audit: unswing cap_* fields in PATH records

The cap_* fields swing in and out of PATH records.
If no capabilities are set, the cap_* fields are completely missing and when
one of the cap_fi or cap_fp values is empty, that field is omitted.

Original:
type=PATH msg=audit(04/20/2017 12:17:11.222:193) : item=1 name=/lib64/ld-linux-x86-64.so.2 inode=787694 dev=08:03 mode=file,755 ouid=root ogid=root rdev=00:00 obj=system_u:object_r:ld_so_t:s0 nametype=NORMAL
type=PATH msg=audit(04/20/2017 12:17:11.222:193) : item=0 name=/home/sleep inode=1319469 dev=08:03 mode=file,suid,755 ouid=root ogid=root rdev=00:00 obj=system_u:object_r:bin_t:s0 nametype=NORMAL cap_fp=sys_admin cap_fe=1 cap_fver=2

Normalize the PATH record by always printing all 4 cap_* fields.

Fixed:
type=PATH msg=audit(04/20/2017 13:01:31.679:201) : item=1 name=/lib64/ld-linux-x86-64.so.2 inode=787694 dev=08:03 mode=file,755 ouid=root ogid=root rdev=00:00 obj=system_u:object_r:ld_so_t:s0 nametype=NORMAL cap_fp=none cap_fi=none cap_fe=0 cap_fver=0
type=PATH msg=audit(04/20/2017 13:01:31.679:201) : item=0 name=/home/sleep inode=1319469 dev=08:03 mode=file,suid,755 ouid=root ogid=root rdev=00:00 obj=system_u:object_r:bin_t:s0 nametype=NORMAL cap_fp=sys_admin cap_fi=none cap_fe=1 cap_fver=2

See: https://github.com/linux-audit/audit-kernel/issues/42

Signed-off-by: Richard Guy Briggs <rgb@redhat.com>
Signed-off-by: Paul Moore <paul@paul-moore.com>

kernel/audit.c

@@ -1999,22 +1999,10 @@ void audit_log_cap(struct audit_buffer *ab, char *prefix, kernel_cap_t *cap)
 
 static void audit_log_fcaps(struct audit_buffer *ab, struct audit_names *name)
 {
-	kernel_cap_t *perm = &name->fcap.permitted;
-	kernel_cap_t *inh = &name->fcap.inheritable;
-	int log = 0;
-
-	if (!cap_isclear(*perm)) {
-		audit_log_cap(ab, "cap_fp", perm);
-		log = 1;
-	}
-	if (!cap_isclear(*inh)) {
-		audit_log_cap(ab, "cap_fi", inh);
-		log = 1;
-	}
-
-	if (log)
-		audit_log_format(ab, " cap_fe=%d cap_fver=%x",
-				 name->fcap.fE, name->fcap_ver);
+	audit_log_cap(ab, "cap_fp", &name->fcap.permitted);
+	audit_log_cap(ab, "cap_fi", &name->fcap.inheritable);
+	audit_log_format(ab, " cap_fe=%d cap_fver=%x",
+			 name->fcap.fE, name->fcap_ver);
 }
 
 static inline int audit_copy_fcaps(struct audit_names *name,