linux-kernel - Re: [PATCH] staging: r8188eu: fix NULL check for rcu pointer

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Date:   Wed, 1 Feb 2023 08:06:31 +0300
From:   Dan Carpenter <error27@...il.com>
To:     Martin Kaiser <martin@...ser.cx>
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Larry Finger <Larry.Finger@...inger.net>,
        Phillip Potter <phil@...lpotter.co.uk>,
        Michael Straube <straube.linux@...il.com>,
        Pavel Skripkin <paskripkin@...il.com>,
        linux-staging@...ts.linux.dev, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] staging: r8188eu: fix NULL check for rcu pointer

On Tue, Jan 31, 2023 at 06:16:13PM +0100, Martin Kaiser wrote:
> Hello Greg and all,
> 
> Thus wrote Greg Kroah-Hartman (gregkh@...uxfoundation.org):
> 
> > On Tue, Jan 31, 2023 at 10:00:57AM +0100, Martin Kaiser wrote:
> > > Fix the NULL check for padapter->pnetdev->rx_handler_data.
> 
> > > The current code calls rcu_dereference while it holds the rcu read lock
> > > and checks the pointer after releasing the lock. An rcu pointer may only be
> > > used between calls to rcu_read_lock and rcu_read_unlock.
> 
> > > Replace the check with rcu_access_pointer. My understanding is that this
> > > function returns the value of the pointer and needs no locking. We can
> > > then check the pointer but we must not dereference it.
> 
> > > Signed-off-by: Martin Kaiser <martin@...ser.cx>
> 
> > What commit id does this fix?
> 
> the code that checks br_port has been around since the driver was
> imported into staging.
> 
> If the patch is considered as a fix, it should have
> 
> Fixes: 15865124feed ("staging: r8188eu: introduce new core dir for RTL8188eu driver")

I don't think it is a fix as we discuss later in the thread.

But if it were then it's still really useful to record that.  I normally
don't record when Fixes are from before the git era because one time,
ten years ago, one person said not to do that.  But really even there I
personally think Fixes: 1da177e4c3f4 ("Linux-2.6.12-rc2") is useful.

It tells the tools how far to backport things.  It tells us if most of
our bugs come from the very start or if we're introducing them later.

regards,
dan carpenter