Re: [PATCH v2 01/10] fs: add is_idmapped_mnt() helper

Seth Forshee
2021-12-02T17:09:55Z

On Tue, Nov 30, 2021 at 01:10:23PM +0100, Christian Brauner 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.
>
> Link: https://lore.kernel.org/r/20211123114227.3124056-2-brauner@kernel.org (v1)
> Cc: Seth Forshee <sforshee@digitalocean.com>
> Cc: Amir Goldstein <amir73il@gmail.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>

Reviewed-by: Seth Forshee <sforshee@digitalocean.com>

> ---
> /* v2 */
> - Amir Goldstein <amir73il@gmail.com>:
> - s/is_mapped_mnt/is_idmapped_mnt/g
> ---
> 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..146291be6263 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_idmapped_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..2dd23a82e0de 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_idmapped_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..4994b816a74c 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_idmapped_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..668c7527b17e 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_idmapped_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..7bb0a47cb615 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_idmapped_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..49650e54d2f8 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_idmapped_mnt(mnt))
> seq_puts(m, ",idmapped");
> }
>
> diff --git a/include/linux/fs.h b/include/linux/fs.h
> index 1cb616fc1105..426cc7bcbeb8 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_idmapped_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_idmapped_mnt(const struct vfsmount *mnt)
> +{
> + return mnt_user_ns(mnt) != &init_user_ns;
> +}
> +
> extern long vfs_truncate(const struct path *, loff_t);
> int do_truncate(struct user_namespace *, struct dentry *, loff_t start,
> unsigned int time_attrs, struct file *filp);
> --
> 2.30.2
>