Messages in this thread | | | Date | Tue, 2 Dec 2008 13:24:11 -0800 | From | Chris Wright <> | Subject | Re: [PATCH 3/4] add ksm kernel shared memory driver. |
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* Alan Cox (alan@lxorguk.ukuu.org.uk) wrote: > On Tue, 2 Dec 2008 10:07:24 -0800 > Chris Wright <chrisw@redhat.com> 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?
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