Re: [PATCH v3 01/25] user_namespace: introduce fsid mappings infrastructure

["Serge E. Hallyn" <serge@hallyn.com>]

On Tue, Feb 18, 2020 at 03:33:47PM +0100, Christian Brauner wrote:
> This introduces the infrastructure to setup fsid mappings which will be used in
> later patches.
> All new code depends on CONFIG_USER_NS_FSID=y. It currently defaults to "N".
> If CONFIG_USER_NS_FSID is not set, no new code is added.
> 
> In this patch fsuid_m_show() and fsgid_m_show() are introduced. They are
> identical to uid_m_show() and gid_m_show() until we introduce from_kfsuid() and
> from_kfsgid() in a follow-up patch.
> 
> Signed-off-by: Christian Brauner <christian.brauner@ubuntu.com>

Acked-by: Serge Hallyn <serge@hallyn.com>

> ---
> /* v2 */
> - Randy Dunlap <rdunlap@infradead.org>:
>   - Fix typo in USER_NS_FSID kconfig documentation.
> 
> /* v3 */
> unchanged
> ---
>  include/linux/user_namespace.h |  10 +++
>  init/Kconfig                   |  11 +++
>  kernel/user.c                  |  22 ++++++
>  kernel/user_namespace.c        | 122 +++++++++++++++++++++++++++++++++
>  4 files changed, 165 insertions(+)
> 
> diff --git a/include/linux/user_namespace.h b/include/linux/user_namespace.h
> index 6ef1c7109fc4..e44742b0cf8a 100644
> --- a/include/linux/user_namespace.h
> +++ b/include/linux/user_namespace.h
> @@ -56,6 +56,10 @@ enum ucount_type {
>  struct user_namespace {
>  	struct uid_gid_map	uid_map;
>  	struct uid_gid_map	gid_map;
> +#ifdef CONFIG_USER_NS_FSID
> +	struct uid_gid_map	fsuid_map;
> +	struct uid_gid_map	fsgid_map;
> +#endif
>  	struct uid_gid_map	projid_map;
>  	atomic_t		count;
>  	struct user_namespace	*parent;
> @@ -127,6 +131,12 @@ struct seq_operations;
>  extern const struct seq_operations proc_uid_seq_operations;
>  extern const struct seq_operations proc_gid_seq_operations;
>  extern const struct seq_operations proc_projid_seq_operations;
> +#ifdef CONFIG_USER_NS_FSID
> +extern const struct seq_operations proc_fsuid_seq_operations;
> +extern const struct seq_operations proc_fsgid_seq_operations;
> +extern ssize_t proc_fsuid_map_write(struct file *, const char __user *, size_t, loff_t *);
> +extern ssize_t proc_fsgid_map_write(struct file *, const char __user *, size_t, loff_t *);
> +#endif
>  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 *);
>  extern ssize_t proc_projid_map_write(struct file *, const char __user *, size_t, loff_t *);
> diff --git a/init/Kconfig b/init/Kconfig
> index cfee56c151f1..d4d0beeba48f 100644
> --- a/init/Kconfig
> +++ b/init/Kconfig
> @@ -1111,6 +1111,17 @@ config USER_NS
>  
>  	  If unsure, say N.
>  
> +config USER_NS_FSID
> +	bool "User namespace fsid mappings"
> +	depends on USER_NS
> +	default n
> +	help
> +	  This allows containers to alter their filesystem id mappings.
> +	  With this containers with different id mappings can still share
> +	  the same filesystem.
> +
> +	  If unsure, say N.
> +
>  config PID_NS
>  	bool "PID Namespaces"
>  	default y
> diff --git a/kernel/user.c b/kernel/user.c
> index 5235d7f49982..2ccaea9b810b 100644
> --- a/kernel/user.c
> +++ b/kernel/user.c
> @@ -55,6 +55,28 @@ struct user_namespace init_user_ns = {
>  			},
>  		},
>  	},
> +#ifdef CONFIG_USER_NS_FSID
> +	.fsuid_map = {
> +		.nr_extents = 1,
> +		{
> +			.extent[0] = {
> +				.first = 0,
> +				.lower_first = 0,
> +				.count = 4294967295U,
> +			},
> +		},
> +	},
> +	.fsgid_map = {
> +		.nr_extents = 1,
> +		{
> +			.extent[0] = {
> +				.first = 0,
> +				.lower_first = 0,
> +				.count = 4294967295U,
> +			},
> +		},
> +	},
> +#endif
>  	.count = ATOMIC_INIT(3),
>  	.owner = GLOBAL_ROOT_UID,
>  	.group = GLOBAL_ROOT_GID,
> diff --git a/kernel/user_namespace.c b/kernel/user_namespace.c
> index 8eadadc478f9..cbdf456f95f0 100644
