On Tue, Feb 28, 2023 at 07:50:02PM -0600, Glenn Washburn wrote:
> Let hostfs handle idmapped mounts. This allows to have the same hostfs
> mount appear in multiple locations with different id mappings.
>
> root@(none):/media# id
> uid=0(root) gid=0(root) groups=0(root)
> root@(none):/media# mkdir mnt idmapped
> root@(none):/media# mount -thostfs -o/home/user hostfs mnt
>
> root@(none):/media# touch mnt/aaa
> root@(none):/media# mount-idmapped --map-mount u:`id -u user`:0:1 --map-mount g:`id -g user`:0:1 /media/mnt /media/idmapped
> root@(none):/media# ls -l mnt/aaa idmapped/aaa
> -rw-r--r-- 1 root root 0 Jan 28 01:23 idmapped/aaa
> -rw-r--r-- 1 user user 0 Jan 28 01:23 mnt/aaa
>
> root@(none):/media# touch idmapped/bbb
> root@(none):/media# ls -l mnt/bbb idmapped/bbb
> -rw-r--r-- 1 root root 0 Jan 28 01:26 idmapped/bbb
> -rw-r--r-- 1 user user 0 Jan 28 01:26 mnt/bbb
>
> Signed-off-by: Glenn Washburn <development@xxxxxxxxxxxxxxx>
> ---
> Changes from v1:
> * Rebase on to tip. The above commands work and have the results expected.
> The __vfsuid_val(make_vfsuid(...)) seems ugly to get the uid_t, but it
> seemed like the best one I've come across. Is there a better way?
Sure, I can help you with that. ;)
>
> Glenn
> ---
> fs/hostfs/hostfs_kern.c | 13 +++++++------
> 1 file changed, 7 insertions(+), 6 deletions(-)
>
> diff --git a/fs/hostfs/hostfs_kern.c b/fs/hostfs/hostfs_kern.c
> index c18bb50c31b6..9459da99a0db 100644
> --- a/fs/hostfs/hostfs_kern.c
> +++ b/fs/hostfs/hostfs_kern.c
> @@ -786,7 +786,7 @@ static int hostfs_permission(struct mnt_idmap *idmap,
> err = access_file(name, r, w, x);
> __putname(name);
> if (!err)
> - err = generic_permission(&nop_mnt_idmap, ino, desired);
> + err = generic_permission(idmap, ino, desired);
> return err;
> }
>
> @@ -794,13 +794,14 @@ static int hostfs_setattr(struct mnt_idmap *idmap,
> struct dentry *dentry, struct iattr *attr)
> {
> struct inode *inode = d_inode(dentry);
> + struct user_namespace *fs_userns = i_user_ns(inode);
Fyi, since hostfs can't be mounted in a user namespace
fs_userns == &init_user_ns
so it doesn't really matter what you use.
> struct hostfs_iattr attrs;
> char *name;
> int err;
>
> int fd = HOSTFS_I(inode)->fd;
>
> - err = setattr_prepare(&nop_mnt_idmap, dentry, attr);
> + err = setattr_prepare(idmap, dentry, attr);
> if (err)
> return err;
>
> @@ -814,11 +815,11 @@ static int hostfs_setattr(struct mnt_idmap *idmap,
> }
> if (attr->ia_valid & ATTR_UID) {
> attrs.ia_valid |= HOSTFS_ATTR_UID;
> - attrs.ia_uid = from_kuid(&init_user_ns, attr->ia_uid);
> + attrs.ia_uid = __vfsuid_val(make_vfsuid(idmap, fs_userns, attr->ia_uid));
> }
> if (attr->ia_valid & ATTR_GID) {
> attrs.ia_valid |= HOSTFS_ATTR_GID;
> - attrs.ia_gid = from_kgid(&init_user_ns, attr->ia_gid);
> + attrs.ia_gid = __vfsgid_val(make_vfsgid(idmap, fs_userns, attr->ia_gid));
Heh, if you look include/linux/fs.h:
/*
* The two anonymous unions wrap structures with the same member.
*
* Filesystems raising FS_ALLOW_IDMAP need to use ia_vfs{g,u}id which
* are a dedicated type requiring the filesystem to use the dedicated
* helpers. Other filesystem can continue to use ia_{g,u}id until they
* have been ported.
*
* They always contain the same value. In other words FS_ALLOW_IDMAP
* pass down the same value on idmapped mounts as they would on regular
* mounts.
*/
union {
kuid_t ia_uid;
vfsuid_t ia_vfsuid;
};
union {
kgid_t ia_gid;
vfsgid_t ia_vfsgid;
};
this just is:
attrs.ia_uid = from_vfsuid(idmap, fs_userns, attr->ia_vfsuid));
attrs.ia_gid = from_vfsgid(idmap, fs_userns, attr->ia_vfsgid));
(I plan to fully replace ia_{g,u}id at some point.)
Christian
