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

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Date:   Tue, 15 Sep 2020 00:07:34 +0530
From:   Anmol Karn <anmol.karan123@...il.com>
To:     Dan Carpenter <dan.carpenter@...cle.com>
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: [Linux-kernel-mentees] [PATCH] net: bluetooth: Fix null pointer
 dereference in hci_event_packet()

Hello Sir,
 
> > I have looked into the Bisected logs and the problem occurs from this commit:
> > 
> > 941992d29447 ("ethernet: amd: use IS_ENABLED() instead of checking for built-in or module")
> > 
> 
> That's just the patch which made the code testable by syzbot.  It didn't
> introduce the bug.
> 
> > 
> > Here is a diff of patch which i modified from last patch,
> > 
> > diff --git a/net/bluetooth/hci_event.c b/net/bluetooth/hci_event.c
> > index 4b7fc430793c..6ce435064e0b 100644
> > --- a/net/bluetooth/hci_event.c
> > +++ b/net/bluetooth/hci_event.c
> > @@ -4936,6 +4936,12 @@ static void hci_phy_link_complete_evt(struct hci_dev *hdev,
> >                 return;
> >         }
> > 
> > +       if (!hcon->amp_mgr) {
> > +               hci_conn_del(hcon);
> > +               hci_dev_unlock(hdev);
> 
> I have no idea if calling hci_conn_del() is really the correct, thing.
> I don't know the code at all.  Anyway, do some research and figure out
> for sure what the correct thing is.

I have created my patch on the basis of the already applied conditions handling
in this function, i.e whenever NULL dereference occurs, connection cleanup is 
required hence, hci_conn_del() is used here. Will see if anything else could be
done.

> 
> Also look for similar bugs in other places where hcon->amp_mgr is
> dereferenced.  For example, amp_read_loc_assoc_final_data() seems to
> have a similar bug.
> 

Sure sir will look into it.

> regards,
> dan carpenter
> 

Thanks,
Anmol