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[87.16.204.231]) by smtp.gmail.com with ESMTPSA id ffacd0b85a97d-454917d57aesm40237869f8f.26.2026.05.13.03.54.28 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 13 May 2026 03:54:29 -0700 (PDT) From: Stefano Garzarella To: netdev@vger.kernel.org Cc: Xuan Zhuo , "Michael S. Tsirkin" , =?UTF-8?q?Eugenio=20P=C3=A9rez?= , linux-kernel@vger.kernel.org, Simon Horman , Paolo Abeni , Jakub Kicinski , Stefano Garzarella , Jason Wang , kvm@vger.kernel.org, Stefan Hajnoczi , virtualization@lists.linux.dev, Eric Dumazet , "David S. Miller" Subject: [PATCH net v3 2/2] vsock/virtio: fix skb overhead accounting to preserve full buf_alloc Date: Wed, 13 May 2026 12:54:17 +0200 Message-ID: <20260513105417.56761-3-sgarzare@redhat.com> X-Mailer: git-send-email 2.54.0 In-Reply-To: <20260513105417.56761-1-sgarzare@redhat.com> References: <20260513105417.56761-1-sgarzare@redhat.com> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit From: Stefano Garzarella After commit 059b7dbd20a6 ("vsock/virtio: fix potential unbounded skb queue"), virtio_transport_inc_rx_pkt() subtracts per-skb overhead from buf_alloc when checking whether a new packet fits. This reduces the effective receive buffer below what the user configured via SO_VM_SOCKETS_BUFFER_SIZE, causing legitimate data packets to be silently dropped and applications that rely on the full buffer size to deadlock. Also, the reduced space is not communicated to the remote peer, so its credit calculation accounts more credit than the receiver will actually accept, causing data loss (there is no retransmission). With this approach we currently have failures in tools/testing/vsock/vsock_test.c. Test 18 sometimes fails, while test 22 always fails in this way: 18 - SOCK_STREAM MSG_ZEROCOPY...hash mismatch 22 - SOCK_STREAM virtio credit update + SO_RCVLOWAT...send failed: Resource temporarily unavailable Fix this by using `buf_alloc * 2` as the total budget for payload plus skb overhead in virtio_transport_inc_rx_pkt(), similar to how SO_RCVBUF is doubled to reserve space for sk_buff metadata. This preserves the full buf_alloc for payload under normal operation, while still bounding the skb queue growth. With this patch, all tests in tools/testing/vsock/vsock_test.c are now passing again. Fixes: 059b7dbd20a6 ("vsock/virtio: fix potential unbounded skb queue") Signed-off-by: Stefano Garzarella --- net/vmw_vsock/virtio_transport_common.c | 5 ++++- 1 file changed, 4 insertions(+), 1 deletion(-) diff --git a/net/vmw_vsock/virtio_transport_common.c b/net/vmw_vsock/virtio_transport_common.c index 4a4ac69d1ad1..e22117bf5dcd 100644 --- a/net/vmw_vsock/virtio_transport_common.c +++ b/net/vmw_vsock/virtio_transport_common.c @@ -434,7 +434,10 @@ static bool virtio_transport_inc_rx_pkt(struct virtio_vsock_sock *vvs, { u64 skb_overhead = (skb_queue_len(&vvs->rx_queue) + 1) * SKB_TRUESIZE(0); - if (skb_overhead + vvs->buf_used + len > vvs->buf_alloc) + /* Use buf_alloc * 2 as total budget (payload + overhead), similar to + * how SO_RCVBUF is doubled to reserve space for sk_buff metadata. + */ + if (skb_overhead + vvs->buf_used + len > (u64)vvs->buf_alloc * 2) return false; vvs->rx_bytes += len; -- 2.54.0