CVE-2026-23086

Description

In the Linux kernel, the following vulnerability has been resolved:vsock/virtio: cap TX credit to local buffer sizeThe virtio transports derives its TX credit directly from peer_buf_alloc,which is set from the remote endpoints SO_VM_SOCKETS_BUFFER_SIZE value.On the host side this means that the amount of data we are willing toqueue for a connection is scaled by a guest-chosen buffer size, ratherthan the hosts own vsock configuration. A malicious guest can advertisea large buffer and read slowly, causing the host to allocate acorrespondingly large amount of sk_buff memory.The same thing would happen in the guest with a malicious host, sincevirtio transports share the same code base.Introduce a small helper, virtio_transport_tx_buf_size(), thatreturns min(peer_buf_alloc, buf_alloc), and use it wherever we consumepeer_buf_alloc.This ensures the effective TX window is bounded by both the peersadvertised buffer and our own buf_alloc (already clamped tobuffer_max_size via SO_VM_SOCKETS_BUFFER_MAX_SIZE), so a remote peercannot force the other to queue more data than allowed by its ownvsock settings.On an unpatched Ubuntu 22.04 host (~64 GiB RAM), running a PoC with32 guest vsock connections advertising 2 GiB each and reading slowlydrove Slab/SUnreclaim from ~0.5 GiB to ~57 GiB; the system onlyrecovered after killing the QEMU process. That said, if QEMU memory islimited with cgroups, the maximum memory used will be limited.With this patch applied: Before: MemFree: ~61.6 GiB Slab: ~142 MiB SUnreclaim: ~117 MiB After 32 high-credit connections: MemFree: ~61.5 GiB Slab: ~178 MiB SUnreclaim: ~152 MiBOnly ~35 MiB increase in Slab/SUnreclaim, no host OOM, and the guestremains responsive.Compatibility with non-virtio transports: - VMCI uses the AF_VSOCK buffer knobs to size its queue pairs per socket based on the local vsk->buffer_* values; the remote side cannot enlarge those queues beyond what the local endpoint configured. - Hyper-Vs vsock transport uses fixed-size VMBus ring buffers and an MTU bound; there is no peer-controlled credit field comparable to peer_buf_alloc, and the remote endpoint cannot drive in-flight kernel memory above those ring sizes. - The loopback path reuses virtio_transport_common.c, so it naturally follows the same semantics as the virtio transport.This change is limited to virtio_transport_common.c and thus affectsvirtio-vsock, vhost-vsock, and loopback, bringing them in line with theremote window intersected with local policy behaviour that VMCI andHyper-V already effectively have.[Stefano: small adjustments after changing the previous patch][Stefano: tweak the commit message]

Risk Information

Associated Vulnerability

Patch Details

References

https://nvd.nist.gov/vuln/detail/CVE-2023-1234
https://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2023-1234