }
>  EXPORT_SYMBOL(free_user_ns);
>  
> -uid_t user_ns_map_uid(struct user_namespace *to, const struct cred *cred, uid_t uid)
> +static u32 map_id_range_down(struct uid_gid_map *map, u32 id, u32 count)
>  {
> -	struct user_namespace *tmp;
> +	unsigned idx, extents;
> +	u32 first, last, id2;
>  
> -	if (likely(to == cred->user_ns))
> -		return uid;
> +	id2 = id + count - 1;
>  
> -	/* Is cred->user the creator of the target user_ns
> -	 * or the creator of one of it's parents?
> -	 */
> -	for ( tmp = to; tmp != &init_user_ns; tmp = tmp->parent ) {
> -		if (uid_eq(cred->user->uid, tmp->owner)) {
> -			return (uid_t)0;
> -		}
> +	/* Find the matching extent */
> +	extents = map->nr_extents;
> +	smp_read_barrier_depends();
> +	for (idx = 0; idx < extents; idx++) {
> +		first = map->extent[idx].first;
> +		last = first + map->extent[idx].count - 1;
> +		if (id >= first && id <= last &&
> +		    (id2 >= first && id2 <= last))
> +			break;
> +	}
> +	/* Map the id or note failure */
> +	if (idx < extents)
> +		id = (id - first) + map->extent[idx].lower_first;
> +	else
> +		id = (u32) -1;
> +
> +	return id;
> +}
> +
> +static u32 map_id_down(struct uid_gid_map *map, u32 id)
> +{
> +	unsigned idx, extents;
> +	u32 first, last;
> +
> +	/* Find the matching extent */
> +	extents = map->nr_extents;
> +	smp_read_barrier_depends();
> +	for (idx = 0; idx < extents; idx++) {
> +		first = map->extent[idx].first;
> +		last = first + map->extent[idx].count - 1;
> +		if (id >= first && id <= last)
> +			break;
> +	}
> +	/* Map the id or note failure */
> +	if (idx < extents)
> +		id = (id - first) + map->extent[idx].lower_first;
> +	else
> +		id = (u32) -1;
> +
> +	return id;
> +}
> +
> +static u32 map_id_up(struct uid_gid_map *map, u32 id)
> +{
> +	unsigned idx, extents;
> +	u32 first, last;
> +
> +	/* Find the matching extent */
> +	extents = map->nr_extents;
> +	smp_read_barrier_depends();
> +	for (idx = 0; idx < extents; idx++) {
> +		first = map->extent[idx].lower_first;
> +		last = first + map->extent[idx].count - 1;
> +		if (id >= first && id <= last)
> +			break;
>  	}
> +	/* Map the id or note failure */
> +	if (idx < extents)
> +		id = (id - first) + map->extent[idx].first;
> +	else
> +		id = (u32) -1;
> +
> +	return id;
> +}
> +
> +/**
> + *	make_kuid - Map a user-namespace uid pair into a kuid.
> + *	@ns:  User namespace that the uid is in
> + *	@uid: User identifier
> + *
> + *	Maps a user-namespace uid pair into a kernel internal kuid,
> + *	and returns that kuid.
> + *
> + *	When there is no mapping defined for the user-namespace uid
> + *	pair INVALID_UID is returned.  Callers are expected to test
> + *	for and handle handle INVALID_UID being returned.  INVALID_UID
> + *	may be tested for using uid_valid().
> + */
> +kuid_t make_kuid(struct user_namespace *ns, uid_t uid)
> +{
> +	/* Map the uid to a global kernel uid */
> +	return KUIDT_INIT(map_id_down(&ns->uid_map, uid));
> +}
> +EXPORT_SYMBOL(make_kuid);
> +
> +/**
> + *	from_kuid - Create a uid from a kuid user-namespace pair.
> + *	@targ: The user namespace we want a uid in.
> + *	@kuid: The kernel internal uid to start with.
