linux-kernel - Re: [PATCH 1/2] iscsi_tcp: Fix NULL pointer dereference in iscsi_sw_tcp_conn_get

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Date:   Mon, 7 Mar 2022 19:55:56 +0800
From:   Wenchao Hao <haowenchao@...wei.com>
To:     Mike Christie <michael.christie@...cle.com>,
        Lee Duncan <lduncan@...e.com>, Chris Leech <cleech@...hat.com>,
        "James E . J . Bottomley" <jejb@...ux.ibm.com>,
        "Martin K . Petersen" <martin.petersen@...cle.com>,
        <open-iscsi@...glegroups.com>, <linux-scsi@...r.kernel.org>,
        <linux-kernel@...r.kernel.org>
CC:     Wu Bo <wubo40@...wei.com>, Zhiqiang Liu <liuzhiqiang26@...wei.com>,
        <linfeilong@...wei.com>
Subject: Re: [PATCH 1/2] iscsi_tcp: Fix NULL pointer dereference in
 iscsi_sw_tcp_conn_get_param()

On 2022/3/3 23:03, Mike Christie wrote:
> On 3/3/22 8:56 PM, Wenchao Hao wrote:
>> kernel might crash in iscsi_sw_tcp_conn_get_param() because it dereference
>> an invalid address.
>>
>> The initialization of iscsi_conn's dd_data is after device_register() of
>> struct iscsi_cls_conn, so iscsi_conn's dd_data might not initialized when
>> iscsi_sw_tcp_conn_get_param() is called.
>>
> 
> We are actually doing sysfs/device addition wrong.
> 
> We should be doing the 2 step setup where in step 1 we alloc/init.
> When everything is allocated and initialized, then we should do
> device_add which exposes us to sysfs. On the teardown side, we are
> then supposed to do 2 steps where the remove function does device_del
> which waits until sysfs accesses are completed. We can then tear
> the structs down and free them and call device_put.
> 

I reviewed the teardown flow of iscsi_cls_conn, it has already written 
as what you saied.


> The exposure to NL would be similar where it goes into the wrapper
> around device_add. However, see my comments on the other patch where
> I don't think we can hit the bug you mention because every nl cmd
> that calls into the drivers is done under the rx_queue_mutex.
> 
> I think we should separate the iscsi_create_conn function like we
> do for sessions. This is going to be a little more involved because
> you need to also convert iscsi_tcp_conn_setup and the drivers since
> we can call into the drivers for the get_conn_param callout.
> .
> 

I hesitated about when should we call device_add(). I think there are 
two places to call it.

The first one is in iscsi_conn_setup(), after some initialization of 
conn, it keeps same with previous's implement and need not to change 
drivers' code. What's more, the change can fix iscsi_tcp's NULL pointer 
access.  While this change can not make sure the LLDs related sources 
are already initialized when iscsi_cls_conn is exposed to sysfs. It 
means LLDs' callback are still responsible to check if the resources are 
accessible.

Another one is in create_conn callback for each driver's 
iscsi_transport.  This need us to change each driver's code.

I send 2 patches which make changes in iscsi_conn_setup(), it's ok with 
iscsi_tcp, would you help to review them?