On Thu, Jan 21, 2021 at 02:19:21PM +0100, Christian Brauner wrote:
> Add simple helpers to make it easy to map kuids into and from idmapped
> mounts. We provide simple wrappers that filesystems can use to e.g.
> initialize inodes similar to i_{uid,gid}_read() and i_{uid,gid}_write().
> Accessing an inode through an idmapped mount maps the i_uid and i_gid of
> the inode to the mount's user namespace. If the fsids are used to
> initialize inodes they are unmapped according to the mount's user
> namespace. Passing the initial user namespace to these helpers makes
> them a nop and so any non-idmapped paths will not be impacted.
>
> Link: https://lore.kernel.org/r/20210112220124.837960-9-christian.brauner@xxxxxxxxxx
> Cc: David Howells <dhowells@xxxxxxxxxx>
> Cc: Al Viro <viro@xxxxxxxxxxxxxxxxxx>
> Cc: linux-fsdevel@xxxxxxxxxxxxxxx
> Reviewed-by: Christoph Hellwig <hch@xxxxxx>
> Signed-off-by: Christian Brauner <christian.brauner@xxxxxxxxxx>
> ---
> /* v2 */
> - Christoph Hellwig <hch@xxxxxx>:
> - Get rid of the ifdefs and the config option that hid idmapped mounts.
>
> /* v3 */
> unchanged
>
> /* v4 */
> - Serge Hallyn <serge@xxxxxxxxxx>:
> - Use "mnt_userns" to refer to a vfsmount's userns everywhere to make
> terminology consistent.
>
> /* v5 */
> unchanged
> base-commit: 7c53f6b671f4aba70ff15e1b05148b10d58c2837
>
> /* v6 */
> unchanged
> base-commit: 19c329f6808995b142b3966301f217c831e7cf31
> ---
> include/linux/fs.h | 47 ++++++++++++++++++++++++++++++++++++++++++++++
> 1 file changed, 47 insertions(+)
>
> diff --git a/include/linux/fs.h b/include/linux/fs.h
> index fd0b80e6361d..3165998e2294 100644
> --- a/include/linux/fs.h
> +++ b/include/linux/fs.h
> @@ -40,6 +40,7 @@
> #include <linux/build_bug.h>
> #include <linux/stddef.h>
> #include <linux/mount.h>
> +#include <linux/cred.h>
>
> #include <asm/byteorder.h>
> #include <uapi/linux/fs.h>
> @@ -1573,6 +1574,52 @@ static inline void i_gid_write(struct inode *inode, gid_t gid)
> inode->i_gid = make_kgid(inode->i_sb->s_user_ns, gid);
> }
>
> +static inline kuid_t kuid_into_mnt(struct user_namespace *mnt_userns,
> + kuid_t kuid)
> +{
> + return make_kuid(mnt_userns, __kuid_val(kuid));
> +}
> +
Hi Christian,
I am having little trouble w.r.t function names and trying to figure
out whether they are mapping id down or up.
For example, kuid_into_mnt() ultimately calls map_id_down(). That is,
id visible inside user namespace is mapped to host
(if observer is in init_user_ns, IIUC).
But fsuid_into_mnt() ultimately calls map_id_up(). That's take a kuid
and map it into the user_namespace.
So both the helpers end with into_mnt() but one maps id down and
other maps id up. I found this confusing and was wondering how
should I visualize it. So thought of asking you.
Is this intentional or can naming be improved so that *_into_mnt()
means one thing (Either map_id_up() or map_id_down()). And vice-a-versa
for *_from_mnt().
Thanks
Vivek
> +static inline kgid_t kgid_into_mnt(struct user_namespace *mnt_userns,
> + kgid_t kgid)
> +{
> + return make_kgid(mnt_userns, __kgid_val(kgid));
> +}
> +
> +static inline kuid_t i_uid_into_mnt(struct user_namespace *mnt_userns,
> + const struct inode *inode)
> +{
> + return kuid_into_mnt(mnt_userns, inode->i_uid);
> +}
> +
> +static inline kgid_t i_gid_into_mnt(struct user_namespace *mnt_userns,
> + const struct inode *inode)
> +{
> + return kgid_into_mnt(mnt_userns, inode->i_gid);
> +}
> +
> +static inline kuid_t kuid_from_mnt(struct user_namespace *mnt_userns,
> + kuid_t kuid)
> +{
> + return KUIDT_INIT(from_kuid(mnt_userns, kuid));
> +}
> +
> +static inline kgid_t kgid_from_mnt(struct user_namespace *mnt_userns,
> + kgid_t kgid)
> +{
> + return KGIDT_INIT(from_kgid(mnt_userns, kgid));
> +}
> +
> +static inline kuid_t fsuid_into_mnt(struct user_namespace *mnt_userns)
> +{
> + return kuid_from_mnt(mnt_userns, current_fsuid());
> +}
> +
> +static inline kgid_t fsgid_into_mnt(struct user_namespace *mnt_userns)
> +{
> + return kgid_from_mnt(mnt_userns, current_fsgid());
> +}
> +
> extern struct timespec64 current_time(struct inode *inode);
>
> /*
> --
> 2.30.0
>