> + *
> + *	Map @kuid into the user-namespace specified by @targ and
> + *	return the resulting uid.
> + *
> + *	There is always a mapping into the initial user_namespace.
> + *
> + *	If @kuid has no mapping in @targ (uid_t)-1 is returned.
> + */
> +uid_t from_kuid(struct user_namespace *targ, kuid_t kuid)
> +{
> +	/* Map the uid from a global kernel uid */
> +	return map_id_up(&targ->uid_map, __kuid_val(kuid));
> +}
> +EXPORT_SYMBOL(from_kuid);
> +
> +/**
> + *	from_kuid_munged - Create a uid from a kuid user-namespace pair.
> + *	@targ: The user namespace we want a uid in.
> + *	@kuid: The kernel internal uid to start with.
> + *
> + *	Map @kuid into the user-namespace specified by @targ and
> + *	return the resulting uid.
> + *
> + *	There is always a mapping into the initial user_namespace.
> + *
> + *	Unlike from_kuid from_kuid_munged never fails and always
> + *	returns a valid uid.  This makes from_kuid_munged appropriate
> + *	for use in syscalls like stat and getuid where failing the
> + *	system call and failing to provide a valid uid are not an
> + *	options.
> + *
> + *	If @kuid has no mapping in @targ overflowuid is returned.
> + */
> +uid_t from_kuid_munged(struct user_namespace *targ, kuid_t kuid)
> +{
> +	uid_t uid;
> +	uid = from_kuid(targ, kuid);
> +
> +	if (uid == (uid_t) -1)
> +		uid = overflowuid;
> +	return uid;
> +}
> +EXPORT_SYMBOL(from_kuid_munged);
> +
> +/**
> + *	make_kgid - Map a user-namespace gid pair into a kgid.
> + *	@ns:  User namespace that the gid is in
> + *	@uid: group identifier
> + *
> + *	Maps a user-namespace gid pair into a kernel internal kgid,
> + *	and returns that kgid.
> + *
> + *	When there is no mapping defined for the user-namespace gid
> + *	pair INVALID_GID is returned.  Callers are expected to test
> + *	for and handle INVALID_GID being returned.  INVALID_GID may be
> + *	tested for using gid_valid().
> + */
> +kgid_t make_kgid(struct user_namespace *ns, gid_t gid)
> +{
> +	/* Map the gid to a global kernel gid */
> +	return KGIDT_INIT(map_id_down(&ns->gid_map, gid));
> +}
> +EXPORT_SYMBOL(make_kgid);
> +
> +/**
> + *	from_kgid - Create a gid from a kgid user-namespace pair.
> + *	@targ: The user namespace we want a gid in.
> + *	@kgid: The kernel internal gid to start with.
> + *
> + *	Map @kgid into the user-namespace specified by @targ and
> + *	return the resulting gid.
> + *
> + *	There is always a mapping into the initial user_namespace.
> + *
> + *	If @kgid has no mapping in @targ (gid_t)-1 is returned.
> + */
> +gid_t from_kgid(struct user_namespace *targ, kgid_t kgid)
> +{
> +	/* Map the gid from a global kernel gid */
> +	return map_id_up(&targ->gid_map, __kgid_val(kgid));
> +}
> +EXPORT_SYMBOL(from_kgid);
> +
> +/**
> + *	from_kgid_munged - Create a gid from a kgid user-namespace pair.
> + *	@targ: The user namespace we want a gid in.
> + *	@kgid: The kernel internal gid to start with.
> + *
> + *	Map @kgid into the user-namespace specified by @targ and
> + *	return the resulting gid.
> + *
> + *	There is always a mapping into the initial user_namespace.
> + *
> + *	Unlike from_kgid from_kgid_munged never fails and always
> + *	returns a valid gid.  This makes from_kgid_munged appropriate
> + *	for use in syscalls like stat and getgid where failing the
> + *	system call and failing to provide a valid gid are not options.
