capabilities: intuitive names for cap gain status

Introduce macros cap_gained, cap_grew, cap_full to make the use of the
negation of is_subset() easier to read and analyse.
Signed-off-by: NRichard Guy Briggs <rgb@redhat.com>
Reviewed-by: NSerge Hallyn <serge@hallyn.com>
Acked-by: NJames Morris <james.l.morris@oracle.com>
Acked-by: NKees Cook <keescook@chromium.org>
Okay-ished-by: NPaul Moore <paul@paul-moore.com>
Signed-off-by: NJames Morris <james.l.morris@oracle.com>

security/commoncap.c

@@ -741,6 +741,12 @@ static void handle_privileged_root(struct linux_binprm *bprm, bool has_cap,
 		*effective = true;
 }
 
+#define __cap_gained(field, target, source) \
+	!cap_issubset(target->cap_##field, source->cap_##field)
+#define __cap_grew(target, source, cred) \
+	!cap_issubset(cred->cap_##target, cred->cap_##source)
+#define __cap_full(field, cred) \
+	cap_issubset(CAP_FULL_SET, cred->cap_##field)
 /**
  * cap_bprm_set_creds - Set up the proposed credentials for execve().
  * @bprm: The execution parameters, including the proposed creds
@@ -769,10 +775,9 @@ int cap_bprm_set_creds(struct linux_binprm *bprm)
 	handle_privileged_root(bprm, has_cap, &effective, root_uid);
 
 	/* if we have fs caps, clear dangerous personality flags */
-	if (!cap_issubset(new->cap_permitted, old->cap_permitted))
+	if (__cap_gained(permitted, new, old))
 		bprm->per_clear |= PER_CLEAR_ON_SETID;
 
-
 	/* Don't let someone trace a set[ug]id/setpcap binary with the revised
 	 * credentials unless they have the appropriate permit.
 	 *
@@ -780,8 +785,7 @@ int cap_bprm_set_creds(struct linux_binprm *bprm)
 	 */
 	is_setid = !uid_eq(new->euid, old->uid) || !gid_eq(new->egid, old->gid);
 
-	if ((is_setid ||
-	     !cap_issubset(new->cap_permitted, old->cap_permitted)) &&
+	if ((is_setid || __cap_gained(permitted, new, old)) &&
 	    ((bprm->unsafe & ~LSM_UNSAFE_PTRACE) ||
 	     !ptracer_capable(current, new->user_ns))) {
 		/* downgrade; they get no more than they had, and maybe less */
@@ -831,8 +835,8 @@ int cap_bprm_set_creds(struct linux_binprm *bprm)
 	 * Number 1 above might fail if you don't have a full bset, but I think
 	 * that is interesting information to audit.
 	 */
-	if (!cap_issubset(new->cap_effective, new->cap_ambient)) {
-		if (!cap_issubset(CAP_FULL_SET, new->cap_effective) ||
+	if (__cap_grew(effective, ambient, new)) {
+		if (!__cap_full(effective, new) ||
 		    !uid_eq(new->euid, root_uid) || !uid_eq(new->uid, root_uid) ||
 		    issecure(SECURE_NOROOT)) {
 			ret = audit_log_bprm_fcaps(bprm, new, old);
@@ -852,7 +856,7 @@ int cap_bprm_set_creds(struct linux_binprm *bprm)
 		bprm->cap_elevated = 1;
 	} else if (!uid_eq(new->uid, root_uid)) {
 		if (effective ||
-		    !cap_issubset(new->cap_permitted, new->cap_ambient))
+		    __cap_grew(permitted, ambient, new))
 			bprm->cap_elevated = 1;
 	}