From: Qing Ming <a0yami@mailbox.org> mainline inclusion from mainline-v7.2-rc1 commit 8f6898fe80794f2d7c3d38c1158c806e4074a1c4 category: bugfix bugzilla: https://atomgit.com/src-openeuler/kernel/issues/17657 CVE: CVE-2026-74310 Reference: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=... -------------------------------- 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 <a0yami@mailbox.org> Signed-off-by: Michael S. Tsirkin <mst@redhat.com> Message-ID: <20260601104300.197210-1-a0yami@mailbox.org> Conflicts: drivers/vhost/net.c [Fanhua Li: context conflict] Signed-off-by: Fanhua Li <lifanhua5@huawei.com> --- drivers/vhost/net.c | 12 +++++++++--- 1 file changed, 9 insertions(+), 3 deletions(-) diff --git a/drivers/vhost/net.c b/drivers/vhost/net.c index f5503306457f3..8539281fb1ef1 100644 --- a/drivers/vhost/net.c +++ b/drivers/vhost/net.c @@ -383,12 +383,18 @@ static void vhost_zerocopy_signal_used(struct vhost_net *net, static void vhost_zerocopy_callback(struct ubuf_info *ubuf, bool success) { - struct vhost_net_ubuf_ref *ubufs = ubuf->ctx; - struct vhost_virtqueue *vq = ubufs->vq; + struct vhost_net_ubuf_ref *ubufs; + struct vhost_virtqueue *vq; int cnt; - rcu_read_lock_bh(); + /* Only the final cloned skb reference completes the vhost descriptor. */ + if (!refcount_dec_and_test(&ubuf->refcnt)) + return; + + ubufs = ubuf->ctx; + vq = ubufs->vq; + rcu_read_lock_bh(); /* set len to mark this desc buffers done DMA */ vq->heads[ubuf->desc].len = success ? VHOST_DMA_DONE_LEN : VHOST_DMA_FAILED_LEN; -- 2.43.0