Whitelisting with IMA

Whitelisting with IMA

[m3hm00d]

tldr: Is there some way to ask IMA not to open (execute) unknown binaries

Hi all,

I saw some comments on RFC for WhiteEgret LSM. Someone on the same
thread said that IMA could be used for whitelisting as well. Based on
a couple of hours with IMA, it seems to me that IMA can only stop
execution of (altered) binaries whose hash/sign was earlier measured.

If a user installs a new (unknown) application, it seems like IMA is
going to allow that application to run since IMA can't find any
integrity loss since IMA doesn't have any 'good' value against the new
application. Is this correct? Or is there some other option to ask IMA
not to execute any unknown binary?

Kind regards,
m3hm00d

Re: Whitelisting with IMA

[Roberto Sassu]

On 5/12/2019 11:37 AM, m3hm00d wrote:
> tldr: Is there some way to ask IMA not to open (execute) unknown binaries
> 
> Hi all,
> 
> I saw some comments on RFC for WhiteEgret LSM. Someone on the same
> thread said that IMA could be used for whitelisting as well. Based on
> a couple of hours with IMA, it seems to me that IMA can only stop
> execution of (altered) binaries whose hash/sign was earlier measured.

Hi

I'm developing an extension (IMA Digest Lists) to allow access to files
depending on a white list (for example digests in RPM headers). I will
publish a new version soon. For the concept, please have a look at:

https://github.com/euleros/linux/wiki/IMA-Digest-Lists-Extension
https://github.com/euleros/digest-list-tools/wiki/Architecture


> If a user installs a new (unknown) application, it seems like IMA is
> going to allow that application to run since IMA can't find any
> integrity loss since IMA doesn't have any 'good' value against the new
> application. Is this correct? Or is there some other option to ask IMA
> not to execute any unknown binary?

If appraisal is enabled, and the application has no signature/HMAC,
access would be denied. If the application is installed by a package
manager, probably files will have a HMAC and access would be granted
unless the IMA policy requires signatures.

Roberto


> Kind regards,
> m3hm00d
> 

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Re: Whitelisting with IMA

[m3hm00d]

On Mon, May 13, 2019 at 9:09 AM Roberto Sassu <roberto.sassu@huawei.com> wrote:
>
> On 5/12/2019 11:37 AM, m3hm00d wrote:
> > tldr: Is there some way to ask IMA not to open (execute) unknown binaries
> >
> > Hi all,
> >
> > I saw some comments on RFC for WhiteEgret LSM. Someone on the same
> > thread said that IMA could be used for whitelisting as well. Based on
> > a couple of hours with IMA, it seems to me that IMA can only stop
> > execution of (altered) binaries whose hash/sign was earlier measured.
>
> Hi
>
> I'm developing an extension (IMA Digest Lists) to allow access to files
> depending on a white list (for example digests in RPM headers). I will
> publish a new version soon. For the concept, please have a look at:
>
> https://github.com/euleros/linux/wiki/IMA-Digest-Lists-Extension
> https://github.com/euleros/digest-list-tools/wiki/Architecture
>

Hi there,

Interesting idea. Will definitely look it over.

> > If a user installs a new (unknown) application, it seems like IMA is
> > going to allow that application to run since IMA can't find any
> > integrity loss since IMA doesn't have any 'good' value against the new
> > application. Is this correct? Or is there some other option to ask IMA
> > not to execute any unknown binary?
>
> If appraisal is enabled, and the application has no signature/HMAC,
> access would be denied. If the application is installed by a package
> manager, probably files will have a HMAC and access would be granted
> unless the IMA policy requires signatures.
>

Turns out I was passing `ima_policy=tcb` to kernel. That's (probably)
why no appraisal was happening and even new (unknown) scripts kept
running. After some reading, I changed it to `ima_policy=appraise_tcb`
but the system won't allow me to login now (error saying 'Incorrect
login' or something like that). The best sources of info on IMA for me
were gentoo wiki and project page on soureforge. Could you please
guide me to a more thorough documentation meant for
users/administrators and other people wanting to learn more about
IMA/EVM?


> Roberto

Kind regards,
m3hm00d