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From: Mimi Zohar <>
To: THOBY Simon <>,
	"" <>,
	BARVAUX Didier <>
Subject: Re: [PATCH v4 5/5] IMA: introduce a new policy option func=SETXATTR_CHECK
Date: Tue, 27 Jul 2021 13:25:16 -0400	[thread overview]
Message-ID: <> (raw)
In-Reply-To: <>

Hi Simon,

On Tue, 2021-07-27 at 16:33 +0000, THOBY Simon wrote:
> While users can restrict the accepted hash algorithms for the
> security.ima xattr file signature when appraising said file, users
> cannot restrict the algorithms that can be set on that attribute:
> any algorithm built in the kernel is accepted on a write.
> Define a new value for the ima policy option 'func' that restricts
> globally the hash algorithms accepted when writing the security.ima
> xattr.
> When a policy contains a rule of the form
> 	appraise func=SETXATTR_CHECK appraise_hash=sha256,sha384,sha512
> only values corresponding to one of these three digest algorithms
> will be accepted for writing the security.ima xattr.
> Attempting to write the attribute using another algorithm (or "free-form"
> data) will be denied with an audit log message.
> In the absence of such a policy rule, the default is still to only
> accept hash algorithms built in the kernel (with all the limitations
> that entails).
> On policy update, the latest SETXATTR_CHECK rule is the only one
> that apply, and other SETXATTR_CHECK rules are deleted.
> Signed-off-by: Simon Thoby <>

Sorry, I was just getting to this patch, when you re-posted the patch
set.  In the future, I'll make sure the responses are sent in quick

There are a number of assumptions related to the IMA policy:
- A builtin policy may be replaced by a custom policy.
- Depending on the Kconfig, the policy rules may not change be updated.
- Subsequent to replacing the builtin policy with a custom policy,
rules may only be appended, based on the Kconfig.

The locking around the policy rules is dependent on these assumptions. 
Removing policy rules is a major change that needs to be considered
carefully.  Why should "func=SETXATTR_CHECK"  be treated any
differently than any other policy rule?  How would an attestation
server know which setxattr rule was enabled at the time the file was



  reply	other threads:[~2021-07-27 17:25 UTC|newest]

Thread overview: 17+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-07-27 16:33 [PATCH v4 0/5] IMA: restrict the accepted digest algorithms for THOBY Simon
2021-07-27 16:33 ` [PATCH v4 1/5] IMA: remove the dependency on CRYPTO_MD5 THOBY Simon
2021-07-27 17:57   ` Mimi Zohar
2021-07-27 16:33 ` [PATCH v4 2/5] IMA: block writes of the security.ima xattr with unsupported algorithms THOBY Simon
2021-07-27 20:32   ` Mimi Zohar
2021-07-28  7:00     ` THOBY Simon
2021-07-28 12:43       ` Mimi Zohar
2021-07-28 12:53         ` THOBY Simon
2021-07-28 13:09           ` Mimi Zohar
2021-07-27 16:33 ` [PATCH v4 3/5] IMA: add support to restrict the hash algorithms used for file appraisal THOBY Simon
2021-07-27 20:38   ` Mimi Zohar
2021-07-27 16:33 ` [PATCH v4 4/5] IMA: add a policy option to restrict xattr hash algorithms on appraisal THOBY Simon
2021-07-27 21:07   ` Mimi Zohar
2021-07-27 16:33 ` [PATCH v4 5/5] IMA: introduce a new policy option func=SETXATTR_CHECK THOBY Simon
2021-07-27 17:25   ` Mimi Zohar [this message]
2021-07-27 17:58     ` THOBY Simon
2021-07-27 17:47 ` [PATCH v4 0/5] IMA: restrict the accepted digest algorithms for Mimi Zohar

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