linux-kernel - Re: [PATCH] tpm: fix a race between poll and write in tpm-dev-common

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Date:   Tue, 19 Mar 2019 12:09:35 -0700
From:   Tadeusz Struk <tadeusz.struk@...el.com>
To:     James Bottomley <James.Bottomley@...senPartnership.com>,
        jarkko.sakkinen@...ux.intel.com
Cc:     grawity@...il.com, linux-integrity@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] tpm: fix a race between poll and write in tpm-dev-common

On 3/18/19 4:19 PM, James Bottomley wrote:
>> @@ -203,12 +203,14 @@ __poll_t tpm_common_poll(struct file *file,
>> poll_table *wait)
>>  	__poll_t mask = 0;
>>  
>>  	poll_wait(file, &priv->async_wait, wait);
>> +	mutex_lock(&priv->buffer_mutex);
>>  
>>  	if (!priv->response_read || priv->response_length)
>>  		mask = EPOLLIN | EPOLLRDNORM;
>>  	else
>>  		mask = EPOLLOUT | EPOLLWRNORM;
>>  
>> +	mutex_unlock(&priv->buffer_mutex);
> This doesn't do anything to address the theory that the queued work
> hasn't run before the poll wakes up, does it?  If you have an
> alternative theory, could you explain it?

Right, it needs to be guarded by the mutex and also the condition
should only check priv->response_length, because we only care
about if there is data to read. The response_read flag only
prevents double writes, without reading in the middle (or a timeout)
which clean it. I will send a v2 soon.

Thanks,
-- 
Tadeusz