[PATCH net] vsock/virtio: fix potential unbounded skb queue

[PATCH net] vsock/virtio: fix potential unbounded skb queue

[Eric Dumazet]

virtio_transport_inc_rx_pkt() checks vvs->rx_bytes + len > vvs->buf_alloc.

virtio_transport_recv_enqueue() skips coalescing for packets
with VIRTIO_VSOCK_SEQ_EOM.

If fed with packets with len == 0 and VIRTIO_VSOCK_SEQ_EOM,
a very large number of packets can be queued
because vvs->rx_bytes stays at 0.

Fix this by estimating the skb metadata size:

	(Number of skbs in the queue) * SKB_TRUESIZE(0)

Fixes: 077706165717 ("virtio/vsock: don't use skbuff state to account credit")
Signed-off-by: Eric Dumazet <edumazet@google.com>
Cc: Arseniy Krasnov <AVKrasnov@sberdevices.ru>
Cc: Stefan Hajnoczi <stefanha@redhat.com>
Cc: Stefano Garzarella <sgarzare@redhat.com>
Cc: "Michael S. Tsirkin" <mst@redhat.com>
Cc: Jason Wang <jasowang@redhat.com>
Cc: Xuan Zhuo <xuanzhuo@linux.alibaba.com>
Cc: "Eugenio Pérez" <eperezma@redhat.com>
Cc: kvm@vger.kernel.org
Cc: virtualization@lists.linux.dev
---
 net/vmw_vsock/virtio_transport_common.c | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/net/vmw_vsock/virtio_transport_common.c b/net/vmw_vsock/virtio_transport_common.c
index 416d533f493d7b07e9c77c43f741d28cfcd0953e..9b8014516f4fb1130ae184635fbba4dfee58bd64 100644
--- a/net/vmw_vsock/virtio_transport_common.c
+++ b/net/vmw_vsock/virtio_transport_common.c
@@ -447,7 +447,9 @@ static int virtio_transport_send_pkt_info(struct vsock_sock *vsk,
 static bool virtio_transport_inc_rx_pkt(struct virtio_vsock_sock *vvs,
 					u32 len)
 {
-	if (vvs->buf_used + len > vvs->buf_alloc)
+	u64 skb_overhead = (skb_queue_len(&vvs->rx_queue) + 1) * SKB_TRUESIZE(0);
+
+	if (skb_overhead + vvs->buf_used + len > vvs->buf_alloc)
 		return false;
 
 	vvs->rx_bytes += len;
-- 
2.54.0.545.g6539524ca2-goog

Re: [PATCH net] vsock/virtio: fix potential unbounded skb queue

[patchwork-bot+netdevbpf]

Hello:

This patch was applied to netdev/net.git (main)
by Jakub Kicinski <kuba@kernel.org>:

On Thu, 30 Apr 2026 12:26:52 +0000 you wrote:
> virtio_transport_inc_rx_pkt() checks vvs->rx_bytes + len > vvs->buf_alloc.
> 
> virtio_transport_recv_enqueue() skips coalescing for packets
> with VIRTIO_VSOCK_SEQ_EOM.
> 
> If fed with packets with len == 0 and VIRTIO_VSOCK_SEQ_EOM,
> a very large number of packets can be queued
> because vvs->rx_bytes stays at 0.
> 
> [...]

Here is the summary with links:
  - [net] vsock/virtio: fix potential unbounded skb queue
    https://git.kernel.org/netdev/net/c/059b7dbd20a6

You are awesome, thank you!
-- 
Deet-doot-dot, I am a bot.
https://korg.docs.kernel.org/patchwork/pwbot.html

Re: [PATCH net] vsock/virtio: fix potential unbounded skb queue

[Stefano Garzarella]

