Re: [PATCH] usb: gadget: f_fs: Fix use after free issue as part of queue failure

[Sriharsha Allenki <sallenki@codeaurora.org>]

Hi Greg,
On 3/26/2020 3:00 PM, Greg KH wrote:
> On Thu, Mar 26, 2020 at 02:14:23PM +0530, Sriharsha Allenki wrote:
>> Hi Greg,
>>
>> On 3/26/2020 1:46 PM, Greg KH wrote:
>>> On Thu, Mar 26, 2020 at 11:30:33AM +0530, Sriharsha Allenki wrote:
>>>> In AIO case, the request is freed up if ep_queue fails.
>>>> However, io_data->req still has the reference to this freed
>>>> request. In the case of this failure if there is aio_cancel
>>>> call on this io_data it will lead to an invalid dequeue
>>>> operation and a potential use after free issue.
>>>> Fix this by setting the io_data->req to NULL when the request
>>>> is freed as part of queue failure.
>>>>
>>>> Signed-off-by: Sriharsha Allenki <sallenki@codeaurora.org>
>>>> ---
>>>>  drivers/usb/gadget/function/f_fs.c | 1 +
>>>>  1 file changed, 1 insertion(+)
>>>>
>>>> diff --git a/drivers/usb/gadget/function/f_fs.c b/drivers/usb/gadget/function/f_fs.c
>>>> index 571917677d35..767f30b86645 100644
>>>> --- a/drivers/usb/gadget/function/f_fs.c
>>>> +++ b/drivers/usb/gadget/function/f_fs.c
>>>> @@ -1120,6 +1120,7 @@ static ssize_t ffs_epfile_io(struct file *file, struct ffs_io_data *io_data)
>>>>  
>>>>  		ret = usb_ep_queue(ep->ep, req, GFP_ATOMIC);
>>>>  		if (unlikely(ret)) {
>>>> +			io_data->req = NULL;
>>>>  			usb_ep_free_request(ep->ep, req);
>>>>  			goto error_lock;
>>>>  		}
>>>> -- 
>>>> The Qualcomm Innovation Center, Inc. is a member of the Code Aurora Forum, a Linux Foundation Collaborative Project
>>> What commit does this fix?  Should it go to stable kernels, and if so,
>>> how far back?
>> The commit 2e4c7553cd6f ("usb: gadget: f_fs: add aio support") introduced
>> the problem. It is good to have in stable kernels and it needs to go all
>> theway back to linux-3.15.y.
>>
>> Hope this information helps.
> Great, please resend this with the proper Fixes: and cc: stable... tag
> on it so that it gets picked up properly.
Thanks Greg for review. Sent out v2 patch with the updated tags.
> thanks,
>
> greg k-h
Regards,
Sriharsha