From mboxrd@z Thu Jan 1 00:00:00 1970 From: Pavel Machek Subject: Re: [PATCH 3/4] add ksm kernel shared memory driver. Date: Wed, 3 Dec 2008 15:33:08 +0100 Message-ID: <20081203143307.GA2068@ucw.cz> 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> <20081202181333.38c7b421@lxorguk.ukuu.org.uk> <20081202212411.GG17607@acer.localdomain> <20081202221029.513e8774@lxorguk.ukuu.org.uk> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Return-path: Content-Disposition: inline In-Reply-To: <20081202221029.513e8774@lxorguk.ukuu.org.uk> Sender: kvm-owner@vger.kernel.org To: Alan Cox Cc: Chris Wright , Izik Eidus , akpm@linux-foundation.org, linux-kernel@vger.kernel.org, linux-mm@kvack.org, kvm@vger.kernel.org, aarcange@redhat.com, avi@redhat.com, dlaor@redhat.com, kamezawa.hiroyu@jp.fujitsu.com, cl@linux-foundation.org, corbet@lwn.net List-Id: linux-mm.kvack.org On Tue 2008-12-02 22:10:29, Alan Cox wrote: > On Tue, 2 Dec 2008 13:24:11 -0800 > Chris Wright wrote: > > > * Alan Cox (alan@lxorguk.ukuu.org.uk) wrote: > > > 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. > > > > And, just to clarify, your concern would extend to any digest based > > comparison? Or are you specifically concerned about sha1? > > Taken off list Hmmm, list would like to know :-). -- (english) http://www.livejournal.com/~pavelmachek (cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html