* Alan Cox ([EMAIL PROTECTED]) wrote:
> On Tue, 2 Dec 2008 10:07:24 -0800
> Chris Wright <[EMAIL PROTECTED]> wrote:
> > * Alan Cox ([EMAIL PROTECTED]) 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?
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