On Thu, Apr 30, 2026 at 12:26:52PM +0000, Eric Dumazet wrote:
>virtio_transport_inc_rx_pkt() checks vvs->rx_bytes + len > vvs->buf_alloc.
>
>virtio_transport_recv_enqueue() skips coalescing for packets
>with VIRTIO_VSOCK_SEQ_EOM.
>
>If fed with packets with len == 0 and VIRTIO_VSOCK_SEQ_EOM,
>a very large number of packets can be queued
>because vvs->rx_bytes stays at 0.
>
>Fix this by estimating the skb metadata size:
>
>	(Number of skbs in the queue) * SKB_TRUESIZE(0)
>
>Fixes: 077706165717 ("virtio/vsock: don't use skbuff state to account credit")
>Signed-off-by: Eric Dumazet <edumazet@google.com>
>Cc: Arseniy Krasnov <AVKrasnov@sberdevices.ru>
>Cc: Stefan Hajnoczi <stefanha@redhat.com>
>Cc: Stefano Garzarella <sgarzare@redhat.com>
>Cc: "Michael S. Tsirkin" <mst@redhat.com>
>Cc: Jason Wang <jasowang@redhat.com>
>Cc: Xuan Zhuo <xuanzhuo@linux.alibaba.com>
>Cc: "Eugenio Pérez" <eperezma@redhat.com>
>Cc: kvm@vger.kernel.org
>Cc: virtualization@lists.linux.dev
>---
> net/vmw_vsock/virtio_transport_common.c | 4 +++-
> 1 file changed, 3 insertions(+), 1 deletion(-)
>
>diff --git a/net/vmw_vsock/virtio_transport_common.c b/net/vmw_vsock/virtio_transport_common.c
>index 416d533f493d7b07e9c77c43f741d28cfcd0953e..9b8014516f4fb1130ae184635fbba4dfee58bd64 100644
>--- a/net/vmw_vsock/virtio_transport_common.c
>+++ b/net/vmw_vsock/virtio_transport_common.c
>@@ -447,7 +447,9 @@ static int virtio_transport_send_pkt_info(struct vsock_sock *vsk,
> static bool virtio_transport_inc_rx_pkt(struct virtio_vsock_sock *vvs,
> 					u32 len)
> {
>-	if (vvs->buf_used + len > vvs->buf_alloc)
>+	u64 skb_overhead = (skb_queue_len(&vvs->rx_queue) + 1) * SKB_TRUESIZE(0);
>+
>+	if (skb_overhead + vvs->buf_used + len > vvs->buf_alloc)
> 		return false;

I'm not sure about this fix, I mean that maybe this is incomplete.
In virtio-vsock, there is a credit mechanism between the two peers:
https://docs.oasis-open.org/virtio/virtio/v1.3/csd01/virtio-v1.3-csd01.html#x1-4850003

This takes only the payload into account, so it’s true that this problem 
exists; however, perhaps we should also inform the other peer of a lower 
credit balance, otherwise the other peer will believe it has much more 
credit than it actually does, send a large payload, and then the packet 
will be discarded and the data lost (there are no retransmissions, 
etc.).

Thanks,
Stefano

Re: [PATCH net] vsock/virtio: fix potential unbounded skb queue

[Eric Dumazet]

