CVE-2026-74310

Summary

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

vhost/net: complete zerocopy ubufs only once

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.

Affected Software

Weaknesses

References

• https://git.kernel.org/stable/c/ea71f873423fb73e66ad88936d6759ac0ad4aa53
• https://git.kernel.org/stable/c/6445b945024f4c7675ae5352b2d5885cb1deea71
• https://git.kernel.org/stable/c/a9f8a1d2e3ff511eafd4c5462481950c2f4d2b5d
• https://git.kernel.org/stable/c/321c73baf54d971ce3771fea275c98a247f7ee35
• https://git.kernel.org/stable/c/c069437924663539a93a1e5afe90838d9ccee284
• https://git.kernel.org/stable/c/8f6898fe80794f2d7c3d38c1158c806e4074a1c4

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