On Fri, Sep 06, 2019 at 02:06:59PM +0200, Matthias Lange wrote:
> The function virtqueue_add_split() DMA-maps the scatterlist buffers. In
> case a mapping error occurs the already mapped buffers must be unmapped.
> This happens by jumping to the 'unmap_release' label.
>
> In case of indirect descriptors the release is wrong and may leak kernel
> memory. Because the implementation assumes that the head descriptor is
> already mapped it starts iterating over the descriptor list starting
> from the head descriptor. However for indirect descriptors the head
> descriptor is never mapped in case of an error.
>
> The fix is to initialize the start index with zero in case of indirect
> descriptors and use the 'desc' pointer directly for iterating over the
> descriptor chain.
>
> This fix also changes the return code from EIO to ENOSPC in case of a
> mapping error. The reason is that drivers such as virtio_blk may retry
> their request and thus can recover from a mapping error.
>
> Signed-off-by: Matthias Lange <[email protected]>
Thanks for the patch!
However please, split this to 2 patches.
I think the 1st patch at least is a stable candidate.
About the return code part - could you please add a bit more explanation
in the commit log? E.g. document when does it trigger and what is the
effect of the fix. Thanks!
> ---
> drivers/virtio/virtio_ring.c | 10 +++++++---
> 1 file changed, 7 insertions(+), 3 deletions(-)
>
> diff --git a/drivers/virtio/virtio_ring.c b/drivers/virtio/virtio_ring.c
> index c8be1c4f5b55..d2e001f92e6e 100644
> --- a/drivers/virtio/virtio_ring.c
> +++ b/drivers/virtio/virtio_ring.c
> @@ -566,13 +566,17 @@ static inline int virtqueue_add_split(struct virtqueue
> *_vq,
>
> unmap_release:
> err_idx = i;
> - i = head;
> +
> + if (indirect)
> + i = 0;
> + else
> + i = head;
>
> for (n = 0; n < total_sg; n++) {
> if (i == err_idx)
> break;
> vring_unmap_one_split(vq, &desc[i]);
> - i = virtio16_to_cpu(_vq->vdev, vq->split.vring.desc[i].next);
> + i = virtio16_to_cpu(_vq->vdev, desc[i].next);
> }
>
> if (indirect)
> @@ -1081,7 +1085,7 @@ static int virtqueue_add_indirect_packed(struct
> vring_virtqueue *vq,
> kfree(desc);
>
> END_USE(vq);
> - return -EIO;
> + return -ENOSPC;
> }
>
> static inline int virtqueue_add_packed(struct virtqueue *_vq,
> --
> 2.17.1
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