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=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SIGNED_OFF_BY, 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 49852C33CB2 for ; Fri, 31 Jan 2020 06:13:42 +0000 (UTC) Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by mail.kernel.org (Postfix) with ESMTP id 0983B2082E for ; Fri, 31 Jan 2020 06:13:42 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (1024-bit key) header.d=kernel.org header.i=@kernel.org header.b="HBgPnME3" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 0983B2082E Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=linux-foundation.org Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=owner-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix) id 7E24B6B0517; Fri, 31 Jan 2020 01:13:41 -0500 (EST) Received: by kanga.kvack.org (Postfix, from userid 40) id 71B3B6B0519; Fri, 31 Jan 2020 01:13:41 -0500 (EST) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 547346B051A; Fri, 31 Jan 2020 01:13:41 -0500 (EST) X-Delivered-To: linux-mm@kvack.org Received: from forelay.hostedemail.com (smtprelay0147.hostedemail.com [216.40.44.147]) by kanga.kvack.org (Postfix) with ESMTP id 3A3736B0517 for ; Fri, 31 Jan 2020 01:13:41 -0500 (EST) Received: from smtpin25.hostedemail.com (10.5.19.251.rfc1918.com [10.5.19.251]) by forelay01.hostedemail.com (Postfix) with ESMTP id E43EF180AD804 for ; Fri, 31 Jan 2020 06:13:40 +0000 (UTC) X-FDA: 76436913000.25.anger65_201a9b9f64b2f X-HE-Tag: anger65_201a9b9f64b2f X-Filterd-Recvd-Size: 3661 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by imf29.hostedemail.com (Postfix) with ESMTP for ; Fri, 31 Jan 2020 06:13:40 +0000 (UTC) Received: from localhost.localdomain (c-73-231-172-41.hsd1.ca.comcast.net [73.231.172.41]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPSA id 9F6272173E; Fri, 31 Jan 2020 06:13:39 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1580451219; bh=83wkJTEy+jfQkyxfhaDsa2KpvkFrSWUHKlWkpSyHzRc=; h=Date:From:To:Subject:In-Reply-To:From; b=HBgPnME3YvEx+toiIndjvhWhYePlt7o82wm6/GJf+qQGr6DfM+oSYDqaeftguf1C/ 7765NtMIr0KuDSXfRQsGsqpB8ossUVlspyPutquccDJJSxd3uiFfz8pzBWm5bIAWU0 w0IpsGYzOwDtdExPwmKjaIDHl6lzcvLtoy6RJHqY= Date: Thu, 30 Jan 2020 22:13:39 -0800 From: Andrew Morton To: akpm@linux-foundation.org, hughd@google.com, jannh@google.com, keescook@chromium.org, linux-mm@kvack.org, mm-commits@vger.kernel.org, torvalds@linux-foundation.org, viro@zeniv.linux.org.uk, vvs@virtuozzo.com Subject: [patch 046/118] mm/swapfile.c: swap_next should increase position index Message-ID: <20200131061339.vdpByFCaP%akpm@linux-foundation.org> In-Reply-To: <20200130221021.5f0211c56346d5485af07923@linux-foundation.org> User-Agent: s-nail v14.8.16 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: From: Vasily Averin Subject: mm/swapfile.c: swap_next should increase position index If seq_file .next fuction does not change position index, read after some lseek can generate unexpected output. In Aug 2018 NeilBrown noticed commit 1f4aace60b0e ("fs/seq_file.c: simplify seq_file iteration code and interface") "Some ->next functions do not increment *pos when they return NULL... Note that such ->next functions are buggy and should be fixed. A simple demonstration is dd if=/proc/swaps bs=1000 skip=1 Choose any block size larger than the size of /proc/swaps. This will always show the whole last line of /proc/swaps" Described problem is still actual. If you make lseek into middle of last output line following read will output end of last line and whole last line once again. $ dd if=/proc/swaps bs=1 # usual output Filename Type Size Used Priority /dev/dm-0 partition 4194812 97536 -2 104+0 records in 104+0 records out 104 bytes copied $ dd if=/proc/swaps bs=40 skip=1 # last line was generated twice dd: /proc/swaps: cannot skip to specified offset v/dm-0 partition 4194812 97536 -2 /dev/dm-0 partition 4194812 97536 -2 3+1 records in 3+1 records out 131 bytes copied https://bugzilla.kernel.org/show_bug.cgi?id=206283 Link: http://lkml.kernel.org/r/bd8cfd7b-ac95-9b91-f9e7-e8438bd5047d@virtuozzo.com Signed-off-by: Vasily Averin Reviewed-by: Andrew Morton Cc: Jann Horn Cc: Alexander Viro Cc: Kees Cook Cc: Hugh Dickins Signed-off-by: Andrew Morton --- mm/swapfile.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) --- a/mm/swapfile.c~swap_next-should-increase-position-index +++ a/mm/swapfile.c @@ -2737,10 +2737,10 @@ static void *swap_next(struct seq_file * else type = si->type + 1; + ++(*pos); for (; (si = swap_type_to_swap_info(type)); type++) { if (!(si->flags & SWP_USED) || !si->swap_map) continue; - ++*pos; return si; } _