linux-kernel - Re: [PATCH] kernfs: fix potential null-ptr-deref in kernfs_path_from_node

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Message-ID: <1902f7d9-2dcf-acf4-44d6-8c26ff48ea6d@huawei.com>
Date:   Mon, 28 Nov 2022 09:15:23 +0800
From:   "Leizhen (ThunderTown)" <thunder.leizhen@...wei.com>
To:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>
CC:     Tejun Heo <tj@...nel.org>, <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] kernfs: fix potential null-ptr-deref in
 kernfs_path_from_node_locked()



On 2022/11/26 18:25, Greg Kroah-Hartman wrote:
> On Sat, Nov 26, 2022 at 05:49:50PM +0800, Leizhen (ThunderTown) wrote:
>>
>>
>> On 2022/11/24 10:52, Leizhen (ThunderTown) wrote:
>>>
>>>
>>> On 2022/11/24 10:28, Leizhen (ThunderTown) wrote:
>>>>
>>>>
>>>> On 2022/11/24 10:24, Leizhen (ThunderTown) wrote:
>>>>>
>>>>>
>>>>> On 2022/11/24 0:55, Tejun Heo wrote:
>>>>>> On Wed, Nov 23, 2022 at 10:04:19AM +0800, Zhen Lei wrote:
>>>>>>> Ensure that the 'buf' is not empty before strlcpy() uses it.
>>>>>>>
>>>>>>> Commit bbe70e4e4211 ("fs: kernfs: Fix possible null-pointer dereferences
>>>>>>> in kernfs_path_from_node_locked()") first noticed this, but it didn't
>>>>>>> fix it completely.
>>>>>>>
>>>>>>> Fixes: 9f6df573a404 ("kernfs: Add API to generate relative kernfs path")
>>>>>>> Signed-off-by: Zhen Lei <thunder.leizhen@...wei.com>
>>>>>>
>>>>>> I think the right thing to do is removing that if. It makes no sense to call
>>>>>> that function with NULL buf and the fact that nobody reported crashes on
>>>>>> NULL buf indicates that we in fact never do.
>>
>> kernfs_path_from_node
>>     -->kernfs_path_from_node_locked
>>
>> EXPORT_SYMBOL_GPL(kernfs_path_from_node)
>>
>> I've rethought it. The export APIs need to do null pointer check, right?
> 
> No, callers should get this right.  Are there any in-tree ones that do
> not?

Thanks. I got it.

> 
> thanks,
> 
> greg k-h
> .
> 

-- 
Regards,
  Zhen Lei