On Tue, Jul 27, 2021 at 12:48:40PM +0200, Christian Brauner wrote:
> From: Christian Brauner <christian.brauner@xxxxxxxxxx>
>
> Various filesystems rely on the lookup_one_len() helper to lookup a single path
> component relative to a well-known starting point. Allow such filesystems to
> support idmapped mounts by adding a version of this helper to take the idmap
> into account when calling inode_permission(). This change is a required to let
> btrfs (and other filesystems) support idmapped mounts.
>
> Cc: Christoph Hellwig <hch@xxxxxxxxxxxxx>
> Cc: Al Viro <viro@xxxxxxxxxxxxxxxxxx>
> Cc: Matthew Wilcox (Oracle) <willy@xxxxxxxxxxxxx>
> Cc: linux-fsdevel@xxxxxxxxxxxxxxx
> Reviewed-by: Josef Bacik <josef@xxxxxxxxxxxxxx>
> Signed-off-by: Christian Brauner <christian.brauner@xxxxxxxxxx>
> ---
Christoph, Matthew are you ok with this now?
Christian
> /* v2 */
> - Al Viro <viro@xxxxxxxxxxxxxxxxxx>:
> - Add a new lookup helper instead of changing the old ones.
>
> /* v3 */
> unchanged
>
> /* v4 */
> - Christoph Hellwig <hch@xxxxxxxxxxxxx>,
> Matthew Wilcox (Oracle) <willy@xxxxxxxxxxxxx>:
> - Simplify the name of lookup_mapped_one_len() to either lookup_one_mapped()
> or lookup_one(). The *_len() prefix in all those helper apparently just
> exists for historical reasons because we used to have lookup_dentry(), then
> grew lookup_one(), and then grew lookup_one_len().
> ---
> fs/namei.c | 43 +++++++++++++++++++++++++++++++++++++------
> include/linux/namei.h | 2 ++
> 2 files changed, 39 insertions(+), 6 deletions(-)
>
> diff --git a/fs/namei.c b/fs/namei.c
> index bf6d8a738c59..902df46e7dd3 100644
> --- a/fs/namei.c
> +++ b/fs/namei.c
> @@ -2575,8 +2575,9 @@ int vfs_path_lookup(struct dentry *dentry, struct vfsmount *mnt,
> }
> EXPORT_SYMBOL(vfs_path_lookup);
>
> -static int lookup_one_len_common(const char *name, struct dentry *base,
> - int len, struct qstr *this)
> +static int lookup_one_common(struct user_namespace *mnt_userns,
> + const char *name, struct dentry *base, int len,
> + struct qstr *this)
> {
> this->name = name;
> this->len = len;
> @@ -2604,7 +2605,7 @@ static int lookup_one_len_common(const char *name, struct dentry *base,
> return err;
> }
>
> - return inode_permission(&init_user_ns, base->d_inode, MAY_EXEC);
> + return inode_permission(mnt_userns, base->d_inode, MAY_EXEC);
> }
>
> /**
> @@ -2628,7 +2629,7 @@ struct dentry *try_lookup_one_len(const char *name, struct dentry *base, int len
>
> WARN_ON_ONCE(!inode_is_locked(base->d_inode));
>
> - err = lookup_one_len_common(name, base, len, &this);
> + err = lookup_one_common(&init_user_ns, name, base, len, &this);
> if (err)
> return ERR_PTR(err);
>
> @@ -2655,7 +2656,7 @@ struct dentry *lookup_one_len(const char *name, struct dentry *base, int len)
>
> WARN_ON_ONCE(!inode_is_locked(base->d_inode));
>
> - err = lookup_one_len_common(name, base, len, &this);
> + err = lookup_one_common(&init_user_ns, name, base, len, &this);
> if (err)
> return ERR_PTR(err);
>
> @@ -2664,6 +2665,36 @@ struct dentry *lookup_one_len(const char *name, struct dentry *base, int len)
> }
> EXPORT_SYMBOL(lookup_one_len);
>
> +/**
> + * lookup_one - filesystem helper to lookup single pathname component
> + * @mnt_userns: user namespace of the mount the lookup is performed from
> + * @name: pathname component to lookup
> + * @base: base directory to lookup from
> + * @len: maximum length @len should be interpreted to
> + *
> + * Note that this routine is purely a helper for filesystem usage and should
> + * not be called by generic code.
> + *
> + * The caller must hold base->i_mutex.
> + */
> +struct dentry *lookup_one(struct user_namespace *mnt_userns, const char *name,
> + struct dentry *base, int len)
> +{
> + struct dentry *dentry;
> + struct qstr this;
> + int err;
> +
> + WARN_ON_ONCE(!inode_is_locked(base->d_inode));
> +
> + err = lookup_one_common(mnt_userns, name, base, len, &this);
> + if (err)
> + return ERR_PTR(err);
> +
> + dentry = lookup_dcache(&this, base, 0);
> + return dentry ? dentry : __lookup_slow(&this, base, 0);
> +}
> +EXPORT_SYMBOL(lookup_one);
> +
> /**
> * lookup_one_len_unlocked - filesystem helper to lookup single pathname component
> * @name: pathname component to lookup
> @@ -2683,7 +2714,7 @@ struct dentry *lookup_one_len_unlocked(const char *name,
> int err;
> struct dentry *ret;
>
> - err = lookup_one_len_common(name, base, len, &this);
> + err = lookup_one_common(&init_user_ns, name, base, len, &this);
> if (err)
> return ERR_PTR(err);
>
> diff --git a/include/linux/namei.h b/include/linux/namei.h
> index be9a2b349ca7..df106b6d3cc5 100644
> --- a/include/linux/namei.h
> +++ b/include/linux/namei.h
> @@ -68,6 +68,8 @@ extern struct dentry *try_lookup_one_len(const char *, struct dentry *, int);
> extern struct dentry *lookup_one_len(const char *, struct dentry *, int);
> extern struct dentry *lookup_one_len_unlocked(const char *, struct dentry *, int);
> extern struct dentry *lookup_positive_unlocked(const char *, struct dentry *, int);
> +extern struct dentry *lookup_one(struct user_namespace *, const char *,
> + struct dentry *, int);
>
> extern int follow_down_one(struct path *);
> extern int follow_down(struct path *);
> --
> 2.30.2
>
