Re: [PATCH 01/10] fs: add is_mapped_mnt() helper

[Amir Goldstein <amir73il@gmail.com>]

On Tue, Nov 23, 2021 at 2:18 PM Christian Brauner <brauner@kernel.org> wrote:
>
> From: Christian Brauner <christian.brauner@ubuntu.com>
>
> Multiple places open-code the same check to determine whether a given
> mount is idmapped. Introduce a simple helper function that can be used
> instead. This allows us to get rid of the fragile open-coding. We will
> later change the check that is used to determine whether a given mount
> is idmapped. Introducing a helper allows us to do this in a single
> place instead of doing it for multiple places.
>
> Cc: Seth Forshee <sforshee@digitalocean.com>
> Cc: Christoph Hellwig <hch@lst.de>
> Cc: Al Viro <viro@zeniv.linux.org.uk>
> CC: linux-fsdevel@vger.kernel.org
> Signed-off-by: Christian Brauner <christian.brauner@ubuntu.com>
> ---
>  fs/cachefiles/bind.c |  2 +-
>  fs/ecryptfs/main.c   |  2 +-
>  fs/namespace.c       |  2 +-
>  fs/nfsd/export.c     |  2 +-
>  fs/overlayfs/super.c |  2 +-
>  fs/proc_namespace.c  |  2 +-
>  include/linux/fs.h   | 14 ++++++++++++++
>  7 files changed, 20 insertions(+), 6 deletions(-)
>
> diff --git a/fs/cachefiles/bind.c b/fs/cachefiles/bind.c
> index d463d89f5db8..8130142d89c2 100644
> --- a/fs/cachefiles/bind.c
> +++ b/fs/cachefiles/bind.c
> @@ -117,7 +117,7 @@ static int cachefiles_daemon_add_cache(struct cachefiles_cache *cache)
>         root = path.dentry;
>
>         ret = -EINVAL;
> -       if (mnt_user_ns(path.mnt) != &init_user_ns) {
> +       if (is_mapped_mnt(path.mnt)) {
>                 pr_warn("File cache on idmapped mounts not supported");
>                 goto error_unsupported;
>         }
> diff --git a/fs/ecryptfs/main.c b/fs/ecryptfs/main.c
> index d66bbd2df191..331ac3a59515 100644
> --- a/fs/ecryptfs/main.c
> +++ b/fs/ecryptfs/main.c
> @@ -537,7 +537,7 @@ static struct dentry *ecryptfs_mount(struct file_system_type *fs_type, int flags
>                 goto out_free;
>         }
>
> -       if (mnt_user_ns(path.mnt) != &init_user_ns) {
> +       if (is_mapped_mnt(path.mnt)) {
>                 rc = -EINVAL;
>                 printk(KERN_ERR "Mounting on idmapped mounts currently disallowed\n");
>                 goto out_free;
> diff --git a/fs/namespace.c b/fs/namespace.c
> index 659a8f39c61a..7d7b80b375a4 100644
> --- a/fs/namespace.c
> +++ b/fs/namespace.c
> @@ -3936,7 +3936,7 @@ static int can_idmap_mount(const struct mount_kattr *kattr, struct mount *mnt)
>          * mapping. It makes things simpler and callers can just create
>          * another bind-mount they can idmap if they want to.
>          */
> -       if (mnt_user_ns(m) != &init_user_ns)
> +       if (is_mapped_mnt(m))
>                 return -EPERM;
>
>         /* The underlying filesystem doesn't support idmapped mounts yet. */
> diff --git a/fs/nfsd/export.c b/fs/nfsd/export.c
> index 9421dae22737..292bde9e1eb3 100644
> --- a/fs/nfsd/export.c
> +++ b/fs/nfsd/export.c
> @@ -427,7 +427,7 @@ static int check_export(struct path *path, int *flags, unsigned char *uuid)
>                 return -EINVAL;
>         }
>
> -       if (mnt_user_ns(path->mnt) != &init_user_ns) {
> +       if (is_mapped_mnt(path->mnt)) {
>                 dprintk("exp_export: export of idmapped mounts not yet supported.\n");
>                 return -EINVAL;
>         }
> diff --git a/fs/overlayfs/super.c b/fs/overlayfs/super.c
> index 265181c110ae..113575fc6155 100644
> --- a/fs/overlayfs/super.c
> +++ b/fs/overlayfs/super.c
> @@ -873,7 +873,7 @@ static int ovl_mount_dir_noesc(const char *name, struct path *path)
>                 pr_err("filesystem on '%s' not supported\n", name);
>                 goto out_put;
>         }
> -       if (mnt_user_ns(path->mnt) != &init_user_ns) {
> +       if (is_mapped_mnt(path->mnt)) {
>                 pr_err("idmapped layers are currently not supported\n");
>                 goto out_put;
>         }
> diff --git a/fs/proc_namespace.c b/fs/proc_namespace.c
> index 392ef5162655..788c687bb052 100644
> --- a/fs/proc_namespace.c
> +++ b/fs/proc_namespace.c
> @@ -80,7 +80,7 @@ static void show_mnt_opts(struct seq_file *m, struct vfsmount *mnt)
>                         seq_puts(m, fs_infop->str);
>         }
>
> -       if (mnt_user_ns(mnt) != &init_user_ns)
> +       if (is_mapped_mnt(mnt))
>                 seq_puts(m, ",idmapped");
>  }
>
> diff --git a/include/linux/fs.h b/include/linux/fs.h
> index 1cb616fc1105..192242476b2b 100644
> --- a/include/linux/fs.h
> +++ b/include/linux/fs.h
> @@ -2725,6 +2725,20 @@ static inline struct user_namespace *file_mnt_user_ns(struct file *file)
>  {
>         return mnt_user_ns(file->f_path.mnt);
>  }
> +
> +/**
> + * is_mapped_mnt - check whether a mount is mapped
> + * @mnt: the mount to check
> + *
> + * If @mnt has an idmapping attached to it @mnt is mapped.
> + *
> + * Return: true if mount is mapped, false if not.
> + */
> +static inline bool is_mapped_mnt(const struct vfsmount *mnt)
> +{
> +       return mnt_user_ns(mnt) != &init_user_ns;
> +}
> +

Maybe is_idmapped_mnt?

Thanks,
Amir.