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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-fsdevel@vger.kernel.org" <linux-fsdevel@vger.kernel.org>,
	"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
	Christian Brauner <christian.brauner@ubuntu.com>,
	Andreas Gruenbacher <agruenba@redhat.com>
Subject: RE: [PATCH v5 09/12] evm: Allow setxattr() and setattr() for unmodified metadata
Date: Mon, 3 May 2021 15:32:52 +0000
Message-ID: <b0bfaf2352b045dfaf443ae3af73b60e@huawei.com> (raw)
In-Reply-To: <cf12878833c82710ad4356e7d023cf51241f3cc8.camel@linux.ibm.com>

> From: Mimi Zohar [mailto:zohar@linux.ibm.com]
> Sent: Monday, May 3, 2021 5:26 PM
> On Mon, 2021-05-03 at 15:11 +0000, Roberto Sassu wrote:
> > > From: Mimi Zohar [mailto:zohar@linux.ibm.com]
> > > Sent: Monday, May 3, 2021 3:00 PM
> > > On Wed, 2021-04-07 at 12:52 +0200, Roberto Sassu wrote:
> > >
> > > > diff --git a/security/integrity/evm/evm_main.c
> > > b/security/integrity/evm/evm_main.c
> > > > @@ -389,6 +473,11 @@ static int evm_protect_xattr(struct
> > > user_namespace *mnt_userns,
> > > >  	if (evm_status == INTEGRITY_FAIL_IMMUTABLE)
> > > >  		return 0;
> > > >
> > > > +	if (evm_status == INTEGRITY_PASS_IMMUTABLE &&
> > > > +	    !evm_xattr_change(mnt_userns, dentry, xattr_name, xattr_value,
> > > > +			      xattr_value_len))
> > > > +		return 0;
> > > > +
> > >
> > > If the purpose of evm_protect_xattr() is to prevent allowing an invalid
> > > security.evm xattr from being re-calculated and updated, making it
> > > valid, INTEGRITY_PASS_IMMUTABLE shouldn't need to be conditional.
> Any
> > > time there is an attr or xattr change, including setting it to the
> > > existing value, the status flag should be reset.
> > >
> > > I'm wondering if making INTEGRITY_PASS_IMMUTABLE conditional would
> > > prevent the file from being resigned.
> > >
> > > >  	if (evm_status != INTEGRITY_PASS)
> > > >  		integrity_audit_msg(AUDIT_INTEGRITY_METADATA,
> > > d_backing_inode(dentry),
> > > >  				    dentry->d_name.name,
> > > "appraise_metadata",
> > >
> > > This would then be updated to if not INTEGRITY_PASS or
> > > INTEGRITY_PASS_IMMUTABLE.  The subsequent "return" would need to
> be
> > > updated as well.
> >
> > I agree on the first suggestion, to reduce the number of log messages.
> > For the second, if you meant that we should return 0 if the status is
> > INTEGRITY_PASS_IMMUTABLE, I thought we wanted to deny xattr
> > changes when there is an EVM portable signature.
> 
> Why?  I must be missing something.  As long as we're not relying on the
> cached status, allowing the file metadata to be updated shouldn't be an
> issue.

We may want to prevent accidental changes, for example.

Roberto

HUAWEI TECHNOLOGIES Duesseldorf GmbH, HRB 56063
Managing Director: Li Peng, Li Jian, Shi Yanli

  reply index

Thread overview: 40+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-04-07 10:52 [PATCH v5 00/12] evm: Improve usability of portable signatures Roberto Sassu
2021-04-07 10:52 ` [PATCH v5 01/12] evm: Execute evm_inode_init_security() only when an HMAC key is loaded Roberto Sassu
2021-04-07 10:52 ` [PATCH v5 02/12] evm: Load EVM key in ima_load_x509() to avoid appraisal Roberto Sassu
2021-04-07 10:52 ` [PATCH v5 03/12] evm: Refuse EVM_ALLOW_METADATA_WRITES only if an HMAC key is loaded Roberto Sassu
2021-04-30 20:28   ` Mimi Zohar
2021-04-07 10:52 ` [PATCH v5 04/12] ima: Move ima_reset_appraise_flags() call to post hooks Roberto Sassu
2021-04-07 16:17   ` Casey Schaufler
2021-04-07 16:31     ` Roberto Sassu
2021-04-26 19:49     ` Mimi Zohar
2021-04-07 10:52 ` [PATCH v5 05/12] evm: Introduce evm_status_revalidate() Roberto Sassu
2021-04-07 10:52 ` [PATCH v5 06/12] evm: Ignore INTEGRITY_NOLABEL/INTEGRITY_NOXATTRS if conditions are safe Roberto Sassu
2021-05-03  0:12   ` Mimi Zohar
2021-05-03  7:55     ` Roberto Sassu
2021-05-03 12:07       ` Mimi Zohar
2021-05-03 14:15       ` Roberto Sassu
2021-05-03 14:34         ` Mimi Zohar
2021-05-04 13:16           ` Roberto Sassu
2021-05-04 13:45             ` Mimi Zohar
2021-04-07 10:52 ` [PATCH v5 07/12] evm: Allow xattr/attr operations for portable signatures Roberto Sassu
2021-05-03  0:12   ` Mimi Zohar
2021-05-04 14:28     ` Roberto Sassu
2021-05-04 14:49       ` Mimi Zohar
2021-04-07 10:52 ` [PATCH v5 08/12] evm: Pass user namespace to set/remove xattr hooks Roberto Sassu
2021-04-07 12:06   ` Christian Brauner
2021-04-07 10:52 ` [PATCH v5 09/12] evm: Allow setxattr() and setattr() for unmodified metadata Roberto Sassu
2021-04-07 12:05   ` Christian Brauner
2021-04-07 15:23   ` kernel test robot
2021-04-07 18:14   ` kernel test robot
2021-04-07 19:28     ` [RESEND][PATCH " Roberto Sassu
2021-05-03 13:00   ` [PATCH " Mimi Zohar
2021-05-03 14:48     ` Roberto Sassu
2021-05-03 15:13       ` Mimi Zohar
2021-05-03 15:30         ` Roberto Sassu
2021-05-03 15:11     ` Roberto Sassu
2021-05-03 15:26       ` Mimi Zohar
2021-05-03 15:32         ` Roberto Sassu [this message]
2021-05-03 15:48           ` Mimi Zohar
2021-04-07 10:52 ` [PATCH v5 10/12] ima: Allow imasig requirement to be satisfied by EVM portable signatures Roberto Sassu
2021-04-07 10:52 ` [PATCH v5 11/12] ima: Introduce template field evmsig and write to field sig as fallback Roberto Sassu
2021-04-07 10:52 ` [PATCH v5 12/12] ima: Don't remove security.ima if file must not be appraised Roberto Sassu

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