[PATCH v2 20/25] ovl: add fscaps handlers

[Amir Goldstein]

On Wed, Feb 21, 2024 at 11:25 PM Seth Forshee (DigitalOcean)
<sforshee at kernel.org> wrote:
>
> Add handlers which read fs caps from the lower or upper filesystem and
> write/remove fs caps to the upper filesystem, performing copy-up as
> necessary.
>
> While fscaps only really make sense on regular files, the general policy
> is to allow most xattr namespaces on all different inode types, so
> fscaps handlers are installed in the inode operations for all types of
> inodes.
>
> Signed-off-by: Seth Forshee (DigitalOcean) <sforshee at kernel.org>
> ---
>  fs/overlayfs/dir.c       |  2 ++
>  fs/overlayfs/inode.c     | 72 ++++++++++++++++++++++++++++++++++++++++++++++++
>  fs/overlayfs/overlayfs.h |  5 ++++
>  3 files changed, 79 insertions(+)
>
> diff --git a/fs/overlayfs/dir.c b/fs/overlayfs/dir.c
> index 0f8b4a719237..4ff360fe10c9 100644
> --- a/fs/overlayfs/dir.c
> +++ b/fs/overlayfs/dir.c
> @@ -1307,6 +1307,8 @@ const struct inode_operations ovl_dir_inode_operations = {
>         .get_inode_acl  = ovl_get_inode_acl,
>         .get_acl        = ovl_get_acl,
>         .set_acl        = ovl_set_acl,
> +       .get_fscaps     = ovl_get_fscaps,
> +       .set_fscaps     = ovl_set_fscaps,
>         .update_time    = ovl_update_time,
>         .fileattr_get   = ovl_fileattr_get,
>         .fileattr_set   = ovl_fileattr_set,
> diff --git a/fs/overlayfs/inode.c b/fs/overlayfs/inode.c
> index c63b31a460be..7a8978ea6fe1 100644
> --- a/fs/overlayfs/inode.c
> +++ b/fs/overlayfs/inode.c
> @@ -568,6 +568,72 @@ int ovl_set_acl(struct mnt_idmap *idmap, struct dentry *dentry,
>  }
>  #endif
>
> +int ovl_get_fscaps(struct mnt_idmap *idmap, struct dentry *dentry,
> +                  struct vfs_caps *caps)
> +{
> +       int err;
> +       const struct cred *old_cred;
> +       struct path realpath;
> +
> +       ovl_path_real(dentry, &realpath);
> +       old_cred = ovl_override_creds(dentry->d_sb);
> +       err = vfs_get_fscaps(mnt_idmap(realpath.mnt), realpath.dentry, caps);
> +       revert_creds(old_cred);
> +       return err;
> +}
> +
> +int ovl_set_fscaps(struct mnt_idmap *idmap, struct dentry *dentry,
> +                  const struct vfs_caps *caps, int setxattr_flags)
> +{
> +       int err;
> +       struct ovl_fs *ofs = OVL_FS(dentry->d_sb);
> +       struct dentry *upperdentry = ovl_dentry_upper(dentry);
> +       struct dentry *realdentry = upperdentry ?: ovl_dentry_lower(dentry);
> +       const struct cred *old_cred;
> +
> +       /*
> +        * If the fscaps are to be remove from a lower file, check that they
> +        * exist before copying up.
> +        */

Don't you need to convert -ENODATA to 0 return value in this case?

> +       if (!caps && !upperdentry) {
> +               struct path realpath;
> +               struct vfs_caps lower_caps;
> +
> +               ovl_path_lower(dentry, &realpath);
> +               old_cred = ovl_override_creds(dentry->d_sb);
> +               err = vfs_get_fscaps(mnt_idmap(realpath.mnt), realdentry,
> +                                    &lower_caps);
> +               revert_creds(old_cred);
> +               if (err)
> +                       goto out;
> +       }
> +
> +       err = ovl_want_write(dentry);
> +       if (err)
> +               goto out;
> +

ovl_want_write() should after ovl_copy_up(), see:
162d06444070 ("ovl: reorder ovl_want_write() after ovl_inode_lock()")


> +       err = ovl_copy_up(dentry);
> +       if (err)
> +               goto out_drop_write;
> +       upperdentry = ovl_dentry_upper(dentry);
> +
> +       old_cred = ovl_override_creds(dentry->d_sb);
> +       if (!caps)
> +               err = vfs_remove_fscaps(ovl_upper_mnt_idmap(ofs), upperdentry);
> +       else
> +               err = vfs_set_fscaps(ovl_upper_mnt_idmap(ofs), upperdentry,
> +                                    caps, setxattr_flags);
> +       revert_creds(old_cred);
> +
> +       /* copy c/mtime */
> +       ovl_copyattr(d_inode(dentry));
> +
> +out_drop_write:
> +       ovl_drop_write(dentry);
> +out:
> +       return err;
> +}
> +
>  int ovl_update_time(struct inode *inode, int flags)
>  {
>         if (flags & S_ATIME) {
> @@ -747,6 +813,8 @@ static const struct inode_operations ovl_file_inode_operations = {
>         .get_inode_acl  = ovl_get_inode_acl,
>         .get_acl        = ovl_get_acl,
>         .set_acl        = ovl_set_acl,
> +       .get_fscaps     = ovl_get_fscaps,
> +       .set_fscaps     = ovl_set_fscaps,
>         .update_time    = ovl_update_time,
>         .fiemap         = ovl_fiemap,
>         .fileattr_get   = ovl_fileattr_get,
> @@ -758,6 +826,8 @@ static const struct inode_operations ovl_symlink_inode_operations = {
>         .get_link       = ovl_get_link,
>         .getattr        = ovl_getattr,
>         .listxattr      = ovl_listxattr,
> +       .get_fscaps     = ovl_get_fscaps,
> +       .set_fscaps     = ovl_set_fscaps,
>         .update_time    = ovl_update_time,
>  };
>
> @@ -769,6 +839,8 @@ static const struct inode_operations ovl_special_inode_operations = {
>         .get_inode_acl  = ovl_get_inode_acl,
>         .get_acl        = ovl_get_acl,
>         .set_acl        = ovl_set_acl,
> +       .get_fscaps     = ovl_get_fscaps,
> +       .set_fscaps     = ovl_set_fscaps,
>         .update_time    = ovl_update_time,
>  };
>


Sorry, I did not understand the explanation why fscaps ops are needed
for non regular files. It does not look right to me.

Thanks,
Amir.