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

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Date:   Tue, 31 Jan 2023 18:16:13 +0100
From:   Martin Kaiser <martin@...ser.cx>
To:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Cc:     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

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")

Best regards,

   Martin