> + *
> + *	If @kgid has no mapping in @targ overflowgid is returned.
> + */
> +gid_t from_kgid_munged(struct user_namespace *targ, kgid_t kgid)
> +{
> +	gid_t gid;
> +	gid = from_kgid(targ, kgid);
> +
> +	if (gid == (gid_t) -1)
> +		gid = overflowgid;
> +	return gid;
> +}
> +EXPORT_SYMBOL(from_kgid_munged);
> +
> +static int uid_m_show(struct seq_file *seq, void *v)
> +{
> +	struct user_namespace *ns = seq->private;
> +	struct uid_gid_extent *extent = v;
> +	struct user_namespace *lower_ns;
> +	uid_t lower;
>  
> -	/* No useful relationship so no mapping */
> -	return overflowuid;
> +	lower_ns = current_user_ns();
> +	if ((lower_ns == ns) && lower_ns->parent)
> +		lower_ns = lower_ns->parent;
> +
> +	lower = from_kuid(lower_ns, KUIDT_INIT(extent->lower_first));
> +
> +	seq_printf(seq, "%10u %10u %10u\n",
> +		extent->first,
> +		lower,
> +		extent->count);
> +
> +	return 0;
>  }
>  
> -gid_t user_ns_map_gid(struct user_namespace *to, const struct cred *cred, gid_t gid)
> +static int gid_m_show(struct seq_file *seq, void *v)
>  {
> -	struct user_namespace *tmp;
> +	struct user_namespace *ns = seq->private;
> +	struct uid_gid_extent *extent = v;
> +	struct user_namespace *lower_ns;
> +	gid_t lower;
>  
> -	if (likely(to == cred->user_ns))
> -		return gid;
> +	lower_ns = current_user_ns();
> +	if ((lower_ns == ns) && lower_ns->parent)
> +		lower_ns = lower_ns->parent;
>  
> -	/* Is cred->user the creator of the target user_ns
> -	 * or the creator of one of it's parents?
> +	lower = from_kgid(lower_ns, KGIDT_INIT(extent->lower_first));
> +
> +	seq_printf(seq, "%10u %10u %10u\n",
> +		extent->first,
> +		lower,
> +		extent->count);
> +
> +	return 0;
> +}
> +
> +static void *m_start(struct seq_file *seq, loff_t *ppos, struct uid_gid_map *map)
> +{
> +	struct uid_gid_extent *extent = NULL;
> +	loff_t pos = *ppos;
> +
> +	if (pos < map->nr_extents)
> +		extent = &map->extent[pos];
> +
> +	return extent;
> +}
> +
> +static void *uid_m_start(struct seq_file *seq, loff_t *ppos)
> +{
> +	struct user_namespace *ns = seq->private;
> +
> +	return m_start(seq, ppos, &ns->uid_map);
> +}
> +
> +static void *gid_m_start(struct seq_file *seq, loff_t *ppos)
> +{
> +	struct user_namespace *ns = seq->private;
> +
> +	return m_start(seq, ppos, &ns->gid_map);
> +}
> +
> +static void *m_next(struct seq_file *seq, void *v, loff_t *pos)
> +{
> +	(*pos)++;
> +	return seq->op->start(seq, pos);
> +}
> +
> +static void m_stop(struct seq_file *seq, void *v)
> +{
> +	return;
> +}
> +
> +struct seq_operations proc_uid_seq_operations = {
> +	.start = uid_m_start,
> +	.stop = m_stop,
> +	.next = m_next,
> +	.show = uid_m_show,
> +};
> +
> +struct seq_operations proc_gid_seq_operations = {
> +	.start = gid_m_start,
> +	.stop = m_stop,
> +	.next = m_next,
> +	.show = gid_m_show,
> +};
> +
> +static DEFINE_MUTEX(id_map_mutex);
> +
> +static ssize_t map_write(struct file *file, const char __user *buf,
> +			 size_t count, loff_t *ppos,
> +			 int cap_setid,
> +			 struct uid_gid_map *map,
> +			 struct uid_gid_map *parent_map)
> +{
> +	struct seq_file *seq = file->private_data;
> +	struct user_namespace *ns = seq->private;
> +	struct uid_gid_map new_map;
> +	unsigned idx;
> +	struct uid_gid_extent *extent, *last = NULL;
> +	unsigned long page = 0;
> +	char *kbuf, *pos, *next_line;
> +	ssize_t ret = -EINVAL;
> +
> +	/*
> +	 * The id_map_mutex serializes all writes to any given map.
