Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755349AbYLBSOd (ORCPT ); Tue, 2 Dec 2008 13:14:33 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1752571AbYLBSOU (ORCPT ); Tue, 2 Dec 2008 13:14:20 -0500 Received: from earthlight.etchedpixels.co.uk ([81.2.110.250]:34010 "EHLO lxorguk.ukuu.org.uk" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1752762AbYLBSOT (ORCPT ); Tue, 2 Dec 2008 13:14:19 -0500 Date: Tue, 2 Dec 2008 18:13:33 +0000 From: Alan Cox To: Chris Wright Cc: Izik Eidus , akpm@linux-foundation.org, linux-kernel@vger.kernel.org, linux-mm@kvack.org, kvm@vger.kernel.org, aarcange@redhat.com, chrisw@redhat.com, avi@redhat.com, dlaor@redhat.com, kamezawa.hiroyu@jp.fujitsu.com, cl@linux-foundation.org, corbet@lwn.net Subject: Re: [PATCH 3/4] add ksm kernel shared memory driver. Message-ID: <20081202181333.38c7b421@lxorguk.ukuu.org.uk> In-Reply-To: <20081202180724.GC17607@acer.localdomain> References: <1226888432-3662-1-git-send-email-ieidus@redhat.com> <1226888432-3662-2-git-send-email-ieidus@redhat.com> <1226888432-3662-3-git-send-email-ieidus@redhat.com> <1226888432-3662-4-git-send-email-ieidus@redhat.com> <20081128165806.172d1026@lxorguk.ukuu.org.uk> <20081202180724.GC17607@acer.localdomain> X-Mailer: Claws Mail 3.5.0 (GTK+ 2.12.12; x86_64-redhat-linux-gnu) Organization: Red Hat UK Cyf., Amberley Place, 107-111 Peascod Street, Windsor, Berkshire, SL4 1TE, Y Deyrnas Gyfunol. Cofrestrwyd yng Nghymru a Lloegr o'r rhif cofrestru 3798903 Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1190 Lines: 29 On Tue, 2 Dec 2008 10:07:24 -0800 Chris Wright wrote: > * Alan Cox (alan@lxorguk.ukuu.org.uk) wrote: > > > + r = !memcmp(old_digest, sha1_item->sha1val, SHA1_DIGEST_SIZE); > > > + mutex_unlock(&sha1_lock); > > > + if (r) { > > > + char *old_addr, *new_addr; > > > + old_addr = kmap_atomic(oldpage, KM_USER0); > > > + new_addr = kmap_atomic(newpage, KM_USER1); > > > + r = !memcmp(old_addr+PAGEHASH_LEN, new_addr+PAGEHASH_LEN, > > > + PAGE_SIZE-PAGEHASH_LEN); > > > > NAK - this isn't guaranteed to be robust so you could end up merging > > different pages one provided by a malicious attacker. > > I presume you're referring to the digest comparison. While there's > theoretical concern of hash collision, it's mitigated by hmac(sha1) > so the attacker can't brute force for known collisions. Using current known techniques. A random collision is just as bad news. This code simply isn't fit for the kernel. -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/