Re: [PATCH] nfc: virtual_ncidev: Add variable to check if ndev is running

Krzysztof Kozlowski
2023-11-20T09:06:19Z

On 20/11/2023 05:47, Bongsu Jeon wrote:
>
> On 20/11/2023 01:47, Nguyen Dinh Phi wrote:
>
>> syzbot reported an memory leak that happens when an skb is add to
>> send_buff after virtual nci closed.
>> This patch adds a variable to track if the ndev is running before
>> handling new skb in send function.
>>
>> Reported-by: syzbot+6eb09d75211863f15e3e@syzkaller.appspotmail.com
>> Closes: https://lore.kernel.org/lkml/00000000000075472b06007df4fb@google.com
>> Signed-off-by: Nguyen Dinh Phi <phind.uet@gmail.com>
>> ---
>> drivers/nfc/virtual_ncidev.c | 9 +++++++--
>> 1 file changed, 7 insertions(+), 2 deletions(-)
>>
>> diff --git a/drivers/nfc/virtual_ncidev.c b/drivers/nfc/virtual_ncidev.c
>> index b027be0b0b6f..ac8226db54e2 100644
>> --- a/drivers/nfc/virtual_ncidev.c
>> +++ b/drivers/nfc/virtual_ncidev.c
>> @@ -20,26 +20,31 @@
>> NFC_PROTO_ISO14443_MASK | \
>> NFC_PROTO_ISO14443_B_MASK | \
>> NFC_PROTO_ISO15693_MASK)
>> +#define NCIDEV_RUNNING 0
> This define isn't used.
>
>>
>> struct virtual_nci_dev {
>> struct nci_dev *ndev;
>> struct mutex mtx;
>> struct sk_buff *send_buff;
>> struct wait_queue_head wq;
>> + bool running;
>> };
>>
>> static int virtual_nci_open(struct nci_dev *ndev)
>> {
>> + struct virtual_nci_dev *vdev = nci_get_drvdata(ndev);
>> +
>> + vdev->running = true;
>> return 0;
>> }
>>
>> static int virtual_nci_close(struct nci_dev *ndev)
>> {
>> struct virtual_nci_dev *vdev = nci_get_drvdata(ndev);
>> -
>> mutex_lock(&vdev->mtx);
>> kfree_skb(vdev->send_buff);
>> vdev->send_buff = NULL;
>> + vdev->running = false;
>> mutex_unlock(&vdev->mtx);
>>
>> return 0;
>> @@ -50,7 +55,7 @@ static int virtual_nci_send(struct nci_dev *ndev, struct sk_buff *skb)
>> struct virtual_nci_dev *vdev = nci_get_drvdata(ndev);
>>
>> mutex_lock(&vdev->mtx);
>> - if (vdev->send_buff) {
>> + if (vdev->send_buff || !vdev->running) {
>
> Dear Krzysztof,
>
> I agree this defensive code.
> But i think NFC submodule has to avoid this situation.(calling send function of closed nci_dev)
> Could you check this?

This code looks not effective. At this point vdev->send_buff is always
false, so the additional check would not bring any value.

I don't see this fixing anything. Syzbot also does not seem to agree.

Nguyen, please test your patches against syzbot *before* sending them.
If you claim this fixes the report, please provide me the link to syzbot
test results confirming it is fixed.

I looked at syzbot dashboard and do not see this issue fixed with this
patch.

Best regards,
Krzysztof