audit: allow interfield comparison between gid and ogid

Allow audit rules to compare the gid of the running task to the gid of the
inode in question.

Signed-off-by: Eric Paris <[e-mail]>

include/linux/audit.h

···
 
 /* AUDIT_FIELD_COMPARE rule list */
 #define AUDIT_COMPARE_UID_TO_OBJ_UID	1
+#define AUDIT_COMPARE_GID_TO_OBJ_GID	2
 
-#define AUDIT_MAX_FIELD_COMPARE	AUDIT_COMPARE_UID_TO_OBJ_UID
+#define AUDIT_MAX_FIELD_COMPARE	AUDIT_COMPARE_GID_TO_OBJ_GID
 /* Rule fields */
 				/* These are useful when checking the
 				 * task structure at task creation time

kernel/auditsc.c

···
 	uid_t uid2;
 	int rc;
 
+	BUILD_BUG_ON(sizeof(uid_t) != sizeof(gid_t));
+
 	if (name) {
 		addr = (unsigned long)name;
 		addr += name_offset;
···
 	case AUDIT_COMPARE_UID_TO_OBJ_UID:
 		return audit_compare_id(cred->uid,
 					name, offsetof(struct audit_names, uid),
+					f, ctx);
+	case AUDIT_COMPARE_GID_TO_OBJ_GID:
+		return audit_compare_id(cred->gid,
+					name, offsetof(struct audit_names, gid),
 					f, ctx);
 	default:
 		WARN(1, "Missing AUDIT_COMPARE define.  Report as a bug\n");