From: Jeff Layton Subject: Re: [PATCH v23 08/22] richacl: Compute maximum file masks from an acl Date: Tue, 05 Jul 2016 10:22:17 -0400 Message-ID: <1467728537.3800.32.camel@redhat.com> References: <1467294433-3222-1-git-send-email-agruenba@redhat.com> <1467294433-3222-9-git-send-email-agruenba@redhat.com> Mime-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: QUOTED-PRINTABLE Cc: Christoph Hellwig , Theodore Ts'o , Andreas Dilger , "J. Bruce Fields" , Trond Myklebust , Anna Schumaker , Dave Chinner , linux-ext4-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, xfs-VZNHf3L845pBDgjK7y7TUQ@public.gmane.org, linux-kernel-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, linux-fsdevel-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, linux-nfs-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, linux-cifs-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, linux-api-u79uwXL29TY76Z2rM5mHXA@public.gmane.org To: Andreas Gruenbacher , Alexander Viro Return-path: In-Reply-To: <1467294433-3222-9-git-send-email-agruenba-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org> Sender: linux-nfs-owner-u79uwXL29TY76Z2rM5mHXA@public.gmane.org List-Id: linux-ext4.vger.kernel.org On Thu, 2016-06-30 at 15:46 +0200, Andreas Gruenbacher wrote: > Compute upper bound owner, group, and other file masks with as few > permissions as possible without denying any permissions that the NFSv= 4 > acl in a richacl grants. >=20 > 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 provide file masks > (such as setting an acl via nfsd).=C2=A0=C2=A0When user-space sets an= acl via > setxattr, the extended attribute already includes the file masks. >=20 > Setting an acl also sets the file mode permission bits: they are > determined by the file masks; see richacl_masks_to_mode(). >=20 > Signed-off-by: Andreas Gruenbacher > Reviewed-by: J. Bruce Fields > --- > =C2=A0fs/richacl.c=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2= =A0=C2=A0=C2=A0=C2=A0| 157 ++++++++++++++++++++++++++++++++++++++++++++= ++++ > =C2=A0include/linux/richacl.h |=C2=A0=C2=A0=C2=A01 + > =C2=A02 files changed, 158 insertions(+) >=20 > diff --git a/fs/richacl.c b/fs/richacl.c > index d0a4135..056228f 100644 > --- a/fs/richacl.c > +++ b/fs/richacl.c > @@ -181,3 +181,160 @@ richacl_want_to_mask(unsigned int want) > =C2=A0 return mask; > =C2=A0} > =C2=A0EXPORT_SYMBOL_GPL(richacl_want_to_mask); > + > +/* > + * Note: functions like richacl_allowed_to_who(), richacl_group_clas= s_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.=C2= =A0=C2=A0When a > + * process matches an ace, the permissions in the ace are either all= owed or > + * denied depending on the ace type.=C2=A0=C2=A0Once a permission ha= s 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 bee= n allowed > + * and denied already. > + */ >=20 Clever! > + > +/** > + * richacl_allowed_to_who=C2=A0=C2=A0-=C2=A0=C2=A0permissions allowe= d 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, > + =C2=A0=C2=A0=C2=A0struct richace *who) > +{ > + struct richace *ace; > + unsigned int allowed =3D 0; > + > + richacl_for_each_entry_reverse(ace, acl) { > + if (richace_is_inherit_only(ace)) > + continue; > + if (richace_is_same_identifier(ace, who) || > + =C2=A0=C2=A0=C2=A0=C2=A0richace_is_everyone(ace)) { > + if (richace_is_allow(ace)) > + allowed |=3D ace->e_mask; > + else if (richace_is_deny(ace)) > + allowed &=3D ~ace->e_mask; > + } > + } > + return allowed; > +} > + > +/** > + * richacl_group_class_allowed=C2=A0=C2=A0-=C2=A0=C2=A0maximum permi= ssions 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 grou= p or > + * matches a user or group acl entry).