Re: [PATCH v2 1/4] misc: fastrpc: Add NULL check to fastrpc_buf_free to prevent crash

[Bjorn Andersson]

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@xxxxxxxxxxxxxxxx>
> > > > > 
> > > > > 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@xxxxxxxxxxxxxxxx/
> > 
> > > 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@xxxxxxxxxxxxxxxx/
> > 
> > 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

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