linux-kernel - Re: [PATCH] ima: fix deadlock when traversing "ima_default

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Date:   Fri, 27 Aug 2021 12:16:06 -0400
From:   Mimi Zohar <zohar@...ux.ibm.com>
To:     liqiong <liqiong@...china.com>, Simon.THOBY@...eris.fr
Cc:     dmitry.kasatkin@...il.com, jmorris@...ei.org, serge@...lyn.com,
        linux-integrity@...r.kernel.org,
        linux-security-module@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] ima: fix deadlock when traversing "ima_default_rules".

On Fri, 2021-08-27 at 18:35 +0800, liqiong wrote:
> The current IMA ruleset is identified by the variable "ima_rules"
> that default to "&ima_default_rules". When loading a custom policy
> for the first time, the variable is updated to "&ima_policy_rules"
> instead. That update isn't RCU-safe, and deadlocks are possible.
> Indeed, some functions like ima_match_policy() may loop indefinitely
> when traversing "ima_default_rules" with list_for_each_entry_rcu().
> 
> When iterating over the default ruleset back to head, if the list
> head is "ima_default_rules", and "ima_rules" have been updated to
> "&ima_policy_rules", the loop condition (&entry->list != ima_rules)
> stays always true, traversing won't terminate, causing a soft lockup
> and RCU stalls.
> 
> Introduce a temporary value for "ima_rules" when iterating over
> the ruleset to avoid the deadlocks.
> 
> Signed-off-by: liqiong <liqiong@...china.com>
> Reviewed-by: THOBY Simon <Simon.THOBY@...eris.fr>

Thank you, Liqiong, Simon.   This patch set is now queued in the next-
integrity-testing 
branch.

Mimi