linux-kernel - Re: [PATCH 3/4] add ksm kernel shared memory driver.

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Date:	Fri, 28 Nov 2008 16:58:06 +0000
From:	Alan Cox <alan@...rguk.ukuu.org.uk>
To:	Izik Eidus <ieidus@...hat.com>
Cc:	akpm@...ux-foundation.org, linux-kernel@...r.kernel.org,
	linux-mm@...ck.org, kvm@...r.kernel.org, aarcange@...hat.com,
	chrisw@...hat.com, avi@...hat.com, dlaor@...hat.com,
	kamezawa.hiroyu@...fujitsu.com, cl@...ux-foundation.org,
	corbet@....net, ieidus@...hat.com
Subject: Re: [PATCH 3/4] add ksm kernel shared memory driver.

> +	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.
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