Re: [RFC v7 26/41] richacl: Apply the file masks to a richacl

[J. Bruce Fields]

On Sat, Sep 05, 2015 at 12:27:21PM +0200, Andreas Gruenbacher wrote:
> Put all the pieces of the acl transformation puzzle together for
> computing a richacl which has the file masks "applied" so that the
> standard nfsv4 access check algorithm can be used on the richacl.
> 
> Signed-off-by: Andreas Gruenbacher <agruen@xxxxxxxxxx>
> ---
>  fs/richacl_compat.c     | 110 ++++++++++++++++++++++++++++++++++++++++++++++++
>  include/linux/richacl.h |   3 ++
>  2 files changed, 113 insertions(+)
> 
> diff --git a/fs/richacl_compat.c b/fs/richacl_compat.c
> index 412844c..9681efe 100644
> --- a/fs/richacl_compat.c
> +++ b/fs/richacl_compat.c
> @@ -730,3 +730,113 @@ richacl_isolate_group_class(struct richacl_alloc *alloc)
>  	}
>  	return 0;
>  }
> +
> +/**
> + * __richacl_apply_masks  -  apply the file masks to all aces
> + * @alloc:	acl and number of allocated entries
> + *
> + * Apply the owner mask to owner@ aces, the other mask to
> + * everyone@ aces, and the group mask to all other aces.
> + *
> + * The previous transformations have brought the acl into a
> + * form in which applying the masks will not lead to the
> + * accidental loss of permissions anymore.
> + */
> +static int
> +__richacl_apply_masks(struct richacl_alloc *alloc, kuid_t owner)
> +{
> +	struct richace *ace;
> +
> +	richacl_for_each_entry(ace, alloc->acl) {
> +		unsigned int mask;
> +
> +		if (richace_is_inherit_only(ace) || !richace_is_allow(ace))
> +			continue;
> +		if (richace_is_owner(ace) ||
> +		    (richace_is_unix_user(ace) && uid_eq(owner, ace->e_id.uid)))
> +			mask = alloc->acl->a_owner_mask;

Is treating matching user aces like owner aces what you intended to do,
and if so, why?

--b.

> +		else if (richace_is_everyone(ace))
> +			mask = alloc->acl->a_other_mask;
> +		else
> +			mask = alloc->acl->a_group_mask;
> +		if (richace_change_mask(alloc, &ace, ace->e_mask & mask))
> +			return -1;
> +	}
> +	return 0;
> +}
> +
> +/**
> + * richacl_apply_masks  -  apply the masks to the acl
> + *
> + * Transform @acl so that the standard NFSv4 permission check algorithm (which
> + * is not aware of file masks) will compute the same access decisions as the
> + * richacl permission check algorithm (which looks at the acl and the file
> + * masks).
> + *
> + * This algorithm is split into several steps:
> + *
> + *   - Move everyone@ aces to the end of the acl.  This simplifies the other
> + *     transformations, and allows the everyone@ allow ace at the end of the
> + *     acl to eventually allow permissions to the other class only.
> + *
> + *   - Propagate everyone@ permissions up the acl.  This transformation makes
> + *     sure that the owner and group class aces won't lose any permissions when
> + *     we apply the other mask to the everyone@ allow ace at the end of the acl.
> + *
> + *   - Apply the file masks to all aces.
> + *
> + *   - Make sure the owner is granted the owner mask permissions.
> + *
> + *   - Make sure everyone is granted the other mask permissions.
> + *
> + *   - Make sure that the owner is not granted any permissions beyond the owner
> + *     mask from group class aces or from everyone@.
> + *
> + *   - Make sure that the group class is not granted any permissions from
> + *     everyone@.
> + *
> + * The algorithm is exact except for richacls which cannot be represented as an
> + * acl alone: for example, given this acl:
> + *
> + *    group@:rw::allow
> + *
> + * when file masks corresponding to mode 0600 are applied, the owner would only
> + * get rw access if he is a member of the owning group.  This algorithm would
> + * produce an empty acl in this case.  We fix this case by modifying
> + * richacl_permission() so that the group mask is always applied to group class
> + * aces.  With this fix, the owner would not have any access (beyond the
> + * implicit permissions always granted to owners).
> + *
> + * NOTE: Depending on the acl and file masks, this algorithm can increase the
> + * number of aces by almost a factor of three in the worst case. This may make
> + * the acl too large for some purposes.
> + */
> +int
> +richacl_apply_masks(struct richacl **acl, kuid_t owner)
> +{
> +	if ((*acl)->a_flags & RICHACL_MASKED) {
> +		struct richacl_alloc alloc = {
> +			.acl = richacl_clone(*acl, GFP_KERNEL),
> +			.count = (*acl)->a_count,
> +		};
> +		if (!alloc.acl)
> +			return -ENOMEM;
> +
> +		if (richacl_move_everyone_aces_down(&alloc) ||
> +		    richacl_propagate_everyone(&alloc) ||
> +		    __richacl_apply_masks(&alloc, owner) ||
> +		    richacl_set_owner_permissions(&alloc) ||
> +		    richacl_set_other_permissions(&alloc) ||
> +		    richacl_isolate_owner_class(&alloc) ||
> +		    richacl_isolate_group_class(&alloc)) {
> +			richacl_put(alloc.acl);
> +			return -ENOMEM;
> +		}
> +
> +		alloc.acl->a_flags &= ~(RICHACL_WRITE_THROUGH | RICHACL_MASKED);
> +		richacl_put(*acl);
> +		*acl = alloc.acl;
> +	}
> +	return 0;
> +}
> +EXPORT_SYMBOL_GPL(richacl_apply_masks);
> diff --git a/include/linux/richacl.h b/include/linux/richacl.h
> index 832b06c..a945f3c 100644
> --- a/include/linux/richacl.h
> +++ b/include/linux/richacl.h
> @@ -332,4 +332,7 @@ extern struct richacl *richacl_inherit(const struct richacl *, int);
>  extern int richacl_permission(struct inode *, const struct richacl *, int);
>  extern struct richacl *richacl_create(struct inode *, struct inode *);
>  
> +/* richacl_compat.c */
> +extern int richacl_apply_masks(struct richacl **, kuid_t);
> +
>  #endif /* __RICHACL_H */
> -- 
> 2.4.3
> 
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