From: Melbin K Mathew <mlbnkm1@gmail.com> stable inclusion from stable-v6.6.122 commit d9d5f222558b42f6277eafaaa6080966faf37676 category: feature bugzilla: https://atomgit.com/src-openeuler/kernel/issues/13619 CVE: CVE-2026-23086 Reference: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=... -------------------------------- [ Upstream commit 8ee784fdf006cbe8739cfa093f54d326cbf54037 ] The virtio transports derives its TX credit directly from peer_buf_alloc, which is set from the remote endpoint's SO_VM_SOCKETS_BUFFER_SIZE value. On the host side this means that the amount of data we are willing to queue for a connection is scaled by a guest-chosen buffer size, rather than the host's own vsock configuration. A malicious guest can advertise a large buffer and read slowly, causing the host to allocate a correspondingly large amount of sk_buff memory. The same thing would happen in the guest with a malicious host, since virtio transports share the same code base. Introduce a small helper, virtio_transport_tx_buf_size(), that returns min(peer_buf_alloc, buf_alloc), and use it wherever we consume peer_buf_alloc. This ensures the effective TX window is bounded by both the peer's advertised buffer and our own buf_alloc (already clamped to buffer_max_size via SO_VM_SOCKETS_BUFFER_MAX_SIZE), so a remote peer cannot force the other to queue more data than allowed by its own vsock settings. On an unpatched Ubuntu 22.04 host (~64 GiB RAM), running a PoC with 32 guest vsock connections advertising 2 GiB each and reading slowly drove Slab/SUnreclaim from ~0.5 GiB to ~57 GiB; the system only recovered after killing the QEMU process. That said, if QEMU memory is limited 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 MiB Only ~35 MiB increase in Slab/SUnreclaim, no host OOM, and the guest remains 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-V's 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 affects virtio-vsock, vhost-vsock, and loopback, bringing them in line with the "remote window intersected with local policy" behaviour that VMCI and Hyper-V already effectively have. Fixes: 06a8fc78367d ("VSOCK: Introduce virtio_vsock_common.ko") Suggested-by: Stefano Garzarella <sgarzare@redhat.com> Signed-off-by: Melbin K Mathew <mlbnkm1@gmail.com> [Stefano: small adjustments after changing the previous patch] [Stefano: tweak the commit message] Signed-off-by: Stefano Garzarella <sgarzare@redhat.com> Reviewed-by: Luigi Leonardi <leonardi@redhat.com> Link: https://patch.msgid.link/20260121093628.9941-4-sgarzare@redhat.com Acked-by: Michael S. Tsirkin <mst@redhat.com> Signed-off-by: Paolo Abeni <pabeni@redhat.com> Signed-off-by: Sasha Levin <sashal@kernel.org> Conflicts: net/vmw_vsock/virtio_transport_common.c [Conflicts due to context.] Signed-off-by: Ze Zuo <zuoze1@huawei.com> --- change since v1: -- fix patch merge conflict. --- net/vmw_vsock/virtio_transport_common.c | 14 ++++++++++++-- 1 file changed, 12 insertions(+), 2 deletions(-) diff --git a/net/vmw_vsock/virtio_transport_common.c b/net/vmw_vsock/virtio_transport_common.c index 1401177e2622..4c374c36c29d 100644 --- a/net/vmw_vsock/virtio_transport_common.c +++ b/net/vmw_vsock/virtio_transport_common.c @@ -628,6 +628,15 @@ virtio_transport_seqpacket_dequeue(struct vsock_sock *vsk, } EXPORT_SYMBOL_GPL(virtio_transport_seqpacket_dequeue); +static u32 virtio_transport_tx_buf_size(struct virtio_vsock_sock *vvs) +{ + /* The peer advertises its receive buffer via peer_buf_alloc, but we + * cap it to our local buf_alloc so a remote peer cannot force us to + * queue more data than our own buffer configuration allows. + */ + return min(vvs->peer_buf_alloc, vvs->buf_alloc); +} + int virtio_transport_seqpacket_enqueue(struct vsock_sock *vsk, struct msghdr *msg, @@ -637,7 +646,7 @@ virtio_transport_seqpacket_enqueue(struct vsock_sock *vsk, spin_lock_bh(&vvs->tx_lock); - if (len > vvs->peer_buf_alloc) { + if (len > virtio_transport_tx_buf_size(vvs)) { spin_unlock_bh(&vvs->tx_lock); return -EMSGSIZE; } @@ -691,7 +700,8 @@ static s64 virtio_transport_has_space(struct virtio_vsock_sock *vvs) * we have bytes in flight (tx_cnt - peer_fwd_cnt), the subtraction * does not underflow. */ - bytes = (s64)vvs->peer_buf_alloc - (vvs->tx_cnt - vvs->peer_fwd_cnt); + bytes = (s64)virtio_transport_tx_buf_size(vvs) - + (vvs->tx_cnt - vvs->peer_fwd_cnt); if (bytes < 0) bytes = 0; -- 2.25.1