Re: [PATCH v23 14/22] richacl: Update the file masks in chmod()

[Jeff Layton <jlayton-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org>]

On Thu, 2016-06-30 at 15:47 +0200, Andreas Gruenbacher wrote:
> Doing a chmod() sets the file mode, which includes the file permission
> bits.  When a file has a richacl, the permissions that the richacl
> grants need to be limited to what the new file permission bits allow.
> 
> This is done by setting the file masks in the richacl to what the file
> permission bits map to.  The richacl access check algorithm takes the
> file masks into account, which ensures that the richacl cannot grant too
> many permissions.
> 
> It is possible to explicitly add permissions to the file masks which go
> beyond what the file permission bits can grant (like the
> RICHACE_WRITE_ACL permission).  The POSIX.1 standard calls this an
> alternate file access control mechanism.  A subsequent chmod() would
> ensure that those permissions are disabled again.
> 
> Signed-off-by: Andreas Gruenbacher <agruenba-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org>
> Reviewed-by: J. Bruce Fields <bfields-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org>
> ---
>  fs/richacl.c            | 71 +++++++++++++++++++++++++++++++++++++++++++++++++
>  include/linux/richacl.h |  1 +
>  2 files changed, 72 insertions(+)
> 
> diff --git a/fs/richacl.c b/fs/richacl.c
> index b2a03c1..ba110a6 100644
> --- a/fs/richacl.c
> +++ b/fs/richacl.c
> @@ -547,3 +547,74 @@ out:
>  	return denied ? -EACCES : 0;
>  }
>  EXPORT_SYMBOL_GPL(richacl_permission);
> +
> +/**
> + * __richacl_chmod  -  update the file masks to reflect the new mode
> + * @acl:	access control list
> + * @mode:	new file permission bits including the file type
> + *
> + * Return a copy of @acl where the file masks have been replaced by the file
> + * masks corresponding to the file permission bits in @mode, or returns @acl
> + * itself if the file masks are already up to date.  Takes over a reference
> + * to @acl.
> + */
> +static struct richacl *
> +__richacl_chmod(struct richacl *acl, umode_t mode)
> +{
> +	unsigned int x = S_ISDIR(mode) ? 0 : RICHACE_DELETE_CHILD;
> +	unsigned int owner_mask, group_mask, other_mask;
> +	struct richacl *clone;
> +
> +	owner_mask = richacl_mode_to_mask(mode >> 6) & ~x;
> +	group_mask = richacl_mode_to_mask(mode >> 3) & ~x;
> +	other_mask = richacl_mode_to_mask(mode)      & ~x;
> +
> +	if (acl->a_owner_mask == owner_mask &&
> +	    acl->a_group_mask == group_mask &&
> +	    acl->a_other_mask == other_mask &&
> +	    (acl->a_flags & RICHACL_MASKED) &&
> +	    (acl->a_flags & RICHACL_WRITE_THROUGH))
> +		return acl;
> +
> +	clone = richacl_clone(acl, GFP_KERNEL);
> +	richacl_put(acl);
> +	if (!clone)
> +		return ERR_PTR(-ENOMEM);
> +
> +	clone->a_flags |= (RICHACL_WRITE_THROUGH | RICHACL_MASKED);
> +	clone->a_owner_mask = owner_mask;
> +	clone->a_group_mask = group_mask;
> +	clone->a_other_mask = other_mask;
> +
> +	return clone;
> +}
> +
> +/**
> + * richacl_chmod  -  filesystem chmod helper
> + * @inode:	inode whose file permission bits to change
> + * @mode:	new file permission bits including the file type
> + *
> + * Helper for filesystems to use to perform a chmod on the richacl of an inode.
> + */
> +int
> +richacl_chmod(struct inode *inode, umode_t mode)
> +{
> +	struct richacl *acl;
> +	int retval;
> +
> +	if (S_ISLNK(mode))
> +		return -EOPNOTSUPP;
> +	if (!inode->i_op->set_richacl)
> +		return -EOPNOTSUPP;
> +	acl = get_richacl(inode);
> +	if (IS_ERR_OR_NULL(acl))
> +		return PTR_ERR(acl);
> +	acl = __richacl_chmod(acl, mode);
> +	if (IS_ERR(acl))
> +		return PTR_ERR(acl);
> +	retval = inode->i_op->set_richacl(inode, acl);
> +	richacl_put(acl);
> +
> +	return retval;
> +}
> +EXPORT_SYMBOL(richacl_chmod);
> diff --git a/include/linux/richacl.h b/include/linux/richacl.h
> index 3e05c94..db82fab 100644
> --- a/include/linux/richacl.h
> +++ b/include/linux/richacl.h
> @@ -190,5 +190,6 @@ extern unsigned int richacl_mode_to_mask(umode_t);
>  extern unsigned int richacl_want_to_mask(unsigned int);
>  extern void richacl_compute_max_masks(struct richacl *);
>  extern int richacl_permission(struct inode *, const struct richacl *, int);
> +extern int richacl_chmod(struct inode *, umode_t);
>  
>  #endif /* __RICHACL_H */

Acked-by: Jeff Layton <jlayton-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org>