audit: allow matching on obj_uid

Allow syscall exit filter matching based on the uid of the owner of an
inode used in a syscall.  aka:

auditctl -a always,exit -S open -F obj_uid=0 -F perm=wa
Signed-off-by: NEric Paris <eparis@redhat.com>

include/linux/audit.h

@@ -223,6 +223,7 @@
 #define AUDIT_PERM	106
 #define AUDIT_DIR	107
 #define AUDIT_FILETYPE	108
+#define AUDIT_OBJ_UID	109
 
 #define AUDIT_ARG0      200
 #define AUDIT_ARG1      (AUDIT_ARG0+1)

kernel/auditfilter.c

@@ -461,6 +461,7 @@ static struct audit_entry *audit_data_to_entry(struct audit_rule_data *data,
 		case AUDIT_ARG1:
 		case AUDIT_ARG2:
 		case AUDIT_ARG3:
+		case AUDIT_OBJ_UID:
 			break;
 		case AUDIT_ARCH:
 			entry->rule.arch_f = f;

kernel/auditsc.c

@@ -586,6 +586,18 @@ static int audit_filter_rules(struct task_struct *tsk,
 				}
 			}
 			break;
+		case AUDIT_OBJ_UID:
+			if (name) {
+				result = audit_comparator(name->uid, f->op, f->val);
+			} else if (ctx) {
+				list_for_each_entry(n, &ctx->names_list, list) {
+					if (audit_comparator(n->uid, f->op, f->val)) {
+						++result;
+						break;
+					}
+				}
+			}
+			break;
 		case AUDIT_WATCH:
 			if (name)
 				result = audit_watch_compare(rule->watch, name->ino, name->dev);