| lists.openwall.net | lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC | |
|
Open Source and information security mailing list archives
| ||
|
Message-ID: <ctubihgjn65za4hbmanhkzg7psr6kmj3jeqfj5sfxnnxjjvrsy@l6644u74vrn6>
Date: Thu, 11 Dec 2025 10:10:38 +0100
From: Stefano Garzarella <sgarzare@...hat.com>
To: Melbin K Mathew <mlbnkm1@...il.com>
Cc: stefanha@...hat.com, kvm@...r.kernel.org, netdev@...r.kernel.org,
virtualization@...ts.linux.dev, linux-kernel@...r.kernel.org, mst@...hat.com,
jasowang@...hat.com, xuanzhuo@...ux.alibaba.com, eperezma@...hat.com,
davem@...emloft.net, edumazet@...gle.com, kuba@...nel.org, pabeni@...hat.com,
horms@...nel.org
Subject: Re: [PATCH] vsock/virtio: cap TX credit to local buffer size
On Wed, Dec 10, 2025 at 04:00:19PM +0100, Melbin K Mathew wrote:
>The virtio vsock transport currently derives its TX credit directly
>from peer_buf_alloc, which is set from the remote endpoint's
>SO_VM_SOCKETS_BUFFER_SIZE value.
Why removing the target tree [net] from the tags?
Also this is a v2, so the tags should have been [PATCH net v2], please
check it in next versions, more info:
https://www.kernel.org/doc/html/latest/process/submitting-patches.html#subject-line
>
>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.
>
>Introduce a small helper, virtio_transport_peer_buf_alloc(), that
>returns min(peer_buf_alloc, buf_alloc), and use it wherever we consume
>peer_buf_alloc:
>
> - virtio_transport_get_credit()
> - virtio_transport_has_space()
> - virtio_transport_seqpacket_enqueue()
>
>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 guest
>cannot force the host to queue more data than allowed by the host's
>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 and the system only
>recovered after killing the QEMU process.
>
>With this patch applied, rerunning the same PoC yields:
>
> Before:
> MemFree: ~61.6 GiB
> MemAvailable: ~62.3 GiB
> Slab: ~142 MiB
> SUnreclaim: ~117 MiB
>
> After 32 high-credit connections:
> MemFree: ~61.5 GiB
> MemAvailable: ~62.3 GiB
> Slab: ~178 MiB
> SUnreclaim: ~152 MiB
>
>i.e. only ~35 MiB increase in Slab/SUnreclaim, no host OOM, and the
>guest remains responsive.
I think we should include here a summary of what you replied to Michael
about other transports.
I can't find your reply in the archive, but I mean the reply to
https://lore.kernel.org/netdev/20251210084318-mutt-send-email-mst@kernel.org/
>
>Fixes: 06a8fc78367d ("VSOCK: Introduce virtio_vsock_common.ko")
>Suggested-by: Stefano Garzarella <sgarzare@...hat.com>
>Signed-off-by: Melbin K Mathew <mlbnkm1@...il.com>
>---
> net/vmw_vsock/virtio_transport_common.c | 27 ++++++++++++++++++++++---
> 1 file changed, 24 insertions(+), 3 deletions(-)
>
>diff --git a/net/vmw_vsock/virtio_transport_common.c b/net/vmw_vsock/virtio_transport_common.c
>index dcc8a1d58..02eeb96dd 100644
>--- a/net/vmw_vsock/virtio_transport_common.c
>+++ b/net/vmw_vsock/virtio_transport_common.c
>@@ -491,6 +491,25 @@ void virtio_transport_consume_skb_sent(struct sk_buff *skb, bool consume)
> }
> EXPORT_SYMBOL_GPL(virtio_transport_consume_skb_sent);
>
>+/*
>+ * Return the effective peer buffer size for TX credit computation.
nit: block comment in this file doesn't leave empty line, so I'd follow
it:
@@ -491,8 +491,7 @@ void virtio_transport_consume_skb_sent(struct sk_buff *skb, bool consume)
}
EXPORT_SYMBOL_GPL(virtio_transport_consume_skb_sent);
-/*
- * Return the effective peer buffer size for TX credit computation.
+/* Return the effective peer buffer size for TX credit computation.
*
* The peer advertises its receive buffer via peer_buf_alloc, but we
* cap that to our local buf_alloc (derived from
>+ *
>+ * The peer advertises its receive buffer via peer_buf_alloc, but we
>+ * cap that to our local buf_alloc (derived from
>+ * SO_VM_SOCKETS_BUFFER_SIZE and already clamped to buffer_max_size)
>+ * so that a remote endpoint cannot force us to queue more data than
>+ * our own configuration allows.
>+ */
>+static u32 virtio_transport_tx_buf_alloc(struct virtio_vsock_sock *vvs)
>+{
>+ u32 peer = vvs->peer_buf_alloc;
>+ u32 local = vvs->buf_alloc;
>+
>+ if (peer > local)
>+ return local;
>+ return peer;
>+}
>+
I think here Michael was suggesting this:
@@ -502,12 +502,7 @@ EXPORT_SYMBOL_GPL(virtio_transport_consume_skb_sent);
*/
static u32 virtio_transport_tx_buf_alloc(struct virtio_vsock_sock *vvs)
{
- u32 peer = vvs->peer_buf_alloc;
- u32 local = vvs->buf_alloc;
-
- if (peer > local)
- return local;
- return peer;
+ return min(vvs->peer_buf_alloc, vvs->buf_alloc);
}
> u32 virtio_transport_get_credit(struct virtio_vsock_sock *vvs, u32 credit)
> {
> u32 ret;
>@@ -499,7 +518,8 @@ u32 virtio_transport_get_credit(struct virtio_vsock_sock *vvs, u32 credit)
> return 0;
>
> spin_lock_bh(&vvs->tx_lock);
>- ret = vvs->peer_buf_alloc - (vvs->tx_cnt - vvs->peer_fwd_cnt);
>+ ret = virtio_transport_tx_buf_alloc(vvs) -
>+ (vvs->tx_cnt - vvs->peer_fwd_cnt);
> if (ret > credit)
> ret = credit;
> vvs->tx_cnt += ret;
>@@ -831,7 +851,7 @@ 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_alloc(vvs)) {
> spin_unlock_bh(&vvs->tx_lock);
> return -EMSGSIZE;
> }
>@@ -882,7 +902,8 @@ static s64 virtio_transport_has_space(struct vsock_sock *vsk)
> struct virtio_vsock_sock *vvs = vsk->trans;
> s64 bytes;
>
>- bytes = (s64)vvs->peer_buf_alloc - (vvs->tx_cnt - vvs->peer_fwd_cnt);
>+ bytes = (s64)virtio_transport_tx_buf_alloc(vvs) -
>+ (vvs->tx_cnt - vvs->peer_fwd_cnt);
nit: please align this:
@@ -903,7 +898,7 @@ static s64 virtio_transport_has_space(struct vsock_sock *vsk)
s64 bytes;
bytes = (s64)virtio_transport_tx_buf_alloc(vvs) -
- (vvs->tx_cnt - vvs->peer_fwd_cnt);
+ (vvs->tx_cnt - vvs->peer_fwd_cnt);
if (bytes < 0)
bytes = 0;
Just minor things, but the patch LGTM, thanks!
Stefano
> if (bytes < 0)
> bytes = 0;
>
>--
>2.34.1
>
Powered by blists - more mailing lists