On Tue, May 5, 2026 at 6:52 AM Stefano Garzarella <sgarzare@redhat.com> wrote:
>
> On Thu, Apr 30, 2026 at 12:26:52PM +0000, Eric Dumazet wrote:
> >virtio_transport_inc_rx_pkt() checks vvs->rx_bytes + len > vvs->buf_alloc.
> >
> >virtio_transport_recv_enqueue() skips coalescing for packets
> >with VIRTIO_VSOCK_SEQ_EOM.
> >
> >If fed with packets with len == 0 and VIRTIO_VSOCK_SEQ_EOM,
> >a very large number of packets can be queued
> >because vvs->rx_bytes stays at 0.
> >
> >Fix this by estimating the skb metadata size:
> >
> >       (Number of skbs in the queue) * SKB_TRUESIZE(0)
> >
> >Fixes: 077706165717 ("virtio/vsock: don't use skbuff state to account credit")
> >Signed-off-by: Eric Dumazet <edumazet@google.com>
> >Cc: Arseniy Krasnov <AVKrasnov@sberdevices.ru>
> >Cc: Stefan Hajnoczi <stefanha@redhat.com>
> >Cc: Stefano Garzarella <sgarzare@redhat.com>
> >Cc: "Michael S. Tsirkin" <mst@redhat.com>
> >Cc: Jason Wang <jasowang@redhat.com>
> >Cc: Xuan Zhuo <xuanzhuo@linux.alibaba.com>
> >Cc: "Eugenio Pérez" <eperezma@redhat.com>
> >Cc: kvm@vger.kernel.org
> >Cc: virtualization@lists.linux.dev
> >---
> > net/vmw_vsock/virtio_transport_common.c | 4 +++-
> > 1 file changed, 3 insertions(+), 1 deletion(-)
> >
> >diff --git a/net/vmw_vsock/virtio_transport_common.c b/net/vmw_vsock/virtio_transport_common.c
> >index 416d533f493d7b07e9c77c43f741d28cfcd0953e..9b8014516f4fb1130ae184635fbba4dfee58bd64 100644
> >--- a/net/vmw_vsock/virtio_transport_common.c
> >+++ b/net/vmw_vsock/virtio_transport_common.c
> >@@ -447,7 +447,9 @@ static int virtio_transport_send_pkt_info(struct vsock_sock *vsk,
> > static bool virtio_transport_inc_rx_pkt(struct virtio_vsock_sock *vvs,
> >                                       u32 len)
> > {
> >-      if (vvs->buf_used + len > vvs->buf_alloc)
> >+      u64 skb_overhead = (skb_queue_len(&vvs->rx_queue) + 1) * SKB_TRUESIZE(0);
> >+
> >+      if (skb_overhead + vvs->buf_used + len > vvs->buf_alloc)
> >               return false;
>
> I'm not sure about this fix, I mean that maybe this is incomplete.
> In virtio-vsock, there is a credit mechanism between the two peers:
> https://docs.oasis-open.org/virtio/virtio/v1.3/csd01/virtio-v1.3-csd01.html#x1-4850003
>
> This takes only the payload into account, so it’s true that this problem
> exists; however, perhaps we should also inform the other peer of a lower
> credit balance, otherwise the other peer will believe it has much more
> credit than it actually does, send a large payload, and then the packet
> will be discarded and the data lost (there are no retransmissions,
> etc.).

I dunno, perhaps revert 077706165717 ("virtio/vsock: don't use skbuff
state to account credit")
and find a better fix then?

There is always a discrepancy between skb->len and skb->truesize.
You will not be able to announce a 1MB window, and accept one milliion
skb of 1-byte each.

This kind of contract is broken.

Re: [PATCH net] vsock/virtio: fix potential unbounded skb queue

[Stefano Garzarella]

