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: Richard Guy Briggs <rgb@redhat.com>
Reviewed-by: Serge Hallyn <serge@hallyn.com>
Acked-by: James Morris <james.l.morris@oracle.com>
Acked-by: Kees Cook <keescook@chromium.org>
Okay-ished-by: Paul Moore <paul@paul-moore.com>
Signed-off-by: James Morris <james.l.morris@oracle.com>

diff --git a/security/commoncap.c b/security/commoncap.c
index be9bca5..4c9af6e 100644 (file)
--- a/security/commoncap.c
+++ b/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;
        }