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[87.11.6.2]) by smtp.gmail.com with ESMTPSA id ffacd0b85a97d-45055f2487dsm4641869f8f.35.2026.05.05.06.51.55 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 05 May 2026 06:51:55 -0700 (PDT) Date: Tue, 5 May 2026 15:51:50 +0200 From: Stefano Garzarella To: Eric Dumazet Cc: "David S . Miller" , Jakub Kicinski , Paolo Abeni , Simon Horman , netdev@vger.kernel.org, eric.dumazet@gmail.com, Arseniy Krasnov , Stefan Hajnoczi , "Michael S. Tsirkin" , Jason Wang , Xuan Zhuo , Eugenio =?utf-8?B?UMOpcmV6?= , kvm@vger.kernel.org, virtualization@lists.linux.dev Subject: Re: [PATCH net] vsock/virtio: fix potential unbounded skb queue Message-ID: References: <20260430122653.554058-1-edumazet@google.com> Precedence: bulk X-Mailing-List: netdev@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8; format=flowed Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <20260430122653.554058-1-edumazet@google.com> 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 >Cc: Arseniy Krasnov >Cc: Stefan Hajnoczi >Cc: Stefano Garzarella >Cc: "Michael S. Tsirkin" >Cc: Jason Wang >Cc: Xuan Zhuo >Cc: "Eugenio Pérez" >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