On Tue, May 05, 2026 at 07:14:36AM -0700, Eric Dumazet wrote:
>On Tue, May 5, 2026 at 6:52 AM Stefano Garzarella <sgarzare@redhat.com> wrote:
>>
>> On Thu, Apr 30, 2026 at 12:26:52PM +0000, Eric Dumazet wrote:
>> >virtio_transport_inc_rx_pkt() checks vvs->rx_bytes + len > vvs->buf_alloc.
>> >
>> >virtio_transport_recv_enqueue() skips coalescing for packets
>> >with VIRTIO_VSOCK_SEQ_EOM.
>> >
>> >If fed with packets with len == 0 and VIRTIO_VSOCK_SEQ_EOM,
>> >a very large number of packets can be queued
>> >because vvs->rx_bytes stays at 0.
>> >
>> >Fix this by estimating the skb metadata size:
>> >
>> >       (Number of skbs in the queue) * SKB_TRUESIZE(0)
>> >
>> >Fixes: 077706165717 ("virtio/vsock: don't use skbuff state to account credit")
>> >Signed-off-by: Eric Dumazet <edumazet@google.com>
>> >Cc: Arseniy Krasnov <AVKrasnov@sberdevices.ru>
>> >Cc: Stefan Hajnoczi <stefanha@redhat.com>
>> >Cc: Stefano Garzarella <sgarzare@redhat.com>
>> >Cc: "Michael S. Tsirkin" <mst@redhat.com>
>> >Cc: Jason Wang <jasowang@redhat.com>
>> >Cc: Xuan Zhuo <xuanzhuo@linux.alibaba.com>
>> >Cc: "Eugenio Pérez" <eperezma@redhat.com>
>> >Cc: kvm@vger.kernel.org
>> >Cc: virtualization@lists.linux.dev
>> >---
>> > net/vmw_vsock/virtio_transport_common.c | 4 +++-
>> > 1 file changed, 3 insertions(+), 1 deletion(-)
>> >
>> >diff --git a/net/vmw_vsock/virtio_transport_common.c b/net/vmw_vsock/virtio_transport_common.c
>> >index 416d533f493d7b07e9c77c43f741d28cfcd0953e..9b8014516f4fb1130ae184635fbba4dfee58bd64 100644
>> >--- a/net/vmw_vsock/virtio_transport_common.c
>> >+++ b/net/vmw_vsock/virtio_transport_common.c
>> >@@ -447,7 +447,9 @@ static int virtio_transport_send_pkt_info(struct vsock_sock *vsk,
>> > static bool virtio_transport_inc_rx_pkt(struct virtio_vsock_sock *vvs,
>> >                                       u32 len)
>> > {
>> >-      if (vvs->buf_used + len > vvs->buf_alloc)
>> >+      u64 skb_overhead = (skb_queue_len(&vvs->rx_queue) + 1) * SKB_TRUESIZE(0);
>> >+
>> >+      if (skb_overhead + vvs->buf_used + len > vvs->buf_alloc)
>> >               return false;
>>
>> I'm not sure about this fix, I mean that maybe this is incomplete.
>> In virtio-vsock, there is a credit mechanism between the two peers:
>> https://docs.oasis-open.org/virtio/virtio/v1.3/csd01/virtio-v1.3-csd01.html#x1-4850003
>>
>> This takes only the payload into account, so it’s true that this problem
>> exists; however, perhaps we should also inform the other peer of a lower
>> credit balance, otherwise the other peer will believe it has much more
>> credit than it actually does, send a large payload, and then the packet
>> will be discarded and the data lost (there are no retransmissions,
>> etc.).
>
>I dunno, perhaps revert 077706165717 ("virtio/vsock: don't use skbuff
>state to account credit")
>and find a better fix then?

IIRC the same issue was there before the commit fixed by that one 
(commit 71dc9ec9ac7d ("virtio/vsock: replace virtio_vsock_pkt with 
sk_buff")), so not sure about reverting it TBH.

CCing Arseniy and Bobby.

>
>There is always a discrepancy between skb->len and skb->truesize.
>You will not be able to announce a 1MB window, and accept one milliion
>skb of 1-byte each.
>
>This kind of contract is broken.
>

Yep, I agree, but before we start discarding data (and losing it), IMHO 
we should at least inform the other peer that we're out of space.

@Stefan, @Michael, do you think we can do something in the spec to avoid 
this issue and in some way take into account also the metadata in the 
credit. I mean to avoid the 1-byte packets flooding.

Thanks,
Stefano

Re: [PATCH net] vsock/virtio: fix potential unbounded skb queue

[Bobby Eshleman]

