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

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Date:   Sat, 12 Sep 2020 14:40:28 +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()

On Thu, Sep 10, 2020 at 01:49:18PM +0300, Dan Carpenter 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)) {
> 
> It can't be an error pointer.  Shouldn't we call hci_conn_del() on this
> path?  Try to find the Fixes tag to explain how this bug was introduced.
> 
> (Don't rush to send a v2.  The patch requires quite a bit more digging
> and detective work before it is ready).
> 
> > +		hci_dev_unlock(hdev);
> > +		return;
> > +	}
> > +
> >  	if (ev->status) {
> >  		hci_conn_del(hcon);
> >  		hci_dev_unlock(hdev);
> 
> regards,
> dan carpenter
> 

Sir,

I need little advice in continuing with this Patch,

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")


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);
+               return;
+       }
+
        if (ev->status) {
                hci_conn_del(hcon);
                hci_dev_unlock(hdev);


The value of 'hcon->amp_mgr' getting NULL due to hci_conn_hash_lookup_handle call
, and there is not any checks there for the members of hcon, which enables 
hci_phy_link_complete_evt() to dereference 'hcon->amp_mgr' as NULL.

please suggest improvements to this patch.

Regards,
Anmol