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

Nguyen Dinh Phi
2023-11-20T10:39:55Z

On 20/11/23 5:06 pm, Krzysztof Kozlowski wrote:
> 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
>

Hi Krzysztof,

I've submitted it to syzbot, it is the test request that created at
[2023/11/20 09:39] in dashboard link
https://syzkaller.appspot.com/bug?extid=6eb09d75211863f15e3e

Best regards,
Phi