Re: [PATCH] net: bluetooth: Fix null pointer dereference in hci_event_packet()

[Eric Biggers]

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@xxxxxxxxxxxxxxxxxxxxxxxxx
> Link: https://syzkaller.appspot.com/bug?extid=0bef568258653cff272f
> Signed-off-by: Anmol Karn <anmol.karan123@xxxxxxxxx>
> ---
>  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;
> +	}
> +

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.

Also, why IS_ERR_OR_NULL()?

- Eric