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

Sriharsha Allenki
2020-03-26T08:44:43Z

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.
>
> thanks,
>
> greg k-h
Regards,
Sriharsha