Subject: Re: [Linux-kernel-mentees] [PATCH] net: bluetooth: Fix null pointer deref in hci_phy_link_complete_evt

From: Anmol Karn <[email-masked]>
Date: Sun, 30 Aug 2020 17:56:23 +0530

On Sun, Aug 30, 2020 at 11:19:17AM +0200, Greg KH wrote:
> On Sat, Aug 29, 2020 at 10:27:12PM +0530, Anmol Karn wrote:
> > Fix null pointer deref in hci_phy_link_complete_evt, there was no 
> > checking there for the hcon->amp_mgr->l2cap_conn->hconn, and also 
> > in hci_cmd_work, for hdev->sent_cmd.
> > 
> > To fix this issue Add pointer checking in hci_cmd_work and
> > hci_phy_link_complete_evt.
> > [Linux-next-20200827]
> > 
> > This patch corrected some mistakes from previous patch.
> > 
> > Reported-by: [email-masked]
> > Link: https://syzkaller.appspot.com/bug?id=0d93140da5a82305a66a136af99b088b75177b99
> > Signed-off-by: Anmol Karn <[email-masked]>
> > ---
> >  net/bluetooth/hci_core.c  | 5 ++++-
> >  net/bluetooth/hci_event.c | 4 ++++
> >  2 files changed, 8 insertions(+), 1 deletion(-)
> > 
> > diff --git a/net/bluetooth/hci_core.c b/net/bluetooth/hci_core.c
> > index 68bfe57b6625..996efd654e7a 100644
> > --- a/net/bluetooth/hci_core.c
> > +++ b/net/bluetooth/hci_core.c
> > @@ -4922,7 +4922,10 @@ static void hci_cmd_work(struct work_struct *work)
> >  
> >  		kfree_skb(hdev->sent_cmd);
> >  
> > -		hdev->sent_cmd = skb_clone(skb, GFP_KERNEL);
> > +		if (hdev->sent_cmd) {
> > +			hdev->sent_cmd = skb_clone(skb, GFP_KERNEL);
> > +		}
> 
> How can sent_cmd be NULL here?  Are you sure something previous to this
> shouldn't be fixed instead?

Sir, sent_cmd was freed before this condition check, thats why i checked it,

i think i should check it before the free of hdev->sent_cmd like,

if (hdev->sent_cmd)
	kfree_skb(hdev->sent_cmd);

what's your opininon on this.

> 
> 
> > +
> >  		if (hdev->sent_cmd) {
> >  			if (hci_req_status_pend(hdev))
> >  				hci_dev_set_flag(hdev, HCI_CMD_PENDING);
> > diff --git a/net/bluetooth/hci_event.c b/net/bluetooth/hci_event.c
> > index 4b7fc430793c..1e7d9bee9111 100644
> > --- a/net/bluetooth/hci_event.c
> > +++ b/net/bluetooth/hci_event.c
> > @@ -4941,6 +4941,10 @@ static void hci_phy_link_complete_evt(struct hci_dev *hdev,
> >  		hci_dev_unlock(hdev);
> >  		return;
> >  	}
> > +	if (!(hcon->amp_mgr->l2cap_conn->hcon)) {
> > +		hci_dev_unlock(hdev);
> > +		return;
> > +	}
> 
> How can this be triggered?

syzbot showed that this line is accessed irrespective of the null value it contains, so  added a 
pointer check for that.

please give some opinions on this,

if (!bredr_hcon) {
	hci_dev_unlock(hdev);
        return;
}

Thanks,
Anmol Karn