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

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