Re: [PATCH] media: videobuf2-core: copy vb planes unconditionally

[Tomasz Figa]

On Wed, Nov 6, 2024 at 9:18 PM Tudor Ambarus <tudor.ambarus@xxxxxxxxxx> wrote:
>
> Copy the relevant data from userspace to the vb->planes unconditionally
> as it's possible some of the fields may have changed after the buffer
> has been validated.
>
> Keep the dma_buf_put(planes[plane].dbuf) calls in the first
> `if (!reacquired)` case, in order to be close to the plane validation code
> where the buffers were got in the first place.
>
> Cc: stable@xxxxxxxxxxxxxxx
> Fixes: 95af7c00f35b ("media: videobuf2-core: release all planes first in __prepare_dmabuf()")
> Signed-off-by: Tudor Ambarus <tudor.ambarus@xxxxxxxxxx>
> ---
>  .../media/common/videobuf2/videobuf2-core.c   | 28 ++++++++++---------
>  1 file changed, 15 insertions(+), 13 deletions(-)
>

Thanks for the fix.

Acked-by: Tomasz Figa <tfiga@xxxxxxxxxxxx>

(We probably need some tests to verify this behavior... It seems like
the way v4l2-compliance is implemented [1] would only trigger the
!reacquired case on most drivers.)

[1] https://git.linuxtv.org/v4l-utils.git/tree/utils/v4l2-compliance/v4l2-test-buffers.cpp#n2071
(just queuing all imported buffers in order and re-queuing them
exactly as they are dequeued [2])
[2] https://git.linuxtv.org/v4l-utils.git/tree/utils/v4l2-compliance/v4l2-test-buffers.cpp#n1299

Best regards,
Tomasz

> diff --git a/drivers/media/common/videobuf2/videobuf2-core.c b/drivers/media/common/videobuf2/videobuf2-core.c
> index f07dc53a9d06..c0cc441b5164 100644
> --- a/drivers/media/common/videobuf2/videobuf2-core.c
> +++ b/drivers/media/common/videobuf2/videobuf2-core.c
> @@ -1482,18 +1482,23 @@ static int __prepare_dmabuf(struct vb2_buffer *vb)
>                         }
>                         vb->planes[plane].dbuf_mapped = 1;
>                 }
> +       } else {
> +               for (plane = 0; plane < vb->num_planes; ++plane)
> +                       dma_buf_put(planes[plane].dbuf);
> +       }
>
> -               /*
> -                * Now that everything is in order, copy relevant information
> -                * provided by userspace.
> -                */
> -               for (plane = 0; plane < vb->num_planes; ++plane) {
> -                       vb->planes[plane].bytesused = planes[plane].bytesused;
> -                       vb->planes[plane].length = planes[plane].length;
> -                       vb->planes[plane].m.fd = planes[plane].m.fd;
> -                       vb->planes[plane].data_offset = planes[plane].data_offset;
> -               }
> +       /*
> +        * Now that everything is in order, copy relevant information
> +        * provided by userspace.
> +        */
> +       for (plane = 0; plane < vb->num_planes; ++plane) {
> +               vb->planes[plane].bytesused = planes[plane].bytesused;
> +               vb->planes[plane].length = planes[plane].length;
> +               vb->planes[plane].m.fd = planes[plane].m.fd;
> +               vb->planes[plane].data_offset = planes[plane].data_offset;
> +       }
>
> +       if (reacquired) {
>                 /*
>                  * Call driver-specific initialization on the newly acquired buffer,
>                  * if provided.
> @@ -1503,9 +1508,6 @@ static int __prepare_dmabuf(struct vb2_buffer *vb)
>                         dprintk(q, 1, "buffer initialization failed\n");
>                         goto err_put_vb2_buf;
>                 }
> -       } else {
> -               for (plane = 0; plane < vb->num_planes; ++plane)
> -                       dma_buf_put(planes[plane].dbuf);
>         }
>
>         ret = call_vb_qop(vb, buf_prepare, vb);
> --
> 2.47.0.199.ga7371fff76-goog
>