Re: [PATCH v9 2/4] usb: gadget: uvc: Allocate uvc_requests one at a time

[Avichal Rakesh <arakesh@google.com>]

On 10/28/23 13:13, Dan Scally wrote:
> Hi Avichal
> 
> On 27/10/2023 21:19, 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: Daniel Scally <dan.scally@ideasonboard.com>
> 
> 
> Sorry - I was unclear in my response to the first patch on v8. I meant my R-b to apply to the first patch only rather than to all of them. For this one I understand now the use of the conditional in uvc_video_free_request(), so that point is fine. I agree with Greg that the BUG_ON() shouldn't stand though.

Ah, didn't realize BUG_ON is discouraged. Removed BUG_ON. 
It was supposed to be a defensive bit of code anyway, 
so removing the check entirely. If the state is 
inconsistent, we'd see other errors, so the BUG_ON 
wasn't providing value anyway.

Also removed your Reviewed-by, my apologies.

> 
>> Reviewed-by: Michael Grzeschik <m.grzeschik@pengutronix.de>
>> Tested-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
>> v4 -> v5: Address more review comments. Add Reviewed-by & Tested-by.
>> v5 -> v6: No change
>> v6 -> v7: No change
>> v7 -> v8: No change. Getting back in review queue
>> v8 -> v9: Address review comments.
>>
>>   drivers/usb/gadget/function/uvc.h       |  3 +-
>>   drivers/usb/gadget/function/uvc_video.c | 89 ++++++++++++++-----------
>>   2 files changed, 52 insertions(+), 40 deletions(-)
>>
>> diff --git a/drivers/usb/gadget/function/uvc.h b/drivers/usb/gadget/function/uvc.h
>> index 989bc6b4e93d..993694da0bbc 100644
>> --- a/drivers/usb/gadget/function/uvc.h
>> +++ b/drivers/usb/gadget/function/uvc.h
>> @@ -81,6 +81,7 @@ struct uvc_request {
>>       struct sg_table sgt;
>>       u8 header[UVCG_REQUEST_HEADER_LEN];
>>       struct uvc_buffer *last_buf;
>> +    struct list_head list;
>>   };
>>
>>   struct uvc_video {
>> @@ -102,7 +103,7 @@ struct uvc_video {
>>
>>       /* Requests */
>>       unsigned int req_size;
>> -    struct uvc_request *ureq;
>> +    struct list_head ureqs; /* all uvc_requests allocated by uvc_video */
>>       struct list_head req_free;
>>       spinlock_t req_lock;
>>
>> diff --git a/drivers/usb/gadget/function/uvc_video.c b/drivers/usb/gadget/function/uvc_video.c
>> index c334802ac0a4..f8f9209fee50 100644
>> --- a/drivers/usb/gadget/function/uvc_video.c
>> +++ b/drivers/usb/gadget/function/uvc_video.c
>> @@ -227,6 +227,24 @@ uvc_video_encode_isoc(struct usb_request *req, struct uvc_video *video,
>>    * Request handling
>>    */
>>
>> +static void
>> +uvc_video_free_request(struct uvc_request *ureq, struct usb_ep *ep)
>> +{
>> +    sg_free_table(&ureq->sgt);
>> +    if (ureq->req && ep) {
>> +        usb_ep_free_request(ep, ureq->req);
>> +        ureq->req = NULL;
>> +    }
>> +
>> +    kfree(ureq->req_buffer);
>> +    ureq->req_buffer = NULL;
>> +
>> +    if (!list_empty(&ureq->list))
>> +        list_del_init(&ureq->list);
>> +
>> +    kfree(ureq);
>> +}
>> +
>>   static int uvcg_video_ep_queue(struct uvc_video *video, struct usb_request *req)
>>   {
>>       int ret;
>> @@ -293,27 +311,12 @@ uvc_video_complete(struct usb_ep *ep, struct usb_request *req)
>>   static int
>>   uvc_video_free_requests(struct uvc_video *video)
>>   {
>> -    unsigned int i;
>> -
>> -    if (video->ureq) {
>> -        for (i = 0; i < video->uvc_num_requests; ++i) {
>> -            sg_free_table(&video->ureq[i].sgt);
>> +    struct uvc_request *ureq, *temp;
>>
>> -            if (video->ureq[i].req) {
>> -                usb_ep_free_request(video->ep, video->ureq[i].req);
>> -                video->ureq[i].req = NULL;
>> -            }
>> -
>> -            if (video->ureq[i].req_buffer) {
>> -                kfree(video->ureq[i].req_buffer);
>> -                video->ureq[i].req_buffer = NULL;
>> -            }
>> -        }
>> -
>> -        kfree(video->ureq);
>> -        video->ureq = NULL;
>> -    }
>> +    list_for_each_entry_safe(ureq, temp, &video->ureqs, list)
>> +        uvc_video_free_request(ureq, video->ep);
>>
>> +    INIT_LIST_HEAD(&video->ureqs);
>>       INIT_LIST_HEAD(&video->req_free);
>>       video->req_size = 0;
>>       return 0;
>> @@ -322,39 +325,45 @@ uvc_video_free_requests(struct uvc_video *video)
>>   static int
>>   uvc_video_alloc_requests(struct uvc_video *video)
>>   {
>> +    struct uvc_request *ureq;
>>       unsigned int req_size;
>>       unsigned int i;
>>       int ret = -ENOMEM;
>>
>>       BUG_ON(video->req_size);
>> +    BUG_ON(!list_empty(&video->ureqs));
>>
>>       req_size = video->ep->maxpacket
>>            * max_t(unsigned int, video->ep->maxburst, 1)
>>            * (video->ep->mult);
>>
>> -    video->ureq = kcalloc(video->uvc_num_requests, sizeof(struct uvc_request), GFP_KERNEL);
>> -    if (video->ureq == NULL)
>> -        return -ENOMEM;
>> +    for (i = 0; i < video->uvc_num_requests; i++) {
>> +        ureq = kzalloc(sizeof(struct uvc_request), GFP_KERNEL);
>> +        if (ureq == NULL)
>> +            goto error;
>> +
>> +        INIT_LIST_HEAD(&ureq->list);
>> +
>> +        list_add_tail(&ureq->list, &video->ureqs);
>>
>> -    for (i = 0; i < video->uvc_num_requests; ++i) {
>> -        video->ureq[i].req_buffer = kmalloc(req_size, GFP_KERNEL);
>> -        if (video->ureq[i].req_buffer == NULL)
>> +        ureq->req_buffer = kmalloc(req_size, GFP_KERNEL);
>> +        if (ureq->req_buffer == NULL)
>>               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 +498,8 @@ 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 +511,10 @@ 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 +546,7 @@ 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);
>> -- 
>> 2.42.0.820.g83a721a137-goog