Re: [PATCH v4 2/3] usb: gadget: uvc: Allocate uvc_requests one at a time

[Avichal Rakesh <arakesh@google.com>]

On 10/18/23 06:03, Michael Grzeschik wrote:
> A short second review.

Thank you for the review. Sent out a v5 with the comments 
addressed!

> 
> On Wed, Oct 11, 2023 at 05:24:50PM -0700, Avichal Rakesh wrote:
>> Currently, the uvc gadget driver allocates all uvc_requests as one array
>> and deallocates them all when the video stream stops. This includes
>> de-allocating all the usb_requests associated with those uvc_requests.
>> This can lead to use-after-free issues if any of those de-allocated
>> usb_requests were still owned by the usb controller.
>>
>> This patch is 1 of 2 patches addressing the use-after-free issue.
>> Instead of bulk allocating all uvc_requests as an array, this patch
>> allocates uvc_requests one at a time, which should allows for similar
>> granularity when deallocating the uvc_requests. This patch has no
>> functional changes other than allocating each uvc_request separately,
>> and similarly freeing each of them separately.
>>
>> Link: https://lore.kernel.org/7cd81649-2795-45b6-8c10-b7df1055020d@google.com
>> Suggested-by: Michael Grzeschik <m.grzeschik@pengutronix.de>
>> Reviewed-by: Michael Grzeschik <m.grzeschik@pengutronix.de>
>> Signed-off-by: Avichal Rakesh <arakesh@google.com>
>> ---
>> v1 -> v2: Rebased to ToT
>> v2 -> v3: Fix email threading goof-up
>> v3 -> v4: Address review comments & re-rebase to ToT
>>
>> drivers/usb/gadget/function/uvc.h       |  3 +-
>> drivers/usb/gadget/function/uvc_video.c | 87 ++++++++++++++-----------
>> 2 files changed, 50 insertions(+), 40 deletions(-)
>> -        if (video->ureq[i].req_buffer == NULL)
>> +        ureq->req_buffer = kmalloc(req_size, GFP_KERNEL);
>> +        if (ureq->req_buffer == NULL)
> You could also use if (!ureq->req_buffer)

Keeping this as is because I prefer `== NULL` check for readability.
Didn't find any specific rules in the kernel codestyle, so sticking
with the more readable option (in my opinion).

> 
>>             goto error;
>>
>> -        video->ureq[i].req = usb_ep_alloc_request(video->ep, GFP_KERNEL);
>> -        if (video->ureq[i].req == NULL)
>> +        ureq->req = usb_ep_alloc_request(video->ep, GFP_KERNEL);
>> +        if (ureq->req == NULL)
>>             goto error;
>>
>> -        video->ureq[i].req->buf = video->ureq[i].req_buffer;
>> -        video->ureq[i].req->length = 0;
>> -        video->ureq[i].req->complete = uvc_video_complete;
>> -        video->ureq[i].req->context = &video->ureq[i];
>> -        video->ureq[i].video = video;
>> -        video->ureq[i].last_buf = NULL;
>> +        ureq->req->buf = ureq->req_buffer;
>> +        ureq->req->length = 0;
>> +        ureq->req->complete = uvc_video_complete;
>> +        ureq->req->context = ureq;
>> +        ureq->video = video;
>> +        ureq->last_buf = NULL;
>>
>> -        list_add_tail(&video->ureq[i].req->list, &video->req_free);
>> +        list_add_tail(&ureq->req->list, &video->req_free);
>>         /* req_size/PAGE_SIZE + 1 for overruns and + 1 for header */
>> -        sg_alloc_table(&video->ureq[i].sgt,
>> +        sg_alloc_table(&ureq->sgt,
>>                    DIV_ROUND_UP(req_size - UVCG_REQUEST_HEADER_LEN,
>>                         PAGE_SIZE) + 2, GFP_KERNEL);
>>     }
>> @@ -489,8 +496,8 @@ static void uvcg_video_pump(struct work_struct *work)
>>  */
>> int uvcg_video_enable(struct uvc_video *video, int enable)
>> {
>> -    unsigned int i;
>>     int ret;
>> +    struct uvc_request *ureq;
>>
>>     if (video->ep == NULL) {
>>         uvcg_info(&video->uvc->func,
>> @@ -502,9 +509,10 @@ int uvcg_video_enable(struct uvc_video *video, int enable)
>>         cancel_work_sync(&video->pump);
>>         uvcg_queue_cancel(&video->queue, 0);
>>
>> -        for (i = 0; i < video->uvc_num_requests; ++i)
>> -            if (video->ureq && video->ureq[i].req)
>> -                usb_ep_dequeue(video->ep, video->ureq[i].req);
>> +        list_for_each_entry(ureq, &video->ureqs, list) {
>> +            if (ureq->req)
>> +                usb_ep_dequeue(video->ep, ureq->req);
>> +        }
>>
>>         uvc_video_free_requests(video);
>>         uvcg_queue_enable(&video->queue, 0);
>> @@ -536,6 +544,7 @@ int uvcg_video_enable(struct uvc_video *video, int enable)
>>  */
>> int uvcg_video_init(struct uvc_video *video, struct uvc_device *uvc)
>> {
>> +    INIT_LIST_HEAD(&video->ureqs);
>>     INIT_LIST_HEAD(&video->req_free);
>>     spin_lock_init(&video->req_lock);
>>     INIT_WORK(&video->pump, uvcg_video_pump);
>> -- 
>> 2.42.0.609.gbb76f46606-goog
>>
>>
>