> +	 *
> +	 * Any map is only ever written once.
> +	 *
> +	 * An id map fits within 1 cache line on most architectures.
> +	 *
> +	 * On read nothing needs to be done unless you are on an
> +	 * architecture with a crazy cache coherency model like alpha.
> +	 *
> +	 * There is a one time data dependency between reading the
> +	 * count of the extents and the values of the extents.  The
> +	 * desired behavior is to see the values of the extents that
> +	 * were written before the count of the extents.
> +	 *
> +	 * To achieve this smp_wmb() is used on guarantee the write
> +	 * order and smp_read_barrier_depends() is guaranteed that we
> +	 * don't have crazy architectures returning stale data.
> +	 *
> +	 */
> +	mutex_lock(&id_map_mutex);
> +
> +	ret = -EPERM;
> +	/* Only allow one successful write to the map */
> +	if (map->nr_extents != 0)
> +		goto out;
> +
> +	/* Require the appropriate privilege CAP_SETUID or CAP_SETGID
> +	 * over the user namespace in order to set the id mapping.
>  	 */
> -	for ( tmp = to; tmp != &init_user_ns; tmp = tmp->parent ) {
> -		if (uid_eq(cred->user->uid, tmp->owner)) {
> -			return (gid_t)0;
> +	if (!ns_capable(ns, cap_setid))
> +		goto out;
> +
> +	/* Get a buffer */
> +	ret = -ENOMEM;
> +	page = __get_free_page(GFP_TEMPORARY);
> +	kbuf = (char *) page;
> +	if (!page)
> +		goto out;
> +
> +	/* Only allow <= page size writes at the beginning of the file */
> +	ret = -EINVAL;
> +	if ((*ppos != 0) || (count >= PAGE_SIZE))
> +		goto out;
> +
> +	/* Slurp in the user data */
> +	ret = -EFAULT;
> +	if (copy_from_user(kbuf, buf, count))
> +		goto out;
> +	kbuf[count] = '\0';
> +
> +	/* Parse the user data */
> +	ret = -EINVAL;
> +	pos = kbuf;
> +	new_map.nr_extents = 0;
> +	for (;pos; pos = next_line) {
> +		extent = &new_map.extent[new_map.nr_extents];
> +
> +		/* Find the end of line and ensure I don't look past it */
> +		next_line = strchr(pos, '\n');
> +		if (next_line) {
> +			*next_line = '\0';
> +			next_line++;
> +			if (*next_line == '\0')
> +				next_line = NULL;
>  		}
> +
> +		pos = skip_spaces(pos);
> +		extent->first = simple_strtoul(pos, &pos, 10);
> +		if (!isspace(*pos))
> +			goto out;
> +
> +		pos = skip_spaces(pos);
> +		extent->lower_first = simple_strtoul(pos, &pos, 10);
> +		if (!isspace(*pos))
> +			goto out;
> +
> +		pos = skip_spaces(pos);
> +		extent->count = simple_strtoul(pos, &pos, 10);
> +		if (*pos && !isspace(*pos))
> +			goto out;
> +
> +		/* Verify there is not trailing junk on the line */
> +		pos = skip_spaces(pos);
> +		if (*pos != '\0')
> +			goto out;
> +
> +		/* Verify we have been given valid starting values */
> +		if ((extent->first == (u32) -1) ||
> +		    (extent->lower_first == (u32) -1 ))
> +			goto out;
> +
> +		/* Verify count is not zero and does not cause the extent to wrap */
> +		if ((extent->first + extent->count) <= extent->first)
> +			goto out;
