RE: Oops at boot with linux-next kernel with IMA boot options

Roberto Sassu
2020-05-28T17:37:03Z

> From: linux-integrity-owner@vger.kernel.org [mailto:linux-integrity-
> owner@vger.kernel.org] On Behalf Of Takashi Iwai
> On Thu, 28 May 2020 17:35:16 +0200,
> Takashi Iwai wrote:
> >
> > Hi Roberto,
> >
> > it seems that the recent changes in IMA in linux-next caused a
> > regression: namely it triggers an Oops when booting with the options
> > ima_policy=tcb ima_template_fmt='d-ng|n-ng|d|ng'
>
> And further experiment revealed that passing only ima_template_fmt=d
> is enough for triggering the bug. Other formats don't matter.
>
> (snip)
> > It's a KVM instance without any TPM stuff, just passed the options
> > above. I could trigger the same bug on a bare metal, too.
> >
> > Then I performed bisection and it spotted the commit:
> > 6f1a1d103b48b1533a9c804e7a069e2c8e937ce7
> > ima: Switch to ima_hash_algo for boot aggregate
> >
> > Actually reverting this commit fixed the Oops again.
>
> So, looking at the fact above (triggered by "d") and this bisection
> result, it seems that the issue is specific to ima_eventdigest_init().
> The difference from others is that this has a check by
> ima_template_hash_algo_allowed(), and currently the check allows only
> SHA1 and MD5, while now SHA256 is assigned as default. So I tested
> adding SHA256 there like below, and it seems working.
>
> Hopefully I'm heading to a right direction...

Hi Takashi

boot_aggregate is the only entry for which there is no file descriptor.
The file descriptor is used to recalculate the digest if it is not SHA1
or MD5. For boot_aggregate, we should use instead
ima_calc_boot_aggregate(). I will provide a patch.

I see that the .file member of event_data in
ima_add_boot_aggregate() is not initialized. Can you please try
to set .file to NULL?

Thanks

Roberto

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

> thanks,
>
> Takashi
>
> --- a/security/integrity/ima/ima_template_lib.c
> +++ b/security/integrity/ima/ima_template_lib.c
> @@ -13,7 +13,8 @@
>
> static bool ima_template_hash_algo_allowed(u8 algo)
> {
> - if (algo == HASH_ALGO_SHA1 || algo == HASH_ALGO_MD5)
> + if (algo == HASH_ALGO_SHA1 || algo == HASH_ALGO_SHA256 ||
> + algo == HASH_ALGO_MD5)
> return true;
>
> return false;