Re: [PATCH v2 18/25] fs: add vfs_set_fscaps()

Christian Brauner
2024-02-23T08:39:07Z

On Wed, Feb 21, 2024 at 03:24:49PM -0600, Seth Forshee (DigitalOcean) wrote:
> Provide a type-safe interface for setting filesystem capabilities and a
> generic implementation suitable for most filesystems.
>
> Signed-off-by: Seth Forshee (DigitalOcean) <sforshee@kernel.org>
> ---
> fs/xattr.c | 79 ++++++++++++++++++++++++++++++++++++++++++++++++++++++
> include/linux/fs.h | 2 ++
> 2 files changed, 81 insertions(+)
>
> diff --git a/fs/xattr.c b/fs/xattr.c
> index 10d1b1f78fc2..96de43928a51 100644
> --- a/fs/xattr.c
> +++ b/fs/xattr.c
> @@ -245,6 +245,85 @@ int vfs_get_fscaps(struct mnt_idmap *idmap, struct dentry *dentry,
> }
> EXPORT_SYMBOL(vfs_get_fscaps);
>
> +static int generic_set_fscaps(struct mnt_idmap *idmap, struct dentry *dentry,
> + const struct vfs_caps *caps, int setxattr_flags)
> +{
> + struct inode *inode = d_inode(dentry);
> + struct vfs_ns_cap_data nscaps;
> + int size;

ssize_t, I believe.

> +
> + size = vfs_caps_to_xattr(idmap, i_user_ns(inode), caps,
> + &nscaps, sizeof(nscaps));
> + if (size < 0)
> + return size;
> +
> + return __vfs_setxattr_noperm(idmap, dentry, XATTR_NAME_CAPS,
> + &nscaps, size, setxattr_flags);
> +}
> +
> +/**
> + * vfs_set_fscaps - set filesystem capabilities
> + * @idmap: idmap of the mount the inode was found from
> + * @dentry: the dentry on which to set filesystem capabilities
> + * @caps: the filesystem capabilities to be written
> + * @setxattr_flags: setxattr flags to use when writing the capabilities xattr
> + *
> + * This function writes the supplied filesystem capabilities to the dentry.
> + *
> + * Return: 0 on success, a negative errno on error.
> + */
> +int vfs_set_fscaps(struct mnt_idmap *idmap, struct dentry *dentry,
> + const struct vfs_caps *caps, int setxattr_flags)
> +{
> + struct inode *inode = d_inode(dentry);
> + struct inode *delegated_inode = NULL;
> + int error;
> +
> +retry_deleg:
> + inode_lock(inode);
> +
> + error = xattr_permission(idmap, inode, XATTR_NAME_CAPS, MAY_WRITE);
> + if (error)
> + goto out_inode_unlock;

I think this should be

/*
* We only care about restrictions the inode struct itself places upon
* us otherwise fscaps aren't subject to any VFS restrictions.
*/
error = may_write_xattr(idmap, inode);
if (error)
goto out_inode_unlock;

which is a 1:1 copy of what POSIX ACLs do?

> + error = security_inode_set_fscaps(idmap, dentry, caps, setxattr_flags);
> + if (error)
> + goto out_inode_unlock;
> +
> + error = try_break_deleg(inode, &delegated_inode);
> + if (error)
> + goto out_inode_unlock;
> +
> + if (inode->i_opflags & IOP_XATTR) {

Fwiw, I think that if we move fscaps off of xattr handlers completely
this can go away and we can simply rely on ->{g,s}et_fscaps() being
implemented. But again, that can be in a follow-up series.

> + if (inode->i_op->set_fscaps)
> + error = inode->i_op->set_fscaps(idmap, dentry, caps,
> + setxattr_flags);
> + else
> + error = generic_set_fscaps(idmap, dentry, caps,
> + setxattr_flags);
> + if (!error) {
> + fsnotify_xattr(dentry);
> + security_inode_post_set_fscaps(idmap, dentry, caps,
> + setxattr_flags);
> + }
> + } else if (unlikely(is_bad_inode(inode))) {
> + error = -EIO;
> + } else {
> + error = -EOPNOTSUPP;
> + }
> +
> +out_inode_unlock:
> + inode_unlock(inode);
> +
> + if (delegated_inode) {
> + error = break_deleg_wait(&delegated_inode);
> + if (!error)
> + goto retry_deleg;
> + }
> +
> + return error;
> +}
> +EXPORT_SYMBOL(vfs_set_fscaps);
> +
> int
> __vfs_setxattr(struct mnt_idmap *idmap, struct dentry *dentry,
> struct inode *inode, const char *name, const void *value,
> diff --git a/include/linux/fs.h b/include/linux/fs.h
> index d7cd2467e1ea..4f5d7ed44644 100644
> --- a/include/linux/fs.h
> +++ b/include/linux/fs.h
> @@ -2120,6 +2120,8 @@ extern int vfs_get_fscaps_nosec(struct mnt_idmap *idmap, struct dentry *dentry,
> struct vfs_caps *caps);
> extern int vfs_get_fscaps(struct mnt_idmap *idmap, struct dentry *dentry,
> struct vfs_caps *caps);
> +extern int vfs_set_fscaps(struct mnt_idmap *idmap, struct dentry *dentry,
> + const struct vfs_caps *caps, int setxattr_flags);

Please drop the extern.