Messages in this thread | | | Date | Tue, 2 Dec 2008 10:07:24 -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: > > + 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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