linux-kernel - Re: [PATCH v9 7/8] ima: check against blacklisted hashes for files with modsig

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Message-ID: <8e6dde58-17c2-a834-9ec3-1271b4ffd3a8@linux.microsoft.com>
Date:   Thu, 24 Oct 2019 10:48:19 -0700
From:   Lakshmi Ramasubramanian <nramas@...ux.microsoft.com>
To:     Nayna Jain <nayna@...ux.ibm.com>, linuxppc-dev@...abs.org,
        linux-efi@...r.kernel.org, linux-integrity@...r.kernel.org
Cc:     linux-kernel@...r.kernel.org,
        Michael Ellerman <mpe@...erman.id.au>,
        Benjamin Herrenschmidt <benh@...nel.crashing.org>,
        Paul Mackerras <paulus@...ba.org>,
        Ard Biesheuvel <ard.biesheuvel@...aro.org>,
        Jeremy Kerr <jk@...abs.org>,
        Matthew Garret <matthew.garret@...ula.com>,
        Mimi Zohar <zohar@...ux.ibm.com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Claudio Carvalho <cclaudio@...ux.ibm.com>,
        George Wilson <gcwilson@...ux.ibm.com>,
        Elaine Palmer <erpalmer@...ibm.com>,
        Eric Ricther <erichte@...ux.ibm.com>,
        Oliver O'Halloran <oohall@...il.com>,
        Prakhar Srivastava <prsriva02@...il.com>
Subject: Re: [PATCH v9 7/8] ima: check against blacklisted hashes for files
 with modsig

On 10/23/2019 8:47 PM, Nayna Jain wrote:

> +/*
> + * ima_check_blacklist - determine if the binary is blacklisted.
> + *
> + * Add the hash of the blacklisted binary to the measurement list, based
> + * on policy.
> + *
> + * Returns -EPERM if the hash is blacklisted.
> + */
> +int ima_check_blacklist(struct integrity_iint_cache *iint,
> +			const struct modsig *modsig, int pcr)
> +{
> +	enum hash_algo hash_algo;
> +	const u8 *digest = NULL;
> +	u32 digestsize = 0;
> +	int rc = 0;
> +
> +	if (!(iint->flags & IMA_CHECK_BLACKLIST))
> +		return 0;
> +
> +	if (iint->flags & IMA_MODSIG_ALLOWED && modsig) {
> +		ima_get_modsig_digest(modsig, &hash_algo, &digest, &digestsize);
> +
> +		rc = is_binary_blacklisted(digest, digestsize);
> +		if ((rc == -EPERM) && (iint->flags & IMA_MEASURE))
> +			process_buffer_measurement(digest, digestsize,
> +						   "blacklisted-hash", NONE,
> +						   pcr);
> +	}

The enum value "NONE" is being passed to process_buffer_measurement to 
indicate that the check for required action based on ima policy is 
already done by ima_check_blacklist. Not sure, but this can cause 
confusion in the future when someone updates process_buffer_measurement.

Would it instead be better to add another parameter to 
process_buffer_measurement to indicate the above condition?

  -lakshmi