From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 0FEEBC433EF for ; Sat, 23 Oct 2021 22:48:34 +0000 (UTC) Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by mail.kernel.org (Postfix) with ESMTP id 7230460F46 for ; Sat, 23 Oct 2021 22:48:33 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.4.1 mail.kernel.org 7230460F46 Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=infradead.org Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=kvack.org Received: by kanga.kvack.org (Postfix) id AB076940007; Sat, 23 Oct 2021 18:48:32 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id A5F596B0071; Sat, 23 Oct 2021 18:48:32 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 92734940007; Sat, 23 Oct 2021 18:48:32 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from forelay.hostedemail.com (smtprelay0059.hostedemail.com [216.40.44.59]) by kanga.kvack.org (Postfix) with ESMTP id 8012A6B006C for ; Sat, 23 Oct 2021 18:48:32 -0400 (EDT) Received: from smtpin09.hostedemail.com (10.5.19.251.rfc1918.com [10.5.19.251]) by forelay05.hostedemail.com (Postfix) with ESMTP id 281591802EAB5 for ; Sat, 23 Oct 2021 22:48:32 +0000 (UTC) X-FDA: 78729192864.09.5B1261E Received: from casper.infradead.org (casper.infradead.org [90.155.50.34]) by imf25.hostedemail.com (Postfix) with ESMTP id 41C0FB000188 for ; Sat, 23 Oct 2021 22:48:26 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=infradead.org; s=casper.20170209; h=In-Reply-To:Content-Type:MIME-Version: References:Message-ID:Subject:Cc:To:From:Date:Sender:Reply-To: Content-Transfer-Encoding:Content-ID:Content-Description; bh=9g2tErlL7LnzYe+gFuxTumzb45DnMU0NhCfOnwA3Slc=; b=lO6yHMl6zQkM3Zj6Tte5iNdIeV 2BES/2v62RD46zUZdp/q5yqCFfZnsUV/G/P0o97mb4iAM9AJd+6uG51oid+uVn1QfZUbsMkqKlGBz qY+22oE5gOewr0QZItqF3mZzTBfWG8bLnO5o/YvOdjGkWa/BjcV+KF96I246yhkJBmKPwHmEJzUtA HZ+SgUQVTubzCoJFUmE9axY/dtnwyyYAqm6Oe6Kg6djGod1M8DRvNbK8adSQMBYKZwsCQ+AJ2Rm1A MXN2Qv0G5gs7TtgHr8lilq11jmy90P1iOUf64QtX87H6CzupyfLel8DNNwF0aJR8WFl247fbqT2wl htxgl3NQ==; Received: from willy by casper.infradead.org with local (Exim 4.94.2 #2 (Red Hat Linux)) id 1mePmM-00EwBX-8P; Sat, 23 Oct 2021 22:46:41 +0000 Date: Sat, 23 Oct 2021 23:46:18 +0100 From: Matthew Wilcox To: Kees Cook Cc: Mike Rapoport , Dmitry Vyukov , syzbot , Jordy Zomer , akpm@linux-foundation.org, linux-kernel@vger.kernel.org, linux-mm@kvack.org, syzkaller-bugs@googlegroups.com Subject: Re: [syzbot] WARNING: refcount bug in sys_memfd_secret Message-ID: References: <00000000000062d0fc05cef24c57@google.com> <088FF23B-CD8E-4E53-B702-53E2C2382062@chromium.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <088FF23B-CD8E-4E53-B702-53E2C2382062@chromium.org> X-Stat-Signature: wy683azhs97sxchntmqifo693u6x9wzw X-Rspamd-Server: rspam01 X-Rspamd-Queue-Id: 41C0FB000188 Authentication-Results: imf25.hostedemail.com; dkim=pass header.d=infradead.org header.s=casper.20170209 header.b=lO6yHMl6; dmarc=none; spf=none (imf25.hostedemail.com: domain of willy@infradead.org has no SPF policy when checking 90.155.50.34) smtp.mailfrom=willy@infradead.org X-HE-Tag: 1635029306-204147 X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: On Sat, Oct 23, 2021 at 10:03:11AM -0700, Kees Cook wrote: > On October 23, 2021 8:27:28 AM PDT, Mike Rapoport wrote: > >and my first reaction was to send a revert the untested commit 110860541f44 > >("mm/secretmem: use refcount_t instead of atomic_t"). I think you should. This isn't a real problem. And it abuses the refcount_t interface. Your hack is clever, but it's fundamentally wrong.