linux-kernel - Re: [PATCH v4 2/2] IMA: Call workqueue functions to measure queued keys

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Message-ID: <95606a84-ea7d-dda2-5ced-7418fe802ecf@linux.microsoft.com>
Date:   Tue, 17 Dec 2019 19:00:10 -0800
From:   Lakshmi Ramasubramanian <nramas@...ux.microsoft.com>
To:     James Bottomley <James.Bottomley@...senPartnership.com>,
        zohar@...ux.ibm.com, linux-integrity@...r.kernel.org
Cc:     eric.snowberg@...cle.com, dhowells@...hat.com,
        mathew.j.martineau@...ux.intel.com, matthewgarrett@...gle.com,
        sashal@...nel.org, jamorris@...ux.microsoft.com,
        linux-kernel@...r.kernel.org, keyrings@...r.kernel.org
Subject: Re: [PATCH v4 2/2] IMA: Call workqueue functions to measure queued
 keys

On 12/17/2019 6:44 PM, Lakshmi Ramasubramanian wrote:

>>
>> The direct implication of the comment and the lock dance with the
>> temporary list and the processed flag is that stuff can be added to the
>> ima_keys list after you drop the mutex.  Your explanation in the prior
>> couple of emails says that nothing can be added because the
>> ima_process_keys flag setting prevents it.  If the latter is true, you
>> can simply drop the lock after setting the flag and rely on ima_keys
>> not changing to run it through process_buffer_measurement without
>> needing any of the intermediate list or the processed flag.  If the
>> latter isn't true then any key added to ima_keys after the mutex is
>> dropped is never processed.
>>
>> James

One more scenario needs to be taken care - that still doesn't require a 
temp list, but will need a local flag.

Say, two threads race to call ima_process_queued_keys().
Both find ima_process_keys flag is false.
They now race to take to the lock.
Only the 1st one setting the flag to true should process queued keys.

  -lakshmi