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

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Date:   Tue, 4 Dec 2018 16:09:10 -0800
From:   Jarkko Sakkinen <jarkko.sakkinen@...ux.intel.com>
To:     Roberto Sassu <roberto.sassu@...wei.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 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.

/Jarkko