From: Mimi Zohar <zohar@linux.ibm.com>
To: Roberto Sassu <roberto.sassu@huawei.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, 03 May 2021 11:48:04 -0400 [thread overview]
Message-ID: <d48e3595d0a39cc0ac82519c1c444eeacc8b8c58.camel@linux.ibm.com> (raw)
In-Reply-To: <b0bfaf2352b045dfaf443ae3af73b60e@huawei.com>
On Mon, 2021-05-03 at 15:32 +0000, Roberto Sassu wrote:
> > 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.
Let's keep it simple, getting the basics working properly first. Then
we can decide if this is something that we really want/need to defend
against.
thanks,
Mimi
next prev parent reply other threads:[~2021-05-03 15:48 UTC|newest]
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
2021-05-03 15:48 ` Mimi Zohar [this message]
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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