linux-kernel - Re: [PATCH v6 6/7] tpm: ensure that the output of PCR read contains the correct digest size

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Message-ID: <af5a430f-c6ef-3989-0d93-7f972c26737d@huawei.com>
Date:   Thu, 6 Dec 2018 19:07:34 +0100
From:   Roberto Sassu <roberto.sassu@...wei.com>
To:     Jarkko Sakkinen <jarkko.sakkinen@...ux.intel.com>
CC:     <zohar@...ux.ibm.com>, <david.safford@...com>,
        <monty.wiseman@...com>, <linux-integrity@...r.kernel.org>,
        <linux-security-module@...r.kernel.org>,
        <linux-kernel@...r.kernel.org>, <silviu.vlasceanu@...wei.com>
Subject: Re: [PATCH v6 6/7] tpm: ensure that the output of PCR read contains
 the correct digest size

On 12/5/2018 1:46 AM, Jarkko Sakkinen wrote:
> On Tue, Dec 04, 2018 at 04:09:10PM -0800, Jarkko Sakkinen wrote:
>> On Tue, Dec 04, 2018 at 09:21:37AM +0100, Roberto Sassu wrote:
>>>   	out = (struct tpm2_pcr_read_out *)&buf.data[TPM_HEADER_SIZE];
>>>   	digest_size = be16_to_cpu(out->digest_size);
>>> -	if (digest_size > sizeof(digest->digest)) {
>>> +	if (digest_size > sizeof(digest->digest) ||
>>> +	    (!digest_size_ptr && digest_size != expected_digest_size)) {
>>>   		rc = -EINVAL;
>>>   		goto out;
>>>   	}
>>
>> Just noticed this but you must squash 4-6 because applying only
>> previous commits will result a broken tree. It will be much bigger
>> commit but won't be broken.
>>
>> I think you should also feed min_rsp_body_length as you should be
>> able to precalculate.
>>
>> Last time I was asking why this isn't a bug fix. It is even for
>> the existing code. The existing code should have a bug fix that
>> checks that the received digest size so that it is the expected
>> SHA1 size before we can apply this commit.
> 
> My bad. This is not the same deal as the code because in the old code we
> always copy a constant block. Here we use the variable as parameter for
> memcpy() so it is better to check the size. You can ignore the last
> paragraph completely. Sorry, had to double check this one.
> 
> There is no need to do any type of bug fix for the current tree.
> 
> Still 4-6 need to be squashed in order to not put purposely the tree
> into broken state.

Ok. I keep the description of 5, and add few details from 4 and 6.

Roberto


> /Jarko
> 

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