CVE-2026-74310

In the Linux kernel, the following vulnerability has been resolved:

vhost/net: complete zerocopy ubufs only once

vhost-net initializes one ubufinfo 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 skbsplit(), which calls skbzerocopyclone() and increments the same ubuf_info refcount.

vhostzerocopycomplete() currently treats every ubuf callback as a completed vhost descriptor. It dereferences ubuf->ctx, writes the descriptor completion state, and drops the vhostnetubufref even when the callback only releases a cloned skb reference. A backend reset can therefore wait for and free the vhostnetubufref 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 vhostzerocopycomplete+0x1d7/0x1f0 BUG: KASAN: slab-use-after-free in vhostzerocopycomplete+0x101/0x1f0 vhostzerocopycomplete skbcopyubufs _devforwardskb2 vethxmit

The freed object was allocated from vhostnetioctl() while setting the backend and freed through kfreercu()/kvfreercubulk after backend removal, while delayed skb completion still reached vhostzerocopy_complete().

Honor the generic ubufinfo refcount before touching vhost state, and run the vhost descriptor completion only for the final ubuf reference. This matches the msgzerocopy_complete() ownership rule for cloned zerocopy skbs.