linux-kernel - Re: [PATCH v2 1/4] misc: fastrpc: Add NULL check to fastrpc_buf

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Message-ID: <fac9526e-a184-4c4d-9d29-b37400bf47fe@oss.qualcomm.com>
Date: Thu, 5 Feb 2026 17:07:03 +0800
From: Jianping <jianping.li@....qualcomm.com>
To: Bjorn Andersson <andersson@...nel.org>
Cc: Greg KH <gregkh@...uxfoundation.org>, srini@...nel.org,
        amahesh@....qualcomm.com, arnd@...db.de, linux-arm-msm@...r.kernel.org,
        Ekansh Gupta <ekansh.gupta@....qualcomm.com>,
        thierry.escande@...aro.org, abelvesa@...nel.org,
        dri-devel@...ts.freedesktop.org, linux-kernel@...r.kernel.org,
        quic_chennak@...cinc.com, stable@...nel.org
Subject: Re: [PATCH v2 1/4] misc: fastrpc: Add NULL check to fastrpc_buf_free
 to prevent crash



On 2/4/2026 5:32 AM, Bjorn Andersson wrote:
> On Tue, Feb 03, 2026 at 08:08:16PM +0800, Jianping wrote:
>>
>>
>> On 2/2/2026 4:41 PM, Greg KH wrote:
>>> On Mon, Feb 02, 2026 at 03:13:10PM +0800, Jianping wrote:
>>>>
>>>>
>>>> On 1/16/2026 10:49 PM, Greg KH wrote:
>>>>> On Thu, Jan 15, 2026 at 04:28:48PM +0800, Jianping Li wrote:
>>>>>> From: Ekansh Gupta <ekansh.gupta@....qualcomm.com>
>>>>>>
>>>>>> The fastrpc_buf_free function currently does not handle the case where
>>>>>> the input buffer pointer (buf) is NULL. This can lead to a null pointer
>>>>>> dereference, causing a crash or undefined behavior when the function
>>>>>> attempts to access members of the buf structure. Add a NULL check to
>>>>>> ensure safe handling of NULL pointers and prevent potential crashes.
>>>>>
>>>>> What caller passes in NULL here?  I did a quick look, and see where the
>>>>> callers check this properly if it could be NULL, otherwise it all looks
>>>>> sane to me.  What in-kernel user is causing a crash here?  Why not fix
>>>>> the caller up instead?
>>>>>
>>>>> thanks,
>>>>>
>>>>> greg k-h
>>>>
>>>> It's a saftety coding: to eliminate NULL checks on the caller side, as we do
>>>> in a lot of other kernel API.
>>>
>>> But you do not do that for all functions in the kernel, otherwise the
>>> kernel would be full of checks that are never hit at all.
>> To clarify the intention: this change was not triggered by any real crash in
>> current callers. The motivation came from the v1 review discussion [1],
>> where it was suggested that a NULL check in fastrpc_buf_free() would allow
>> simplifying some of the caller paths.
>>
>> [1] https://lore.kernel.org/all/c80c48a1-f1b6-4520-9d7c-3a83915c7717@oss.qualcomm.com/
>>>
>>>> And it was pointed out in the v1 patch discussion that this change was
>>>> needed:
>>>> https://lore.kernel.org/all/c80c48a1-f1b6-4520-9d7c-3a83915c7717@oss.qualcomm.com/
>>>
>>> Were the checks removed from the caller side like was asked for?
>>
>> Currently, I have placed the check inside the API and removed all the checks
>> outside the API.
>>
>>>
>>> Also, your changelog makes it sound like this is a real bugfix for
>>> something, when it is not at all, which is what I object to the most.
>>> Don't make scary changelogs for things that are not actually happening.
>>
>> You are correct. I will modify the commit text that caused the
>> misunderstanding.
>>
> 
> You should then also drop Cc: stable and Fixes:, as this is no longer a
> bug fix. And make sure you don't put actual bug fixes after this one in
> the series (i.e. it probably shouldn't be patch 1/4).
> 
> Regards,
> Bjorn

Thank Bjorn for the reminder, I will adjust the order of my patch.

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