> +		if ((extent->lower_first + extent->count) <= extent->lower_first)
> +			goto out;
> +
> +		/* For now only accept extents that are strictly in order */
> +		if (last &&
> +		    (((last->first + last->count) > extent->first) ||
> +		     ((last->lower_first + last->count) > extent->lower_first)))
> +			goto out;
> +
> +		new_map.nr_extents++;
> +		last = extent;
> +
> +		/* Fail if the file contains too many extents */
> +		if ((new_map.nr_extents == UID_GID_MAP_MAX_EXTENTS) &&
> +		    (next_line != NULL))
> +			goto out;
>  	}
> +	/* Be very certaint the new map actually exists */
> +	if (new_map.nr_extents == 0)
> +		goto out;
> +
> +	ret = -EPERM;
> +	/* Validate the user is allowed to use user id's mapped to. */
> +	if (!new_idmap_permitted(ns, cap_setid, &new_map))
> +		goto out;
> +
> +	/* Map the lower ids from the parent user namespace to the
> +	 * kernel global id space.
> +	 */
> +	for (idx = 0; idx < new_map.nr_extents; idx++) {
> +		u32 lower_first;
> +		extent = &new_map.extent[idx];
> +
> +		lower_first = map_id_range_down(parent_map,
> +						extent->lower_first,
> +						extent->count);
> +
> +		/* Fail if we can not map the specified extent to
> +		 * the kernel global id space.
> +		 */
> +		if (lower_first == (u32) -1)
> +			goto out;
> +
> +		extent->lower_first = lower_first;
> +	}
> +
> +	/* Install the map */
> +	memcpy(map->extent, new_map.extent,
> +		new_map.nr_extents*sizeof(new_map.extent[0]));
> +	smp_wmb();
> +	map->nr_extents = new_map.nr_extents;
> +
> +	*ppos = count;
> +	ret = count;
> +out:
> +	mutex_unlock(&id_map_mutex);
> +	if (page)
> +		free_page(page);
> +	return ret;
> +}
> +
> +ssize_t proc_uid_map_write(struct file *file, const char __user *buf, size_t size, loff_t *ppos)
> +{
> +	struct seq_file *seq = file->private_data;
> +	struct user_namespace *ns = seq->private;
> +
> +	if (!ns->parent)
> +		return -EPERM;
> +
> +	return map_write(file, buf, size, ppos, CAP_SETUID,
> +			 &ns->uid_map, &ns->parent->uid_map);
> +}
> +
> +ssize_t proc_gid_map_write(struct file *file, const char __user *buf, size_t size, loff_t *ppos)
> +{
> +	struct seq_file *seq = file->private_data;
> +	struct user_namespace *ns = seq->private;
> +
> +	if (!ns->parent)
> +		return -EPERM;
> +
> +	return map_write(file, buf, size, ppos, CAP_SETGID,
> +			 &ns->gid_map, &ns->parent->gid_map);
> +}
> +
> +static bool new_idmap_permitted(struct user_namespace *ns, int cap_setid,
> +				struct uid_gid_map *new_map)
> +{
> +	/* Allow the specified ids if we have the appropriate capability
> +	 * (CAP_SETUID or CAP_SETGID) over the parent user namespace.
> +	 */
> +	if (ns_capable(ns->parent, cap_setid))
> +		return true;
>  
> -	/* No useful relationship so no mapping */
> -	return overflowgid;
> +	return false;
>  }
>  
>  static __init int user_namespaces_init(void)
> -- 
> 1.7.2.5
> 
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