> --- a/kernel/user_namespace.c
> +++ b/kernel/user_namespace.c
> @@ -191,6 +191,16 @@ static void free_user_ns(struct work_struct *work)
>  			kfree(ns->projid_map.forward);
>  			kfree(ns->projid_map.reverse);
>  		}
> +#ifdef CONFIG_USER_NS_FSID
> +		if (ns->fsgid_map.nr_extents > UID_GID_MAP_MAX_BASE_EXTENTS) {
> +			kfree(ns->fsgid_map.forward);
> +			kfree(ns->fsgid_map.reverse);
> +		}
> +		if (ns->fsuid_map.nr_extents > UID_GID_MAP_MAX_BASE_EXTENTS) {
> +			kfree(ns->fsuid_map.forward);
> +			kfree(ns->fsuid_map.reverse);
> +		}
> +#endif
>  		retire_userns_sysctls(ns);
>  		key_free_user_ns(ns);
>  		ns_free_inum(&ns->ns);
> @@ -637,6 +647,50 @@ static int projid_m_show(struct seq_file *seq, void *v)
>  	return 0;
>  }
>  
> +#ifdef CONFIG_USER_NS_FSID
> +static int fsuid_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;
> +
> +	lower_ns = seq_user_ns(seq);
> +	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;
> +}
> +
> +static int fsgid_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;
> +	gid_t lower;
> +
> +	lower_ns = seq_user_ns(seq);
> +	if ((lower_ns == ns) && lower_ns->parent)
> +		lower_ns = lower_ns->parent;
> +
> +	lower = from_kgid(lower_ns, KGIDT_INIT(extent->lower_first));
> +
> +	seq_printf(seq, "%10u %10u %10u\n",
> +		extent->first,
> +		lower,
> +		extent->count);
> +
> +	return 0;
> +}
> +#endif
> +
>  static void *m_start(struct seq_file *seq, loff_t *ppos,
>  		     struct uid_gid_map *map)
>  {
> @@ -674,6 +728,22 @@ static void *projid_m_start(struct seq_file *seq, loff_t *ppos)
>  	return m_start(seq, ppos, &ns->projid_map);
>  }
>  
> +#ifdef CONFIG_USER_NS_FSID
> +static void *fsuid_m_start(struct seq_file *seq, loff_t *ppos)
> +{
> +	struct user_namespace *ns = seq->private;
> +
> +	return m_start(seq, ppos, &ns->fsuid_map);
> +}
> +
> +static void *fsgid_m_start(struct seq_file *seq, loff_t *ppos)
> +{
> +	struct user_namespace *ns = seq->private;
> +
> +	return m_start(seq, ppos, &ns->fsgid_map);
> +}
> +#endif
> +
>  static void *m_next(struct seq_file *seq, void *v, loff_t *pos)
>  {
>  	(*pos)++;
> @@ -706,6 +776,22 @@ const struct seq_operations proc_projid_seq_operations = {
>  	.show = projid_m_show,
>  };
>  
> +#ifdef CONFIG_USER_NS_FSID
> +const struct seq_operations proc_fsuid_seq_operations = {
> +	.start = fsuid_m_start,
> +	.stop = m_stop,
> +	.next = m_next,
> +	.show = fsuid_m_show,
> +};
> +
> +const struct seq_operations proc_fsgid_seq_operations = {
> +	.start = fsgid_m_start,
> +	.stop = m_stop,
> +	.next = m_next,
> +	.show = fsgid_m_show,
> +};
> +#endif
> +
>  static bool mappings_overlap(struct uid_gid_map *new_map,
>  			     struct uid_gid_extent *extent)
>  {
> @@ -1081,6 +1167,42 @@ ssize_t proc_projid_map_write(struct file *file, const char __user *buf,
>  			 &ns->projid_map, &ns->parent->projid_map);
>  }
>  
> +#ifdef CONFIG_USER_NS_FSID
> +ssize_t proc_fsuid_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;
> +	struct user_namespace *seq_ns = seq_user_ns(seq);
> +
> +	if (!ns->parent)
> +		return -EPERM;
> +
> +	if ((seq_ns != ns) && (seq_ns != ns->parent))
> +		return -EPERM;
> +
> +	return map_write(file, buf, size, ppos, CAP_SETUID, &ns->fsuid_map,
> +			 &ns->parent->fsuid_map);
> +}
> +
> +ssize_t proc_fsgid_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;
> +	struct user_namespace *seq_ns = seq_user_ns(seq);
> +
> +	if (!ns->parent)
> +		return -EPERM;
> +
> +	if ((seq_ns != ns) && (seq_ns != ns->parent))
> +		return -EPERM;
> +
> +	return map_write(file, buf, size, ppos, CAP_SETGID, &ns->fsgid_map,
> +			 &ns->parent->fsgid_map);
> +}
> +#endif
> +
>  static bool new_idmap_permitted(const struct file *file,
>  				struct user_namespace *ns, int cap_setid,
>  				struct uid_gid_map *new_map)
> -- 
> 2.25.0