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

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Date:   Thu, 28 May 2020 18:37:12 +0200
From:   Takashi Iwai <tiwai@...e.de>
To:     Roberto Sassu <roberto.sassu@...wei.com>
Cc:     linux-integrity@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: Oops at boot with linux-next kernel with IMA boot options

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...

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;