From: Roberto Sassu <roberto.sassu@huawei.com>
To: Mimi Zohar <zohar@linux.ibm.com>, "mjg59@google.com" <mjg59@google.com>
Cc: "linux-integrity@vger.kernel.org"
<linux-integrity@vger.kernel.org>,
"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>,
"stable@vger.kernel.org" <stable@vger.kernel.org>
Subject: RE: [PATCH 07/11] evm: Set IMA_CHANGE_XATTR/ATTR bit if EVM_ALLOW_METADATA_WRITES is set
Date: Tue, 1 Sep 2020 11:41:56 +0000 [thread overview]
Message-ID: <7f3dd815639a44ba9b0fb532c217bd21@huawei.com> (raw)
In-Reply-To: <ae06c113ec91442e293f2466cae3dd1b81f241eb.camel@linux.ibm.com>
> From: Mimi Zohar [mailto:zohar@linux.ibm.com]
> Sent: Tuesday, September 1, 2020 1:05 PM
> On Tue, 2020-09-01 at 09:08 +0000, Roberto Sassu wrote:
> > > From: Mimi Zohar [mailto:zohar@linux.ibm.com]
> > > Sent: Monday, August 24, 2020 2:18 PM
> > > On Thu, 2020-06-18 at 18:04 +0200, Roberto Sassu wrote:
> > > > When EVM_ALLOW_METADATA_WRITES is set, EVM allows any
> operation
> > > on
> > > > metadata. Its main purpose is to allow users to freely set metadata
> when
> > > > they are protected by a portable signature, until the HMAC key is
> loaded.
> > > >
> > > > However, IMA is not notified about metadata changes and, after the
> first
> > > > appraisal, always allows access to the files without checking metadata
> > > > again.
> > >
> > > ^after the first successful appraisal
> > > >
> > > > This patch checks in evm_reset_status() if EVM_ALLOW_METADATA
> > > WRITES is
> > > > enabled and if it is, sets the IMA_CHANGE_XATTR/ATTR bits
> depending on
> > > the
> > > > operation performed. At the next appraisal, metadata are revalidated.
> > >
> > > EVM modifying IMA bits crosses the boundary between EVM and IMA.
> > > There
> > > is already an IMA post_setattr hook. IMA could reset its own bit
> > > there. If necessary EVM could export as a function it's status info.
> >
> > I wouldn't try to guess in IMA when EVM resets its status. We would have
> > to duplicate the logic to check if an EVM key is loaded, if the passed xattr
> > is a POSIX ACL, ...
>
> Agreed, but IMA could call an EVM function.
>
> >
> > I think it is better to set a flag, maybe a new one, directly in EVM, to notify
> > the integrity subsystem that iint->evm_status is no longer valid.
> >
> > If the EVM flag is set, IMA would reset the appraisal flags, as it uses
> > iint->evm_status for appraisal. We can consider to reset also the measure
> > flags when we have a template that includes file metadata.
>
> When would IMA read the EVM flag? Who would reset the flag? At what
> point would it be reset? Just as EVM shouldn't be resetting the IMA
> flag, IMA shouldn't be resetting the EVM flag.
IMA would read the flag in process_measurement() and behave similarly
to when it processes IMA_CHANGE_ATTR. The flag would be reset by
evm_verify_hmac().
Roberto
HUAWEI TECHNOLOGIES Duesseldorf GmbH, HRB 56063
Managing Director: Li Peng, Li Jian, Shi Yanli
next prev parent reply other threads:[~2020-09-01 11:42 UTC|newest]
Thread overview: 16+ messages / expand[flat|nested] mbox.gz Atom feed top
[not found] <20200618160329.1263-2-roberto.sassu@huawei.com>
2020-06-18 16:04 ` [PATCH 06/11] evm: Allow setxattr() and setattr() if metadata digest won't change Roberto Sassu
2020-08-24 12:17 ` Mimi Zohar
2020-08-31 8:51 ` Roberto Sassu
2020-06-18 16:04 ` [PATCH 07/11] evm: Set IMA_CHANGE_XATTR/ATTR bit if EVM_ALLOW_METADATA_WRITES is set Roberto Sassu
2020-08-24 12:17 ` Mimi Zohar
2020-09-01 9:08 ` Roberto Sassu
2020-09-01 11:05 ` Mimi Zohar
2020-09-01 11:41 ` Roberto Sassu [this message]
2020-09-01 12:55 ` Mimi Zohar
2020-06-18 16:04 ` [PATCH 08/11] ima: Allow imasig requirement to be satisfied by EVM portable signatures Roberto Sassu
2020-08-24 13:02 ` Mimi Zohar
2020-06-18 16:04 ` [PATCH 09/11] ima: Don't remove security.ima if file must not be appraised Roberto Sassu
2020-08-24 13:02 ` Mimi Zohar
2020-06-18 16:04 ` [PATCH 10/11] ima: Don't ignore errors from crypto_shash_update() Roberto Sassu
2020-08-24 13:02 ` Mimi Zohar
2020-06-18 16:06 ` [PATCH 11/11] ima: Remove semicolon at the end of ima_get_binary_runtime_size() Roberto Sassu
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