On 6/1/26 12:43 PM, Qing Ming wrote:
> vhost-net initializes one ubuf_info per outstanding zerocopy TX
> descriptor and hands it to the backend socket. The networking stack may
> then clone a zerocopy skb before all skb references are released. For
> example, batman-adv fragmentation reaches skb_split(), which calls
> skb_zerocopy_clone() and increments the same ubuf_info refcount.
>
> vhost_zerocopy_complete() currently treats every ubuf callback as a
> completed vhost descriptor. It dereferences ubuf->ctx, writes the
> descriptor completion state, and drops the vhost_net_ubuf_ref even when
> the callback only releases a cloned skb reference. A backend reset can
> therefore wait for and free the vhost_net_ubuf_ref while another cloned
> skb still carries the same ubuf_info. A later completion then
> dereferences the freed ubufs pointer.
>
> KASAN reports the stale completion as:
>
> BUG: KASAN: slab-use-after-free in vhost_zerocopy_complete+0x1d7/0x1f0
> BUG: KASAN: slab-use-after-free in vhost_zerocopy_complete+0x101/0x1f0
> vhost_zerocopy_complete
> skb_copy_ubufs
> __dev_forward_skb2
> veth_xmit
>
> The freed object was allocated from vhost_net_ioctl() while setting the
> backend and freed through kfree_rcu()/kvfree_rcu_bulk after backend
> removal, while delayed skb completion still reached
> vhost_zerocopy_complete().
>
> Honor the generic ubuf_info refcount before touching vhost state, and run
> the vhost descriptor completion only for the final ubuf reference. This
> matches the msg_zerocopy_complete() ownership rule for cloned zerocopy
> skbs.
>
> Fixes: bab632d69ee4 ("vhost: vhost TX zero-copy support")
> Signed-off-by: Qing Ming <[email protected]>
The patch LGTM.
@Michael: to you want to take it via your tree?
/P
