Merge branch 'vsock-virtio-fix-tx-credit-handling'

Stefano Garzarella says:

====================
vsock/virtio: fix TX credit handling

The original series was posted by Melbin K Mathew <mlbnkm1@gmail.com> till v4.
Since it's a real issue and the original author seems busy, I'm sending
the new version fixing my comments but keeping the authorship (and restoring
mine on patch 2 as reported on v4).

v5: https://lore.kernel.org/netdev/20260116201517.273302-1-sgarzare@redhat.com/
v4: https://lore.kernel.org/netdev/20251217181206.3681159-1-mlbnkm1@gmail.com/

From Melbin K Mathew <mlbnkm1@gmail.com>:

This series fixes TX credit handling in virtio-vsock:

Patch 1: Fix potential underflow in get_credit() using s64 arithmetic
Patch 2: Fix vsock_test seqpacket bounds test
Patch 3: Cap TX credit to local buffer size (security hardening)
Patch 4: Add stream TX credit bounds regression test

The core issue is that a malicious guest can advertise a huge buffer
size via SO_VM_SOCKETS_BUFFER_SIZE, causing the host to allocate
excessive sk_buff memory when sending data to that guest.

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.

With this series applied, the same PoC shows only ~35 MiB increase in
Slab/SUnreclaim, no host OOM, and the guest remains responsive.
====================

Link: https://patch.msgid.link/20260121093628.9941-1-sgarzare@redhat.com
Signed-off-by: Paolo Abeni <pabeni@redhat.com>