audit: allow not equal op for audit by executable

BugLink: https://bugs.launchpad.net/bugs/1791953

[ Upstream commit 23bcc480 ]

Current implementation of auditing by executable name only implements
the 'equal' operator. This patch extends it to also support the 'not
equal' operator.

See: https://github.com/linux-audit/audit-kernel/issues/53Signed-off-by: Ondrej Mosnacek <omosnace@redhat.com>
Reviewed-by: Richard Guy Briggs <rgb@redhat.com>
Signed-off-by: Paul Moore <paul@paul-moore.com>
Signed-off-by: Sasha Levin <alexander.levin@microsoft.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Stefan Bader <stefan.bader@canonical.com>
Signed-off-by: Kleber Sacilotto de Souza <kleber.souza@canonical.com>

kernel/auditfilter.c

@@ -406,7 +406,7 @@ static int audit_field_valid(struct audit_entry *entry, struct audit_field *f)
 			return -EINVAL;
 		break;
 	case AUDIT_EXE:
-		if (f->op != Audit_equal)
+		if (f->op != Audit_not_equal && f->op != Audit_equal)
 			return -EINVAL;
 		if (entry->rule.listnr != AUDIT_FILTER_EXIT)
 			return -EINVAL;

kernel/auditsc.c

@@ -470,6 +470,8 @@ static int audit_filter_rules(struct task_struct *tsk,
 			break;
 		case AUDIT_EXE:
 			result = audit_exe_compare(tsk, rule->exe);
+			if (f->op == Audit_not_equal)
+				result = !result;
 			break;
 		case AUDIT_UID:
 			result = audit_uid_comparator(cred->uid, f->op, f->uid);