On Fri, Jun 10, 2022 at 06:33:14PM +0800, huangjie.albert wrote:
> ksoftirqd may consume the packet and it will call:
> virtnet_poll
> -->virtnet_receive
> -->virtqueue_get_buf_ctx
> -->virtqueue_get_buf_ctx_packed
> and in virtqueue_get_buf_ctx_packed:
>
> vq->last_used_idx += vq->packed.desc_state[id].num;
> if (unlikely(vq->last_used_idx >= vq->packed.vring.num)) {
> vq->last_used_idx -= vq->packed.vring.num;
> vq->packed.used_wrap_counter ^= 1;
> }
>
> if at the same time, there comes a vring interrupt，in vring_interrupt:
> we will call:
> vring_interrupt
> -->more_used
> -->more_used_packed
> -->is_used_desc_packed
> in is_used_desc_packed, the last_used_idx maybe >= vq->packed.vring.num.
> so this could case a memory out of bounds bug.
>
> this patch is to fix this.
>
> Signed-off-by: huangjie.albert <huangjie.albert@xxxxxxxxxxxxx>
This pattern was always iffy, but I don't think the patch
improves the situation much. last_used_idx and vq->packed.used_wrap_counter
can still get out of sync.
Maybe refactor code to keep everything in vq->last_used_idx?
Jason what is your take?
> ---
> drivers/virtio/virtio_ring.c | 3 +++
> 1 file changed, 3 insertions(+)
>
> diff --git a/drivers/virtio/virtio_ring.c b/drivers/virtio/virtio_ring.c
> index 13a7348cedff..d2abbb3a8187 100644
> --- a/drivers/virtio/virtio_ring.c
> +++ b/drivers/virtio/virtio_ring.c
> @@ -1397,6 +1397,9 @@ static inline bool is_used_desc_packed(const struct vring_virtqueue *vq,
> bool avail, used;
> u16 flags;
>
> + if (idx >= vq->packed.vring.num)
> + return false;
> +
> flags = le16_to_cpu(vq->packed.vring.desc[idx].flags);
> avail = !!(flags & (1 << VRING_PACKED_DESC_F_AVAIL));
> used = !!(flags & (1 << VRING_PACKED_DESC_F_USED));
> --
> 2.27.0
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