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

[Greg KH <gregkh@linuxfoundation.org>]

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: syzbot+0bef568258653cff272f@syzkaller.appspotmail.com
> Link: https://syzkaller.appspot.com/bug?id=0d93140da5a82305a66a136af99b088b75177b99
> Signed-off-by: Anmol Karn <anmol.karan123@gmail.com>
> ---
>  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?


> +
>  		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?

thanks,

greg k-h
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