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Melbin K Mathew c0e42fb0e0 vsock/virtio: cap TX credit to local buffer size 
[ Upstream commit 8ee784fdf0 ]

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: 06a8fc7836 ("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>
History 2026-01-30 10:28:43 +01:00
arch x86/kfence: avoid writing L1TF-vulnerable PTEs 2026-01-30 10:28:40 +01:00
block block: fix NULL pointer dereference in blk_zone_reset_all_bio_endio() 2026-01-08 10:15:06 +01:00
certs sign-file,extract-cert: use pkcs11 provider for OPENSSL MAJOR >= 3 2024-09-20 19:52:48 +03:00
crypto crypto: authencesn - reject too-short AAD (assoclen<8) to match ESP/ESN spec 2026-01-30 10:28:39 +01:00
Documentation fou: Don't allow 0 for FOU_ATTR_IPPROTO. 2026-01-30 10:28:39 +01:00
drivers octeontx2-af: Fix error handling 2026-01-30 10:28:43 +01:00
fs btrfs: fix missing fields in superblock backup with BLOCK_GROUP_TREE 2026-01-30 10:28:37 +01:00
include comedi: Fix getting range information for subdevices 16 to 255 2026-01-30 10:28:40 +01:00
init init: handle bootloader identifier in kernel parameters 2025-10-19 16:33:50 +02:00
io_uring io_uring/io-wq: check IO_WQ_BIT_EXIT inside work run loop 2026-01-30 10:28:41 +01:00
ipc ipc: fix to protect IPCS lookups using RCU 2025-06-27 11:11:22 +01:00
kernel sched/fair: Fix pelt clock sync when entering idle 2026-01-30 10:28:42 +01:00
lib lib/buildid: use __kernel_read() for sleepable context 2026-01-23 11:18:43 +01:00
LICENSES LICENSES: add 0BSD license text 2024-09-01 20:43:24 -07:00
mm mm/rmap: fix two comments related to huge_pmd_unshare() 2026-01-30 10:28:41 +01:00
net vsock/virtio: cap TX credit to local buffer size 2026-01-30 10:28:43 +01:00
rust rust: kbuild: workaround rustdoc doctests modifier bug 2025-11-24 10:36:07 +01:00
samples samples/ftrace: Adjust LoongArch register restore order in direct calls 2026-01-08 10:14:50 +01:00
scripts kconfig: fix static linking of nconf 2026-01-30 10:28:41 +01:00
security tpm2-sessions: Fix out of range indexing in name_size 2026-01-17 16:31:29 +01:00
sound ALSA: usb: Increase volume range that triggers a warning 2026-01-30 10:28:42 +01:00
tools vsock/test: fix seqpacket message bounds test 2026-01-30 10:28:43 +01:00
usr kbuild: uapi: Strip comments before size type check 2025-11-13 15:34:35 -05:00
virt KVM: Disallow toggling KVM_MEM_GUEST_MEMFD on an existing memslot 2026-01-08 10:14:21 +01:00
.clang-format clang-format: Update with v6.11-rc1's for_each macro list 2024-08-02 13:20:31 +02:00
.clippy.toml rust: give Clippy the minimum supported Rust version 2025-08-01 09:48:44 +01:00
.cocciconfig scripts: add Linux .cocciconfig for coccinelle 2016-07-22 12:13:39 +02:00
.editorconfig .editorconfig: remove trim_trailing_whitespace option 2024-06-13 16:47:52 +02:00
.get_maintainer.ignore Add Jeff Kirsher to .get_maintainer.ignore 2024-03-08 11:36:54 +00:00
.gitattributes .gitattributes: set diff driver for Rust source code files 2023-05-31 17:48:25 +02:00
.gitignore rust: introduce .clippy.toml 2025-03-13 13:01:42 +01:00
.mailmap mailmap: add entry for Thorsten Blum 2024-11-07 14:14:59 -08:00
.rustfmt.toml rust: add .rustfmt.toml 2022-09-28 09:02:20 +02:00
COPYING COPYING: state that all contributions really are covered by this file 2020-02-10 13:32:20 -08:00
CREDITS MAINTAINERS: Remove self from DSA entry 2024-11-03 12:52:38 -08:00
Kbuild Kbuild updates for v6.1 2022-10-10 12:00:45 -07:00
Kconfig kbuild: ensure full rebuild when the compiler is updated 2020-05-12 13:28:33 +09:00
MAINTAINERS staging: rtl8712: Remove driver using deprecated API wext 2025-12-07 06:25:02 +09:00
Makefile Linux 6.12.67 2026-01-23 11:18:52 +01:00
README README: Fix spelling 2024-03-18 03:36:32 -06:00

README 

Linux kernel
============

There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.

In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``.  The formatted documentation can also be read online at:

    https://www.kernel.org/doc/html/latest/

There are various text files in the Documentation/ subdirectory,
several of them using the reStructuredText markup notation.

Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.