From mboxrd@z Thu Jan 1 00:00:00 1970 From: Chris Wright Subject: Re: [PATCH 3/4] add ksm kernel shared memory driver. Date: Tue, 2 Dec 2008 10:07:24 -0800 Message-ID: <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> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii 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 To: Alan Cox Return-path: Received: from mx2.redhat.com ([66.187.237.31]:44104 "EHLO mx2.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752332AbYLBSIQ (ORCPT ); Tue, 2 Dec 2008 13:08:16 -0500 Content-Disposition: inline In-Reply-To: <20081128165806.172d1026@lxorguk.ukuu.org.uk> Sender: kvm-owner@vger.kernel.org List-ID: * 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. thanks, -chris