From: Andreas Gruenbacher <agruenba@xxxxxxxxxx> 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 provide file masks (such as setting an acl via nfsd). When user-space sets an acl via setxattr, the extended attribute already includes the file masks. Setting an acl also sets the file mode permission bits: they are determined by the file masks; see richacl_masks_to_mode(). Signed-off-by: Andreas Gruenbacher <agruenba@xxxxxxxxxx> Reviewed-by: J. Bruce Fields <bfields@xxxxxxxxxx> --- fs/richacl_base.c | 156 ++++++++++++++++++++++++++++++++++++++++++++++++ include/linux/richacl.h | 1 + 2 files changed, 157 insertions(+) diff --git a/fs/richacl_base.c b/fs/richacl_base.c index d12f984..23e9824 100644 --- a/fs/richacl_base.c +++ b/fs/richacl_base.c @@ -178,3 +178,159 @@ richacl_want_to_mask(unsigned int want) return mask; } EXPORT_SYMBOL_GPL(richacl_want_to_mask); + +/* + * 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. + */ + +/** + * 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 the group class is allowed + * + * 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 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, kuid_t owner) +{ + 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) || + (richace_is_unix_user(ace) && + uid_eq(ace->e_id.uid, owner))) { + 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 1ae0bf8..90baca3 100644 --- a/include/linux/richacl.h +++ b/include/linux/richacl.h @@ -301,5 +301,6 @@ 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(mode_t); extern unsigned int richacl_want_to_mask(unsigned int); +extern void richacl_compute_max_masks(struct richacl *, kuid_t); #endif /* __RICHACL_H */ -- 2.4.3 -- To unsubscribe from this list: send the line "unsubscribe linux-api" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html