From: Deepa Dinamani Subject: Re: Y2038 bug in ext4 recently_deleted() function Date: Thu, 17 Aug 2017 18:23:26 -0700 Message-ID: References: <20170808050517.7160-1-wshilong@ddn.com> <20170816164211.GA31117@quack2.suse.cz> <3ED34739A4E85E4F894367D57617CDEFEDA401CE@LAX-EX-MB2.datadirect.datadirectnet.com> <20170817091959.GB7644@quack2.suse.cz> <20170817092153.GA14074@quack2.suse.cz> Mime-Version: 1.0 Content-Type: text/plain; charset="UTF-8" Cc: "Theodore Ts'o" , Arnd Bergmann , Wang Shilong , Wang Shilong , "linux-ext4@vger.kernel.org" , Shuichi Ihara , Li Xi , Jan Kara To: Andreas Dilger Return-path: Received: from mail-io0-f178.google.com ([209.85.223.178]:38625 "EHLO mail-io0-f178.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753345AbdHRBX1 (ORCPT ); Thu, 17 Aug 2017 21:23:27 -0400 Received: by mail-io0-f178.google.com with SMTP id g71so28676126ioe.5 for ; Thu, 17 Aug 2017 18:23:27 -0700 (PDT) In-Reply-To: Sender: linux-ext4-owner@vger.kernel.org List-ID: > Strange, I never even knew recently_deleted() existed, even though it was > added to the tree 4 years ago yesterday. It looks like this is only used > with the no-journal code, which I don't really interact with. > > One thing I did notice when looking at it is that there is a Y2038 bug in > recently_deleted(), as it is comparing 32-bit i_dtime directly with 64-bit > get_seconds(). I don't think dtime has widened on the disk layout for ext4 according to https://ext4.wiki.kernel.org/index.php/Ext4_Disk_Layout. So I am not sure how fixing the internal implementation would be useful until we do that. Is there a plan for that? As far as get_seconds() is concerned, get_seconds() returns unsigned long which is 64 bits on a 64 bit arch and 32 bit on a 32 bit arch. Since dtime variable is declared as unsigned long in this function, same holds for the size of this variable. There is no y2038 problem on a 64 bit machine. So moving to the case of a 32 bit machine: get_seconds() can return values until year 2106. And, recentcy at max can only be 35. Analyzing the current line: if (dtime && (dtime < now) && (now < dtime + recentcy)) The above equation should work fine at least until 35 seconds before y2038 deadline. -Deepa