Return-Path: Received: from fieldses.org ([173.255.197.46]:38349 "EHLO fieldses.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751807AbbDTV2L (ORCPT ); Mon, 20 Apr 2015 17:28:11 -0400 Date: Mon, 20 Apr 2015 17:28:10 -0400 To: Andreas Gruenbacher Cc: linux-kernel@vger.kernel.org, linux-fsdevel@vger.kernel.org, linux-nfs@vger.kernel.org Subject: Re: [RFC 11/39] richacl: Compute maximum file masks from an acl Message-ID: <20150420212810.GB27895@fieldses.org> References: <75f97eb880b1bbb47b0aa146d3f528e32de06744.1427471526.git.agruenba@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii In-Reply-To: <75f97eb880b1bbb47b0aa146d3f528e32de06744.1427471526.git.agruenba@redhat.com> From: bfields@fieldses.org (J. Bruce Fields) Sender: linux-nfs-owner@vger.kernel.org List-ID: On Fri, Mar 27, 2015 at 05:50:09PM +0100, Andreas Gruenbacher wrote: > Compute upper bound owner, group, and other file masks with as few > permissions as possible without denying any permissions that the NFSv4 > acl in a richacl grants. > > This algorithm is used when a file inherits an acl at create time and > when an acl is set via a mechanism that does not specify file modes > (such as via nfsd). When user-space sets an acl, the file masks are > passed in as part of the xattr. > > When setting a richacl, the file masks determine what the file > permission bits will be set to; see richacl_masks_to_mode(). > > Signed-off-by: Andreas Gruenbacher > --- > fs/richacl_base.c | 128 ++++++++++++++++++++++++++++++++++++++++++++++++ > include/linux/richacl.h | 1 + > 2 files changed, 129 insertions(+) > > diff --git a/fs/richacl_base.c b/fs/richacl_base.c > index 9cd15ca..d9e557a 100644 > --- a/fs/richacl_base.c > +++ b/fs/richacl_base.c > @@ -173,3 +173,131 @@ richacl_want_to_mask(unsigned int want) > return mask; > } > EXPORT_SYMBOL_GPL(richacl_want_to_mask); > + > +/** > + * richacl_allowed_to_who - mask flags allowed to a specific who value > + * > + * Computes the mask values allowed to a specific who value, taking > + * EVERYONE@ entries into account. > + */ > +static unsigned int richacl_allowed_to_who(struct richacl *acl, > + struct richace *who) > +{ > + struct richace *ace; > + unsigned int allowed = 0; > + > + richacl_for_each_entry_reverse(ace, acl) { > + if (richace_is_inherit_only(ace)) > + continue; > + if (richace_is_same_identifier(ace, who) || > + richace_is_everyone(ace)) { > + if (richace_is_allow(ace)) > + allowed |= ace->e_mask; > + else if (richace_is_deny(ace)) > + allowed &= ~ace->e_mask; > + } > + } > + return allowed; > +} > + > +/** > + * richacl_group_class_allowed - maximum permissions the group class is allowed > + * > + * See richacl_compute_max_masks(). > + */ > +static unsigned int richacl_group_class_allowed(struct richacl *acl) > +{ > + struct richace *ace; > + unsigned int everyone_allowed = 0, group_class_allowed = 0; > + int had_group_ace = 0; > + > + richacl_for_each_entry_reverse(ace, acl) { > + if (richace_is_inherit_only(ace) || > + richace_is_owner(ace)) > + continue; > + > + if (richace_is_everyone(ace)) { > + if (richace_is_allow(ace)) > + everyone_allowed |= ace->e_mask; > + else if (richace_is_deny(ace)) > + everyone_allowed &= ~ace->e_mask; > + } else { > + group_class_allowed |= > + richacl_allowed_to_who(acl, ace); > + > + if (richace_is_group(ace)) > + had_group_ace = 1; > + } > + } > + if (!had_group_ace) > + group_class_allowed |= everyone_allowed; > + return group_class_allowed; > +} > + > +/** > + * richacl_compute_max_masks - compute upper bound masks > + * > + * Computes upper bound owner, group, and other masks so that none of > + * the mask flags allowed by the acl are disabled (for any choice of the > + * file owner or group membership). > + */ > +void richacl_compute_max_masks(struct richacl *acl) > +{ > + unsigned int gmask = ~0; > + struct richace *ace; > + > + /* > + * @gmask contains all permissions which the group class is ever > + * allowed. We use it to avoid adding permissions to the group mask > + * from everyone@ allow aces which the group class is always denied > + * through other aces. For example, the following acl would otherwise > + * result in a group mask or rw: > + * > + * group@:w::deny > + * everyone@:rw::allow > + * > + * Avoid computing @gmask for acls which do not include any group class > + * deny aces: in such acls, the group class is never denied any > + * permissions from everyone@ allow aces. > + */ Cripes, by the time I got to this point I'd already written one response where I complained this was wrong, another where I explained why it was right, and gone back and forth a couple more times. Feel free to add a Reviewed-by: J. Bruce Fields but maybe we could use a couple more examples here. Or a paper. --b. > + > +restart: > + acl->a_owner_mask = 0; > + acl->a_group_mask = 0; > + acl->a_other_mask = 0; > + > + richacl_for_each_entry_reverse(ace, acl) { > + if (richace_is_inherit_only(ace)) > + continue; > + > + if (richace_is_owner(ace)) { > + if (richace_is_allow(ace)) > + acl->a_owner_mask |= ace->e_mask; > + else if (richace_is_deny(ace)) > + acl->a_owner_mask &= ~ace->e_mask; > + } else if (richace_is_everyone(ace)) { > + if (richace_is_allow(ace)) { > + acl->a_owner_mask |= ace->e_mask; > + acl->a_group_mask |= ace->e_mask & gmask; > + acl->a_other_mask |= ace->e_mask; > + } else if (richace_is_deny(ace)) { > + acl->a_owner_mask &= ~ace->e_mask; > + acl->a_group_mask &= ~ace->e_mask; > + acl->a_other_mask &= ~ace->e_mask; > + } > + } else { > + if (richace_is_allow(ace)) { > + acl->a_owner_mask |= ace->e_mask & gmask; > + acl->a_group_mask |= ace->e_mask & gmask; > + } else if (richace_is_deny(ace) && gmask == ~0) { > + gmask = richacl_group_class_allowed(acl); > + if (likely(gmask != ~0)) > + /* should always be true */ > + goto restart; > + } > + } > + } > + > + acl->a_flags &= ~RICHACL_MASKED; > +} > +EXPORT_SYMBOL_GPL(richacl_compute_max_masks); > diff --git a/include/linux/richacl.h b/include/linux/richacl.h > index 2120aa6..25f45f7 100644 > --- a/include/linux/richacl.h > +++ b/include/linux/richacl.h > @@ -288,5 +288,6 @@ extern struct richacl *richacl_alloc(int, gfp_t); > extern int richacl_masks_to_mode(const struct richacl *); > extern unsigned int richacl_mode_to_mask(mode_t); > extern unsigned int richacl_want_to_mask(unsigned int); > +extern void richacl_compute_max_masks(struct richacl *); > > #endif /* __RICHACL_H */ > -- > 2.1.0 > > -- > To unsubscribe from this list: send the line "unsubscribe linux-nfs" in > the body of a message to majordomo@vger.kernel.org > More majordomo info at http://vger.kernel.org/majordomo-info.html