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 X-Spam-Level: X-Spam-Status: No, score=-3.8 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS autolearn=no autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id B68ACC433E1 for ; Tue, 18 Aug 2020 15:17:45 +0000 (UTC) Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by mail.kernel.org (Postfix) with ESMTP id 27A6C2076E for ; Tue, 18 Aug 2020 15:17:45 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 27A6C2076E Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=zeniv.linux.org.uk Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=owner-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix) id 9465D8D0016; Tue, 18 Aug 2020 11:17:44 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id 8CF198D0003; Tue, 18 Aug 2020 11:17:44 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 7BE1A8D0016; Tue, 18 Aug 2020 11:17:44 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from forelay.hostedemail.com (smtprelay0031.hostedemail.com [216.40.44.31]) by kanga.kvack.org (Postfix) with ESMTP id 600198D0003 for ; Tue, 18 Aug 2020 11:17:44 -0400 (EDT) Received: from smtpin07.hostedemail.com (10.5.19.251.rfc1918.com [10.5.19.251]) by forelay05.hostedemail.com (Postfix) with ESMTP id 0DA13181AEF21 for ; Tue, 18 Aug 2020 15:17:44 +0000 (UTC) X-FDA: 77164044048.07.curve67_3e0487c27020 Received: from filter.hostedemail.com (10.5.16.251.rfc1918.com [10.5.16.251]) by smtpin07.hostedemail.com (Postfix) with ESMTP id BF1C81803F780 for ; Tue, 18 Aug 2020 15:17:24 +0000 (UTC) X-HE-Tag: curve67_3e0487c27020 X-Filterd-Recvd-Size: 1888 Received: from ZenIV.linux.org.uk (zeniv.linux.org.uk [195.92.253.2]) by imf20.hostedemail.com (Postfix) with ESMTP for ; Tue, 18 Aug 2020 15:17:24 +0000 (UTC) Received: from viro by ZenIV.linux.org.uk with local (Exim 4.92.3 #3 (Red Hat Linux)) id 1k83MJ-000Ma4-5q; Tue, 18 Aug 2020 15:17:07 +0000 Date: Tue, 18 Aug 2020 16:17:07 +0100 From: Al Viro To: Oleg Nesterov Cc: Jann Horn , Andrew Morton , Linus Torvalds , Christoph Hellwig , linux-kernel@vger.kernel.org, linux-mm@kvack.org, linux-fsdevel@vger.kernel.org, "Eric W . Biederman" Subject: Re: [PATCH v3 2/5] coredump: Let dump_emit() bail out on short writes Message-ID: <20200818151707.GD1236603@ZenIV.linux.org.uk> References: <20200818061239.29091-1-jannh@google.com> <20200818061239.29091-3-jannh@google.com> <20200818134027.GF29865@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20200818134027.GF29865@redhat.com> X-Rspamd-Queue-Id: BF1C81803F780 X-Spamd-Result: default: False [0.00 / 100.00] X-Rspamd-Server: rspam03 X-Bogosity: Ham, tests=bogofilter, spamicity=0.000358, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: On Tue, Aug 18, 2020 at 03:40:28PM +0200, Oleg Nesterov wrote: > On 08/18, Jann Horn wrote: > > > > + if (dump_interrupted()) > > + return 0; > > + n = __kernel_write(file, addr, nr, &pos); > > + if (n != nr) > > + return 0; > > + file->f_pos = pos; > > Just curious, can't we simply do > > __kernel_write(file, addr, nr, &file->f_pos); > > and avoid "loff_t pos" ? Bloody bad pattern; it would be (probably) safe in this case, but in general ->f_pos is shared data. Exposing it to fuckloads of ->write() instances is a bad idea - we had bugs like that. General rule: never pass an address of ->f_pos to anything, and limit access to it as much as possible.