[PATCH] ima: fix infinite loop within "ima_match_policy" function.

[Mimi Zohar]

On Thu, 2021-08-19 at 12:58 +0000, THOBY Simon wrote:
> Hi Liqiong,
> 
> On 8/19/21 12:15 PM, liqiong wrote:
> > When "ima_match_policy" is looping while "ima_update_policy" changs
> > the variable "ima_rules", then "ima_match_policy" may can't exit loop,
> > and kernel keeps printf "rcu_sched detected stall on CPU ...".
> > 
> > It occurs at boot phase, systemd-services are being checked within
> > "ima_match_policy,at the same time, the variable "ima_rules"
> > is changed by a service.
> 
> First off, thanks for finding and identifying this nasty bug.

Once the initial builtin policy rules have been replaced by a custom
policy, rules may only be appended by splicing the new rules with the
existing rules.  There should never be a problem reading the rules at
that point.   Does this problem occur before the builtin policy rules
have been replaced with a custom policy?

Mimi