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=-5.8 required=3.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,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 11283C4338F for ; Fri, 20 Aug 2021 19:40:34 +0000 (UTC) Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by mail.kernel.org (Postfix) with ESMTP id 97D8D61164 for ; Fri, 20 Aug 2021 19:40:33 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.4.1 mail.kernel.org 97D8D61164 Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=HansenPartnership.com Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=kvack.org Received: by kanga.kvack.org (Postfix) id E4E766B0071; Fri, 20 Aug 2021 15:40:32 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id DFE886B0072; Fri, 20 Aug 2021 15:40:32 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id CECCC8D0001; Fri, 20 Aug 2021 15:40:32 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from forelay.hostedemail.com (smtprelay0025.hostedemail.com [216.40.44.25]) by kanga.kvack.org (Postfix) with ESMTP id B7F9F6B0071 for ; Fri, 20 Aug 2021 15:40:32 -0400 (EDT) Received: from smtpin20.hostedemail.com (10.5.19.251.rfc1918.com [10.5.19.251]) by forelay03.hostedemail.com (Postfix) with ESMTP id 6668F801F3BF for ; Fri, 20 Aug 2021 19:40:32 +0000 (UTC) X-FDA: 78496475904.20.FB6D0AB Received: from bedivere.hansenpartnership.com (bedivere.hansenpartnership.com [96.44.175.130]) by imf15.hostedemail.com (Postfix) with ESMTP id 0064ED000099 for ; Fri, 20 Aug 2021 19:40:31 +0000 (UTC) Received: from localhost (localhost [127.0.0.1]) by bedivere.hansenpartnership.com (Postfix) with ESMTP id A140A12801DB; Fri, 20 Aug 2021 12:40:27 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=hansenpartnership.com; s=20151216; t=1629488427; bh=m7pwO1nE5aq19db0pqFBeoLj6CeJBhN9nsxzrjprEGM=; h=Message-ID:Subject:From:To:Date:In-Reply-To:References:From; b=MmqJ3XZXEfMCJlAKFh2eI/5ZYNGKBfgORnXhNp0Zz7I8QwbNLAPGdES1xy51LhjVO rQScnkEoKTaMQc34aIco0fRK5nIv5TfrSq8gvxUWmL5KtI/8U5OI1KJ5HGcbYmbU5B oab87nnJpijZ65kA7FHDIJKwwQieIIrNJmAuR/dI= Received: from bedivere.hansenpartnership.com ([127.0.0.1]) by localhost (bedivere.hansenpartnership.com [127.0.0.1]) (amavisd-new, port 10024) with ESMTP id jN7dzCKAsSvP; Fri, 20 Aug 2021 12:40:27 -0700 (PDT) Received: from jarvis.int.hansenpartnership.com (unknown [IPv6:2601:600:8280:66d1::527]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by bedivere.hansenpartnership.com (Postfix) with ESMTPSA id 3077212801B4; Fri, 20 Aug 2021 12:40:27 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=hansenpartnership.com; s=20151216; t=1629488427; bh=m7pwO1nE5aq19db0pqFBeoLj6CeJBhN9nsxzrjprEGM=; h=Message-ID:Subject:From:To:Date:In-Reply-To:References:From; b=MmqJ3XZXEfMCJlAKFh2eI/5ZYNGKBfgORnXhNp0Zz7I8QwbNLAPGdES1xy51LhjVO rQScnkEoKTaMQc34aIco0fRK5nIv5TfrSq8gvxUWmL5KtI/8U5OI1KJ5HGcbYmbU5B oab87nnJpijZ65kA7FHDIJKwwQieIIrNJmAuR/dI= Message-ID: <68d2b3afd9a7ee27cdb7ec9ff7eb45342ce23c12.camel@HansenPartnership.com> Subject: Re: [PATCH] mm/secretmem: use refcount_t instead of atomic_t From: James Bottomley To: Jordy Zomer , Kees Cook Cc: linux-kernel@vger.kernel.org, Andrew Morton , linux-mm@kvack.org, Mike Rapoport Date: Fri, 20 Aug 2021 12:40:26 -0700 In-Reply-To: <209705133.1285234.1629477520318@privateemail.com> References: <20210820043339.2151352-1-jordy@pwning.systems> <0874a50b61cfaf7c817cab7344c49c1641c1fd10.camel@HansenPartnership.com> <202108200904.81ED4AA52@keescook> <209705133.1285234.1629477520318@privateemail.com> Content-Type: text/plain; charset="UTF-8" User-Agent: Evolution 3.34.4 MIME-Version: 1.0 Content-Transfer-Encoding: 7bit Authentication-Results: imf15.hostedemail.com; dkim=pass header.d=hansenpartnership.com header.s=20151216 header.b=MmqJ3XZX; dkim=pass header.d=hansenpartnership.com header.s=20151216 header.b=MmqJ3XZX; dmarc=pass (policy=none) header.from=HansenPartnership.com; spf=pass (imf15.hostedemail.com: domain of James.Bottomley@HansenPartnership.com designates 96.44.175.130 as permitted sender) smtp.mailfrom=James.Bottomley@HansenPartnership.com X-Rspamd-Server: rspam02 X-Rspamd-Queue-Id: 0064ED000099 X-Stat-Signature: hps69fogmgohxqsu8nidgzifjht3xyo5 X-HE-Tag: 1629488431-617818 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 Fri, 2021-08-20 at 12:38 -0400, Jordy Zomer wrote: > Hi There! > > Because this is a global variable, it appears to be exploitable. > Either we generate a sufficient number of processes to achieve this > counter, or you increase the open file limit with ulimit or sysctl. > Unless the kernel has a hard restriction on the number of potential > file descriptors that I'm not aware of. There's no direct global counter for file descriptors, no; however, there is an indirect limit: the number of processes per user which is now defaulting to around 65535, so even a fork bomb opening the max number of fds won't get you a wrap. > In any case, it's probably a good idea to patch this to make it > explicitly secure. If you discover a hard-limit in the kernel for > open file descriptors, please let me know. I'm genuinely interested > :D! I didn't disagree it might be a useful think to update ... I just didn't think it was currently exploitable. James