=C2=A0=C2=A0This includes perm= issions 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 =3D 0, group_class_allowed =3D 0; > + int had_group_ace =3D 0; > + > + richacl_for_each_entry_reverse(ace, acl) { > + if (richace_is_inherit_only(ace) || > + =C2=A0=C2=A0=C2=A0=C2=A0richace_is_owner(ace)) > + continue; > + > + if (richace_is_everyone(ace)) { > + if (richace_is_allow(ace)) > + everyone_allowed |=3D ace->e_mask; > + else if (richace_is_deny(ace)) > + everyone_allowed &=3D ~ace->e_mask; > + } else { > + group_class_allowed |=3D > + richacl_allowed_to_who(acl, ace); > + > + if (richace_is_group(ace)) > + had_group_ace =3D 1; > + } > + } > + /* > + =C2=A0* If the acl doesn't contain any group@ aces, richacl_allowed= _to_who() > + =C2=A0* wasn't called for the owning group.=C2=A0=C2=A0We could mak= e that call now, but > + =C2=A0* we already know the result (everyone_allowed). > + =C2=A0*/ > + if (!had_group_ace) > + group_class_allowed |=3D everyone_allowed; > + return group_class_allowed; > +} > + > +/** > + * richacl_compute_max_masks=C2=A0=C2=A0-=C2=A0=C2=A0compute upper b= ound masks > + * > + * Computes upper bound owner, group, and other masks so that none o= f the > + * permissions allowed by the acl are disabled. > + * > + * We don't make assumptions about who the owner is so that the owne= r can > + * change with no effect on the file masks or file mode permission b= its; this > + * means that we must assume that all entries can match the owner. > + */ > +void richacl_compute_max_masks(struct richacl *acl) > +{ > + unsigned int gmask =3D ~0; > + struct richace *ace; > + > + /* > + =C2=A0* @gmask contains all permissions which the group class is ev= er > + =C2=A0* allowed.=C2=A0=C2=A0We use it to avoid adding permissions t= o the group mask > + =C2=A0* from everyone@ allow aces which the group class is always d= enied > + =C2=A0* through other aces.=C2=A0=C2=A0For example, the following a= cl would otherwise > + =C2=A0* result in a group mask of rw: > + =C2=A0* > + =C2=A0* group@:w::deny > + =C2=A0* everyone@:rw::allow > + =C2=A0* > + =C2=A0* Avoid computing @gmask for acls which do not include any gr= oup class > + =C2=A0* deny aces: in such acls, the group class is never denied an= y > + =C2=A0* permissions from everyone@ allow aces, and the group class = cannot > + =C2=A0* have fewer permissions than the other class. > + =C2=A0*/ > + > +restart: > + acl->a_owner_mask =3D 0; > + acl->a_group_mask =3D 0; > + acl->a_other_mask =3D 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 |=3D ace->e_mask; > + else if (richace_is_deny(ace)) > + acl->a_owner_mask &=3D ~ace->e_mask; > + } else if (richace_is_everyone(ace)) { > + if (richace_is_allow(ace)) { > + acl->a_owner_mask |=3D ace->e_mask; > + acl->a_group_mask |=3D ace->e_mask & gmask; > + acl->a_other_mask |=3D ace->e_mask; > + } else if (richace_is_deny(ace)) { > + acl->a_owner_mask &=3D ~ace->e_mask; > + acl->a_group_mask &=3D ~ace->e_mask; > + acl->a_other_mask &=3D ~ace->e_mask; > + } > + } else { > + if (richace_is_allow(ace)) { > + acl->a_owner_mask |=3D ace->e_mask & gmask; > + acl->a_group_mask |=3D ace->e_mask & gmask; > + } else if (richace_is_deny(ace) && gmask =3D=3D ~0) { > + gmask =3D richacl_group_class_allowed(acl); > + if (likely(gmask !=3D ~0)) > + /* should always be true */ > + goto restart; > + } > + } > + } > + > + acl->a_flags &=3D ~(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 *); > =C2=A0extern int richacl_masks_to_mode(const struct richacl *); > =C2=A0extern unsigned int richacl_mode_to_mask(umode_t); > =C2=A0extern unsigned int richacl_want_to_mask(unsigned int); > +extern void richacl_compute_max_masks(struct richacl *); > =C2=A0 > =C2=A0#endif /* __RICHACL_H */ Reviewed-by: Jeff Layton -- To unsubscribe from this list: send the line "unsubscribe linux-nfs" in the body of a message to majordomo-u79uwXL29TY76Z2rM5mHXA@public.gmane.org More majordomo info at http://vger.kernel.org/majordomo-info.html