On Tue, May 05, 2026 at 06:11:13PM +0200, Stefano Garzarella wrote:
> On Tue, May 05, 2026 at 07:14:36AM -0700, Eric Dumazet wrote:
> > On Tue, May 5, 2026 at 6:52 AM Stefano Garzarella <sgarzare@redhat.com> wrote:
> > > 
> > > On Thu, Apr 30, 2026 at 12:26:52PM +0000, Eric Dumazet wrote:
> > > >virtio_transport_inc_rx_pkt() checks vvs->rx_bytes + len > vvs->buf_alloc.
> > > >
> > > >virtio_transport_recv_enqueue() skips coalescing for packets
> > > >with VIRTIO_VSOCK_SEQ_EOM.
> > > >
> > > >If fed with packets with len == 0 and VIRTIO_VSOCK_SEQ_EOM,
> > > >a very large number of packets can be queued
> > > >because vvs->rx_bytes stays at 0.
> > > >
> > > >Fix this by estimating the skb metadata size:
> > > >
> > > >       (Number of skbs in the queue) * SKB_TRUESIZE(0)
> > > >
> > > >Fixes: 077706165717 ("virtio/vsock: don't use skbuff state to account credit")
> > > >Signed-off-by: Eric Dumazet <edumazet@google.com>
> > > >Cc: Arseniy Krasnov <AVKrasnov@sberdevices.ru>
> > > >Cc: Stefan Hajnoczi <stefanha@redhat.com>
> > > >Cc: Stefano Garzarella <sgarzare@redhat.com>
> > > >Cc: "Michael S. Tsirkin" <mst@redhat.com>
> > > >Cc: Jason Wang <jasowang@redhat.com>
> > > >Cc: Xuan Zhuo <xuanzhuo@linux.alibaba.com>
> > > >Cc: "Eugenio Pérez" <eperezma@redhat.com>
> > > >Cc: kvm@vger.kernel.org
> > > >Cc: virtualization@lists.linux.dev
> > > >---
> > > > net/vmw_vsock/virtio_transport_common.c | 4 +++-
> > > > 1 file changed, 3 insertions(+), 1 deletion(-)
> > > >
> > > >diff --git a/net/vmw_vsock/virtio_transport_common.c b/net/vmw_vsock/virtio_transport_common.c
> > > >index 416d533f493d7b07e9c77c43f741d28cfcd0953e..9b8014516f4fb1130ae184635fbba4dfee58bd64 100644
> > > >--- a/net/vmw_vsock/virtio_transport_common.c
> > > >+++ b/net/vmw_vsock/virtio_transport_common.c
> > > >@@ -447,7 +447,9 @@ static int virtio_transport_send_pkt_info(struct vsock_sock *vsk,
> > > > static bool virtio_transport_inc_rx_pkt(struct virtio_vsock_sock *vvs,
> > > >                                       u32 len)
> > > > {
> > > >-      if (vvs->buf_used + len > vvs->buf_alloc)
> > > >+      u64 skb_overhead = (skb_queue_len(&vvs->rx_queue) + 1) * SKB_TRUESIZE(0);
> > > >+
> > > >+      if (skb_overhead + vvs->buf_used + len > vvs->buf_alloc)
> > > >               return false;
> > > 
> > > I'm not sure about this fix, I mean that maybe this is incomplete.
> > > In virtio-vsock, there is a credit mechanism between the two peers:
> > > https://docs.oasis-open.org/virtio/virtio/v1.3/csd01/virtio-v1.3-csd01.html#x1-4850003
> > > 
> > > This takes only the payload into account, so it’s true that this problem
> > > exists; however, perhaps we should also inform the other peer of a lower
> > > credit balance, otherwise the other peer will believe it has much more
> > > credit than it actually does, send a large payload, and then the packet
> > > will be discarded and the data lost (there are no retransmissions,
> > > etc.).
> > 
> > I dunno, perhaps revert 077706165717 ("virtio/vsock: don't use skbuff
> > state to account credit")
> > and find a better fix then?
> 
> IIRC the same issue was there before the commit fixed by that one (commit
> 71dc9ec9ac7d ("virtio/vsock: replace virtio_vsock_pkt with sk_buff")), so
> not sure about reverting it TBH.
> 
> CCing Arseniy and Bobby.
> 
> > 
> > There is always a discrepancy between skb->len and skb->truesize.
> > You will not be able to announce a 1MB window, and accept one milliion
> > skb of 1-byte each.
> > 
> > This kind of contract is broken.
> > 
> 
> Yep, I agree, but before we start discarding data (and losing it), IMHO we
> should at least inform the other peer that we're out of space.
> 
> @Stefan, @Michael, do you think we can do something in the spec to avoid
> this issue and in some way take into account also the metadata in the
> credit. I mean to avoid the 1-byte packets flooding.
> 
> Thanks,
> Stefano
> 
> 

Indeed the old pre-fix skb code would have the same issue.

I can't think of any way around this without extending the spec.

Best,
Bobby