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=-4.7 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH, MAILING_LIST_MULTI,SPF_PASS,URIBL_BLOCKED autolearn=ham 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 3B9E3C43441 for ; Wed, 14 Nov 2018 11:46:32 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id EC5212086A for ; Wed, 14 Nov 2018 11:46:31 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=oracle.com header.i=@oracle.com header.b="Xr+s3A/n" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org EC5212086A Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=oracle.com Authentication-Results: mail.kernel.org; spf=none smtp.mailfrom=linux-kernel-owner@vger.kernel.org Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1731846AbeKNVtY (ORCPT ); Wed, 14 Nov 2018 16:49:24 -0500 Received: from userp2120.oracle.com ([156.151.31.85]:56122 "EHLO userp2120.oracle.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1727758AbeKNVtY (ORCPT ); Wed, 14 Nov 2018 16:49:24 -0500 Received: from pps.filterd (userp2120.oracle.com [127.0.0.1]) by userp2120.oracle.com (8.16.0.22/8.16.0.22) with SMTP id wAEBiBHt041514; Wed, 14 Nov 2018 11:46:21 GMT DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=oracle.com; h=content-type : mime-version : subject : from : in-reply-to : date : cc : content-transfer-encoding : message-id : references : to; s=corp-2018-07-02; bh=wau0gGAVNLyYp+1AedDjz3rJQSwsbnKSZcLCLZkH7Mc=; b=Xr+s3A/nbHR3uzgEe4wPfLi97ECNdGGl+wNpkJrtvcd7oKMw6Grw7B7PWeAwKGCa7iAD XnBDYgqwgzDAy1ZEjg4kXnNVbdl7HDIW60fVsiGsK1p/RpxZCMAPo0Zf+isk9iTKLDHG mR3KYbzlzVB2rwRlwuLIhsmJ8V4dRxCWGkQKb9n6bs/zIQ48J1JkjYfC7G42m7M/LdBD 2zcK+hTuv1sRAaLFn+8XhjRWbvU7mE44YvcqVNi2HPmVteNd4YzfUqufbYvBou23PMvx B5a0QwJmDlqEPYrj2hHcvuHhqjotLgAiEEOuhb36c/QNYy/ethxW6VAboEl6UehezYMp FA== Received: from userv0021.oracle.com (userv0021.oracle.com [156.151.31.71]) by userp2120.oracle.com with ESMTP id 2nr7cs2wuj-1 (version=TLSv1.2 cipher=ECDHE-RSA-AES256-GCM-SHA384 bits=256 verify=OK); Wed, 14 Nov 2018 11:46:21 +0000 Received: from userv0121.oracle.com (userv0121.oracle.com [156.151.31.72]) by userv0021.oracle.com (8.14.4/8.14.4) with ESMTP id wAEBkKAV020641 (version=TLSv1/SSLv3 cipher=DHE-RSA-AES256-GCM-SHA384 bits=256 verify=OK); Wed, 14 Nov 2018 11:46:20 GMT Received: from abhmp0008.oracle.com (abhmp0008.oracle.com [141.146.116.14]) by userv0121.oracle.com (8.14.4/8.13.8) with ESMTP id wAEBkJRe028043; Wed, 14 Nov 2018 11:46:19 GMT Received: from [192.168.0.110] (/73.243.10.6) by default (Oracle Beehive Gateway v4.0) with ESMTP ; Wed, 14 Nov 2018 03:46:19 -0800 Content-Type: text/plain; charset=us-ascii Mime-Version: 1.0 (Mac OS X Mail 12.2 \(3445.102.3\)) Subject: Re: [PATCH] mm/usercopy: Use memory range to be accessed for wraparound check From: William Kucharski In-Reply-To: <5dcd06a0f84a4824bb9bab2b437e190d@AcuMS.aculab.com> Date: Wed, 14 Nov 2018 04:46:18 -0700 Cc: "Isaac J. Manjarres" , Kees Cook , "crecklin@redhat.com" , "linux-mm@kvack.org" , "linux-kernel@vger.kernel.org" , "psodagud@codeaurora.org" , "tsoni@codeaurora.org" , "stable@vger.kernel.org" Content-Transfer-Encoding: quoted-printable Message-Id: <7C54170F-DE66-47E0-9C0D-7D1A97DCD339@oracle.com> References: <1542156686-12253-1-git-send-email-isaacm@codeaurora.org> <5dcd06a0f84a4824bb9bab2b437e190d@AcuMS.aculab.com> To: David Laight X-Mailer: Apple Mail (2.3445.102.3) X-Proofpoint-Virus-Version: vendor=nai engine=5900 definitions=9076 signatures=668683 X-Proofpoint-Spam-Details: rule=notspam policy=default score=0 suspectscore=0 malwarescore=0 phishscore=0 bulkscore=0 spamscore=0 mlxscore=0 mlxlogscore=995 adultscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.0.1-1810050000 definitions=main-1811140108 Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org > On Nov 14, 2018, at 4:09 AM, David Laight = wrote: >=20 > From: William Kucharski >> Sent: 14 November 2018 10:35 >>=20 >>> On Nov 13, 2018, at 5:51 PM, Isaac J. Manjarres = wrote: >>>=20 >>> diff --git a/mm/usercopy.c b/mm/usercopy.c >>> index 852eb4e..0293645 100644 >>> --- a/mm/usercopy.c >>> +++ b/mm/usercopy.c >>> @@ -151,7 +151,7 @@ static inline void check_bogus_address(const = unsigned long ptr, unsigned long n, >>> bool to_user) >>> { >>> /* Reject if object wraps past end of memory. */ >>> - if (ptr + n < ptr) >>> + if (ptr + (n - 1) < ptr) >>> usercopy_abort("wrapped address", NULL, to_user, 0, ptr = + n); >>=20 >> I'm being paranoid, but is it possible this routine could ever be = passed "n" set to zero? >>=20 >> If so, it will erroneously abort indicating a wrapped address as (n - = 1) wraps to ULONG_MAX. >>=20 >> Easily fixed via: >>=20 >> if ((n !=3D 0) && (ptr + (n - 1) < ptr)) >=20 > Ugg... you don't want a double test. >=20 > I'd guess that a length of zero is likely, but a usercopy that = includes > the highest address is going to be invalid because it is a kernel = address > (on most archs, and probably illegal on others). > What you really want to do is add 'ptr + len' and check the carry = flag. The extra test is only a few extra instructions, but I understand the = concern. (Though I don't know how you'd access the carry flag from C in a machine-independent = way. Also, for the calculation to be correct you still need to check 'ptr + (len - 1)' for = the wrap.) You could also theoretically call gcc's __builtin_uadd_overflow() if you = want to get carried away. As I mentioned, I was just being paranoid, but the passed zero length = issue stood out to me. William Kucharski=