linux-kernel - Re: [PATCH] ima: fix deadlock within RCU list of ima

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Date:   Thu, 26 Aug 2021 16:15:49 +0800
From:   liqiong <liqiong@...china.com>
To:     THOBY Simon <Simon.THOBY@...eris.fr>,
        Mimi Zohar <zohar@...ux.ibm.com>
Cc:     "dmitry.kasatkin@...il.com" <dmitry.kasatkin@...il.com>,
        "jmorris@...ei.org" <jmorris@...ei.org>,
        "serge@...lyn.com" <serge@...lyn.com>,
        "linux-integrity@...r.kernel.org" <linux-integrity@...r.kernel.org>,
        "linux-security-module@...r.kernel.org" 
        <linux-security-module@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] ima: fix deadlock within RCU list of ima_rules

Hi Simon,

Thanks for your help, your advice is clear, can i just use it,
how about this:


The current IMA ruleset is identified by the variable "ima_rules",
and the pointer starts pointing at the list "ima_default_rules".
When loading a custom policy for the first time, the variable is
updated to point to the list "ima_policy_rules" instead. That update
isn't RCU-safe, and deadlocks are possible.

Introduce a temporary value for "ima_rules" when iterating over
the ruleset to avoid the deadlocks.


Signed-off-by: liqiong <liqiong@...china.com>
---
 security/integrity/ima/ima_policy.c | 17 ++++++++++++-----
 1 file changed, 12 insertions(+), 5 deletions(-)

diff --git a/security/integrity/ima/ima_policy.c b/security/integrity/ima/ima_policy.c
index fd5d46e511f1..e92b197bfd3c 100644
--- a/security/integrity/ima/ima_policy.c
+++ b/security/integrity/ima/ima_policy.c



Thanks

liqiong

在 2021年08月25日 20:03, THOBY Simon 写道:
> Hi Liqiong,
>
> On 8/25/21 1:45 PM, liqiong wrote:
>> Hi Mimi,
>>
>> This copy may be better.
>>
>>
>> subject: ima: fix deadlock when iterating over the init "ima_rules" list.
>>
>>
> As Mimi said, consider adding an introducing paragraph, like:
> 'The current IMA ruleset is identified by the variable "ima_rules",
> and the pointer starts pointing at the list "ima_default_rules". When
> loading a custom policy for the first time, the variable is
> updated to point to the list "ima_policy_rules" instead. That update
> isn't RCU-safe, and deadlocks are possible.'
>
>> When traversing back to head, the init "ima_rules" list can't exit
>> iterating if "ima_rules" has been updated to "ima_policy_rules".
>> It causes soft lockup and RCU stalls. So we can introduce a duplicate
>> of "ima_rules" for each "ima_rules" list loop.
> Per the process (see 'Documentation/process/submitting-patches.rst'),
> please prefer an imperative style (written in another paragraph):
> 'Introduce a temporary value for "ima_rules" when iterating over the ruleset.'
>
>
> Thanks,
> Simon