From: "Frank Filz" Subject: RE: [PATCH v23 08/22] richacl: Compute maximum file masks from an acl Date: Tue, 5 Jul 2016 10:08:37 -0700 Message-ID: <014101d1d6df$e059fd20$a10df760$@mindspring.com> References: <1467294433-3222-1-git-send-email-agruenba@redhat.com> <1467294433-3222-9-git-send-email-agruenba@redhat.com> <1467728537.3800.32.camel@redhat.com> Mime-Version: 1.0 Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: 8BIT Cc: "'Christoph Hellwig'" , "'Theodore Ts'o'" , "'Andreas Dilger'" , "'J. Bruce Fields'" , "'Trond Myklebust'" , "'Anna Schumaker'" , "'Dave Chinner'" , , , , , , , To: "'Jeff Layton'" , "'Andreas Gruenbacher'" , "'Alexander Viro'" Return-path: In-Reply-To: <1467728537.3800.32.camel@redhat.com> Content-Language: en-us Sender: linux-fsdevel-owner@vger.kernel.org List-Id: linux-ext4.vger.kernel.org > > + * Note: functions like richacl_allowed_to_who(), > > +richacl_group_class_allowed(), > > + * and richacl_compute_max_masks() iterate through the entire acl in > > +reverse > > + * order as an optimization. > > + * > > + * In the standard algorithm, aces are considered in forward order. > > +When a > > + * process matches an ace, the permissions in the ace are either > > +allowed or > > + * denied depending on the ace type. Once a permission has been > > +allowed or > > + * denied, it is no longer considered in further aces. > > + * > > + * By iterating through the acl in reverse order, we can compute the > > +same > > + * result without having to keep track of which permissions have been > > +allowed > > + * and denied already. > > + */ > > > > Clever! Hmm, but does that result in examining the whole ACL for most access checks, at least for files where most of the accesses are by the owner, or a member of a specific group (with perhaps a ton of special case users added on the end)? Frank > > + > > +/** > > + * richacl_allowed_to_who - permissions allowed to a specific who > > +value > > + * > > + * Compute the maximum mask values allowed to a specific who value, > > +taking > > + * everyone@ aces 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 of the group > > +class > > + * > > + * Compute the maximum mask values allowed to a process in the group > > +class > > + * (i.e., a process which is not the owner but is in the owning group > > +or > > + * matches a user or group acl entry). This includes permissions > > +granted or > > + * denied by everyone@ aces. > > + * > > + * 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 the acl doesn't contain any group@ aces, > richacl_allowed_to_who() > > + * wasn't called for the owning group. We could make that call now, > but > > + * we already know the result (everyone_allowed). > > + */ > > + 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 > > + * permissions allowed by the acl are disabled. > > + * > > + * We don't make assumptions about who the owner is so that the owner > > +can > > + * change with no effect on the file masks or file mode permission > > +bits; this > > + * means that we must assume that all entries can match the owner. > > + */ > > +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 of 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, and the group class > cannot > > + * have fewer permissions than the other class. > > + */ > > + > > +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_WRITE_THROUGH | RICHACL_MASKED); } > > +EXPORT_SYMBOL_GPL(richacl_compute_max_masks); > > diff --git a/include/linux/richacl.h b/include/linux/richacl.h index > > 9102ef0..3559b2c 100644 > > --- a/include/linux/richacl.h > > +++ b/include/linux/richacl.h > > @@ -178,5 +178,6 @@ extern void richace_copy(struct richace *, const > > struct richace *); > > extern int richacl_masks_to_mode(const struct richacl *); > > 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 *); > > > > #endif /* __RICHACL_H */ > > Reviewed-by: Jeff Layton > -- > To unsubscribe from this list: send the line "unsubscribe linux-fsdevel" in the > body of a message to majordomo@vger.kernel.org More majordomo info at > http://vger.kernel.org/majordomo-info.html --- This email has been checked for viruses by Avast antivirus software. https://www.avast.com/antivirus