linux-kernel - Re: [PATCH] net: bluetooth: Fix null pointer dereference in hci_event

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Date:   Thu, 10 Sep 2020 11:32:08 +0530
From:   Anmol Karn <anmol.karan123@...il.com>
To:     Eric Biggers <ebiggers@...nel.org>
Cc:     marcel@...tmann.org, johan.hedberg@...il.com,
        linux-kernel-mentees@...ts.linuxfoundation.org,
        linux-kernel@...r.kernel.org, syzkaller-bugs@...glegroups.com,
        netdev@...r.kernel.org, linux-bluetooth@...r.kernel.org,
        kuba@...nel.org, davem@...emloft.net,
        syzbot+0bef568258653cff272f@...kaller.appspotmail.com
Subject: Re: [PATCH] net: bluetooth: Fix null pointer dereference in
 hci_event_packet()

On Wed, Sep 09, 2020 at 10:06:59PM -0700, Eric Biggers wrote:
> On Thu, Sep 10, 2020 at 10:04:24AM +0530, Anmol Karn wrote:
> > Prevent hci_phy_link_complete_evt() from dereferencing 'hcon->amp_mgr'
> > as NULL. Fix it by adding pointer check for it.
> > 
> > Reported-and-tested-by: syzbot+0bef568258653cff272f@...kaller.appspotmail.com
> > Link: https://syzkaller.appspot.com/bug?extid=0bef568258653cff272f
> > Signed-off-by: Anmol Karn <anmol.karan123@...il.com>
> > ---
> >  net/bluetooth/hci_event.c | 5 +++++
> >  1 file changed, 5 insertions(+)
> > 
> > diff --git a/net/bluetooth/hci_event.c b/net/bluetooth/hci_event.c
> > index 4b7fc430793c..871e16804433 100644
> > --- a/net/bluetooth/hci_event.c
> > +++ b/net/bluetooth/hci_event.c
> > @@ -4936,6 +4936,11 @@ static void hci_phy_link_complete_evt(struct hci_dev *hdev,
> >  		return;
> >  	}
> >  
> > +	if (IS_ERR_OR_NULL(hcon->amp_mgr)) {
> > +		hci_dev_unlock(hdev);
> > +		return;
> > +	}
> > +
> 

Hello Sir,

> In patches that fix a NULL pointer dereference, please include a brief
> explanation of why the pointer can be NULL, including what it means
> semantically; and why the proposed change is the best fix for the problem.
> 

I will surely add more explaination in v2.

> Also, why IS_ERR_OR_NULL()?
> 

I used IS_ERR_OR_NULL() to check if the 'hcon->amp_mgr' is a valid pointer or not, 
and unregister the 'hcon' and signal error, but will make changes in v2 with only
NULL check included, if you think it's incorrect to use IS_ERR check here along with
NULL.


Thanks,
Anmol Karn