audit: allow audit matching on inode gid

Much like the ability to filter audit on the uid of an inode collected, we
should be able to filter on the gid of the inode.
Signed-off-by: Eric Paris <eparis@redhat.com>

include/linux/audit.h

@@ -224,6 +224,7 @@
 #define AUDIT_DIR	107
 #define AUDIT_FILETYPE	108
 #define AUDIT_OBJ_UID	109
+#define AUDIT_OBJ_GID	110
 
 #define AUDIT_ARG0      200
 #define AUDIT_ARG1      (AUDIT_ARG0+1)

kernel/auditfilter.c

@@ -462,6 +462,7 @@ static struct audit_entry *audit_data_to_entry(struct audit_rule_data *data,
 		case AUDIT_ARG2:
 		case AUDIT_ARG3:
 		case AUDIT_OBJ_UID:
+		case AUDIT_OBJ_GID:
 			break;
 		case AUDIT_ARCH:
 			entry->rule.arch_f = f;

kernel/auditsc.c

@@ -598,6 +598,18 @@ static int audit_filter_rules(struct task_struct *tsk,
 				}
 			}
 			break;
+		case AUDIT_OBJ_GID:
+			if (name) {
+				result = audit_comparator(name->gid, f->op, f->val);
+			} else if (ctx) {
+				list_for_each_entry(n, &ctx->names_list, list) {
+					if (audit_comparator(n->gid, f->op, f->val)) {
+						++result;
+						break;
+					}
+				}
+			}
+			break;
 		case AUDIT_WATCH:
 			if (name)
 				result = audit_watch_compare(rule->watch, name->ino, name->dev);