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SubjectRe: [PATCH 3/4] add ksm kernel shared memory driver.
* 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


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