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From: Mimi Zohar <zohar@linux.ibm.com>
To: Roberto Sassu <roberto.sassu@huawei.com>,
	"jarkko.sakkinen@linux.intel.com"
	<jarkko.sakkinen@linux.intel.com>,
	"james.bottomley@hansenpartnership.com" 
	<james.bottomley@hansenpartnership.com>,
	"linux-integrity@vger.kernel.org"
	<linux-integrity@vger.kernel.org>
Cc: "linux-security-module@vger.kernel.org" 
	<linux-security-module@vger.kernel.org>,
	"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
	Silviu Vlasceanu <Silviu.Vlasceanu@huawei.com>
Subject: Re: [PATCH 7/8] ima: use ima_hash_algo for collision detection in the measurement list
Date: Fri, 31 Jan 2020 09:22:05 -0500
Message-ID: <1580480525.6104.88.camel@linux.ibm.com> (raw)
In-Reply-To: <44c1b3f6d3fe414e914317ef8e5c6f8f@huawei.com>

On Fri, 2020-01-31 at 14:02 +0000, Roberto Sassu wrote:
> > -----Original Message-----
> > From: linux-integrity-owner@vger.kernel.org [mailto:linux-integrity-
> > owner@vger.kernel.org] On Behalf Of Mimi Zohar
> > Sent: Thursday, January 30, 2020 11:26 PM
> > To: Roberto Sassu <roberto.sassu@huawei.com>;
> > jarkko.sakkinen@linux.intel.com;
> > james.bottomley@hansenpartnership.com; linux-integrity@vger.kernel.org
> > Cc: linux-security-module@vger.kernel.org; linux-kernel@vger.kernel.org;
> > Silviu Vlasceanu <Silviu.Vlasceanu@huawei.com>
> > Subject: Re: [PATCH 7/8] ima: use ima_hash_algo for collision detection in
> > the measurement list
> > 
> > On Mon, 2020-01-27 at 18:04 +0100, Roberto Sassu wrote:
> > > Before calculating a digest for each PCR bank, collisions were detected
> > > with a SHA1 digest. This patch includes ima_hash_algo among the
> > algorithms
> > > used to calculate the template digest and checks collisions on that digest.
> > >
> > > Signed-off-by: Roberto Sassu <roberto.sassu@huawei.com>
> > 
> > Definitely needed to protect against a sha1 collision attack.
> > 
> > <snip>
> > 
> > >
> > > diff --git a/security/integrity/ima/ima_api.c
> > b/security/integrity/ima/ima_api.c
> > > index ebaf0056735c..a9bb45de6db9 100644
> > > --- a/security/integrity/ima/ima_api.c
> > > +++ b/security/integrity/ima/ima_api.c
> > > @@ -51,7 +51,7 @@ int ima_alloc_init_template(struct ima_event_data
> > *event_data,
> > >  	if (!*entry)
> > >  		return -ENOMEM;
> > >
> > > -	(*entry)->digests = kcalloc(ima_tpm_chip->nr_allocated_banks + 1,
> > > +	(*entry)->digests = kcalloc(ima_tpm_chip->nr_allocated_banks + 2,
> > >  				    sizeof(*(*entry)->digests), GFP_NOFS);
> > >  	if (!(*entry)->digests) {
> > >  		result = -ENOMEM;
> > 
> > I would prefer not having to allocate and use "nr_allocated_banks + 1"
> > everywhere, but I understand the need for it.  I'm not sure this patch
> > warrants allocating +2.  Perhaps, if a TPM bank doesn't exist for the
> > IMA default hash algorithm, use a different algorithm or, worst case,
> > continue using the ima_sha1_idx.
> 
> We could introduce a new option called ima_hash_algo_tpm to specify
> the algorithm of an allocated bank. We can use this for boot_aggregate
> and hash collision detection.

I don't think that would work in the case where the IMA default hash
is set to sha256, but the system has a TPM 1.2 chip.  We would be left
using SHA1 for the file hash collision detection.

With my suggestion of defining an "extra" variable, I kind of back
tracked here.  There are two problems that I'm trying to address -
hard coding the number of additional "banks" and unnecessarily
allocating more memory than necessary.  By pre-walking the list,
calculating the "extra" banks, you'll resolve both issues.

Mimi


  reply index

Thread overview: 26+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-01-27 17:04 [PATCH 0/8] ima: support stronger algorithms for attestation Roberto Sassu
2020-01-27 17:04 ` [PATCH 1/8] tpm: initialize crypto_id of allocated_banks to HASH_ALGO__LAST Roberto Sassu
2020-01-29  8:39   ` Petr Vorel
2020-01-30  8:47   ` Jarkko Sakkinen
2020-01-30 16:11     ` Roberto Sassu
2020-01-31 13:33       ` Mimi Zohar
2020-02-01 17:10         ` Jarkko Sakkinen
2020-01-27 17:04 ` [PATCH 2/8] ima: evaluate error in init_ima() Roberto Sassu
2020-01-31 13:33   ` Mimi Zohar
2020-01-27 17:04 ` [PATCH 3/8] ima: store template digest directly in ima_template_entry Roberto Sassu
2020-01-27 17:04 ` [PATCH 4/8] ima: switch to dynamically allocated buffer for template digests Roberto Sassu
2020-01-27 17:04 ` [PATCH 5/8] ima: allocate and initialize tfm for each PCR bank Roberto Sassu
2020-01-31 12:18   ` Mimi Zohar
2020-01-31 13:42     ` Roberto Sassu
2020-01-31 13:58       ` Mimi Zohar
2020-01-27 17:04 ` [PATCH 6/8] ima: calculate and extend PCR with digests in ima_template_entry Roberto Sassu
2020-01-27 17:29   ` Roberto Sassu
2020-01-27 17:04 ` [PATCH 7/8] ima: use ima_hash_algo for collision detection in the measurement list Roberto Sassu
2020-01-30 22:26   ` Mimi Zohar
2020-01-31 14:02     ` Roberto Sassu
2020-01-31 14:22       ` Mimi Zohar [this message]
2020-01-31 14:41         ` Roberto Sassu
2020-01-31 14:50           ` Mimi Zohar
2020-01-27 17:04 ` [PATCH 8/8] ima: switch to ima_hash_algo for boot aggregate Roberto Sassu
2020-01-31 15:21   ` Roberto Sassu
2020-01-30 22:26 ` [PATCH 0/8] ima: support stronger algorithms for attestation Mimi Zohar

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