From: Thiago Jung Bauermann <bauerman@linux.vnet.ibm.com>
To: Mimi Zohar <zohar@linux.vnet.ibm.com>
Cc: linux-integrity@vger.kernel.org,
linux-security-module@vger.kernel.org, keyrings@vger.kernel.org,
linux-crypto@vger.kernel.org, linuxppc-dev@lists.ozlabs.org,
linux-kernel@vger.kernel.org,
Dmitry Kasatkin <dmitry.kasatkin@gmail.com>,
James Morris <james.l.morris@oracle.com>,
"Serge E. Hallyn" <serge@hallyn.com>,
David Howells <dhowells@redhat.com>,
David Woodhouse <dwmw2@infradead.org>,
Jessica Yu <jeyu@redhat.com>,
Rusty Russell <rusty@rustcorp.com.au>,
Herbert Xu <herbert@gondor.apana.org.au>,
"David S. Miller" <davem@davemloft.net>, "AKASHI\,
Takahiro" <takahiro.akashi@linaro.org>
Subject: Re: [PATCH v5 18/18] ima: Write modsig to the measurement list
Date: Thu, 26 Oct 2017 20:02:23 -0200 [thread overview]
Message-ID: <87r2tpwosw.fsf@linux.vnet.ibm.com> (raw)
In-Reply-To: <1509048454.5886.108.camel@linux.vnet.ibm.com>
Hello Mimi,
Thanks for your review.
Mimi Zohar <zohar@linux.vnet.ibm.com> writes:
> On Tue, 2017-10-17 at 22:53 -0200, Thiago Jung Bauermann wrote:
>
>> diff --git a/security/integrity/ima/ima_main.c b/security/integrity/ima/ima_main.c
>> index 6a2d960fbd92..0d3390de7432 100644
>> --- a/security/integrity/ima/ima_main.c
>> +++ b/security/integrity/ima/ima_main.c
>> @@ -246,7 +246,35 @@ static int process_measurement(struct file *file, char *buf, loff_t size,
>> rc = ima_appraise_measurement(func, iint, file, buf, size,
>> pathname, &xattr_value,
>> &xattr_len, opened);
>> - if (action & IMA_MEASURE)
>> +
>> + /*
>> + * MODSIG has one corner case we need to deal with here:
>> + *
>> + * Suppose the policy has one measure rule for one hook and an appraise
>> + * rule for a different hook. Suppose also that the template requires
>> + * the signature to be stored in the measurement list.
>> + *
>> + * If a file containing a MODSIG is measured by the first hook before
>> + * being appraised by the second one, the corresponding entry in the
>> + * measurement list will not contain the MODSIG because we only fetch it
>> + * for IMA_APPRAISAL. We don't fetch it earlier because if the file has
>> + * both a DIGSIG and a MODSIG it's not possible to know which one will
>> + * be valid without actually doing the appraisal.
>> + *
>> + * Therefore, after appraisal of a MODSIG signature we need to store the
>> + * measurement again if the current template requires storing the
>> + * signature.
>
> Yes, all true, but this long comment doesn't belong here in the middle
> of process_measurement().
>
>> + * With the opposite ordering (the appraise rule triggering before the
>> + * measurement rule) there is the same problem but it's not possible to
>> + * do anything about it because at the time we are appraising the
>> + * signature it's impossible to know whether a measurement will ever
>> + * need to be stored for this file.
>> + */
>
> With the template format "ima-sig", the verified file signature needs
> to be included in the measurement list. Based on this file signature,
> the attestation server can validate the signature.
>
> In this case, where the appraisal comes first followed by the
> measurement, the appraised file signature is included in the
> measurement list. I don't see the problem here.
I think I forgot that during appraisal the modsig is copied into the
iint cache and that it will be used when the measure rule is trigerred.
I'll drop that last paragraph.
>
>> + if ((action & IMA_MEASURE) || ((iint->flags & IMA_MEASURE) &&
>> + xattr_value &&
>> + xattr_value->type == IMA_MODSIG &&
>> + ima_current_template_has_sig()))
>
> Like the clean up you did elsewhere, this new set of tests should be
> made into a function. The comment could placed along with the new
> function.
Ok. I didn't create a function because these tests are only done here,
but I agree that it will make the code clearer, and be a better place
for the big comment as well. Will do in the next version.
--
Thiago Jung Bauermann
IBM Linux Technology Center
next prev parent reply other threads:[~2017-10-26 22:02 UTC|newest]
Thread overview: 27+ messages / expand[flat|nested] mbox.gz Atom feed top
2017-10-18 0:53 [PATCH v5 00/18] Appended signatures support for IMA appraisal Thiago Jung Bauermann
2017-10-18 0:53 ` [PATCH v5 01/18] ima: Remove redundant conditional operator Thiago Jung Bauermann
2017-10-18 0:53 ` [PATCH v5 02/18] ima: Remove some superfluous parentheses Thiago Jung Bauermann
2017-10-18 0:53 ` [PATCH v5 03/18] evm, ima: Remove " Thiago Jung Bauermann
2017-10-18 0:53 ` [PATCH v5 04/18] evm, ima: Remove more " Thiago Jung Bauermann
2017-10-18 0:53 ` [PATCH v5 05/18] ima: Simplify ima_eventsig_init Thiago Jung Bauermann
2017-10-18 0:53 ` [PATCH v5 06/18] ima: Improvements in ima_appraise_measurement Thiago Jung Bauermann
2017-10-18 0:53 ` [PATCH v5 07/18] integrity: Introduce struct evm_xattr Thiago Jung Bauermann
2017-10-18 0:53 ` [PATCH v5 08/18] integrity: Select CONFIG_KEYS instead of depending on it Thiago Jung Bauermann
2017-10-18 0:53 ` [PATCH v5 09/18] ima: Don't pass xattr value to EVM xattr verification Thiago Jung Bauermann
2017-10-18 0:53 ` [PATCH v5 10/18] ima: Store measurement after appraisal Thiago Jung Bauermann
2017-10-18 0:53 ` [PATCH v5 11/18] ima: Export func_tokens Thiago Jung Bauermann
2017-10-18 0:53 ` [PATCH v5 12/18] MODSIGN: Export module signature definitions Thiago Jung Bauermann
2017-10-26 20:12 ` Mimi Zohar
2017-10-26 22:47 ` Thiago Jung Bauermann
2017-10-26 23:13 ` Mimi Zohar
2017-10-18 0:53 ` [PATCH v5 13/18] PKCS#7: Introduce pkcs7_get_message_sig and verify_pkcs7_message_sig Thiago Jung Bauermann
2017-10-26 20:12 ` Mimi Zohar
2017-10-18 0:53 ` [PATCH v5 14/18] integrity: Introduce integrity_keyring_from_id Thiago Jung Bauermann
2017-10-18 0:53 ` [PATCH v5 15/18] ima: Add modsig appraise_type option for module-style appended signatures Thiago Jung Bauermann
2017-10-18 0:53 ` [PATCH v5 16/18] ima: Add functions to read and verify a modsig signature Thiago Jung Bauermann
2017-10-18 0:53 ` [PATCH v5 17/18] ima: Implement support for module-style appended signatures Thiago Jung Bauermann
2017-10-31 13:31 ` Mimi Zohar
2017-10-18 0:53 ` [PATCH v5 18/18] ima: Write modsig to the measurement list Thiago Jung Bauermann
2017-10-26 20:07 ` Mimi Zohar
2017-10-26 22:02 ` Thiago Jung Bauermann [this message]
2017-10-26 20:53 ` [PATCH v5 00/18] Appended signatures support for IMA appraisal Mimi Zohar
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