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Tsirkin" , Jason Wang , =?UTF-8?q?Eugenio=20P=C3=A9rez?= Cc: Xuan Zhuo , "David S . Miller" , Eric Dumazet , Jakub Kicinski , Paolo Abeni , Simon Horman , kvm@vger.kernel.org, virtualization@lists.linux.dev, netdev@vger.kernel.org, linux-kernel@vger.kernel.org Subject: [PATCH v2] vsock: keep SOCK_SEQPACKET message boundaries on interrupted send Date: Sat, 19 Sep 2026 14:29:15 +0200 Message-ID: <20260919122916.28226-1-bartlomiej.dmitruk@isec.pl> X-Mailer: git-send-email 2.46.2 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 Content-Transfer-Encoding: 8bit A credit-limited SOCK_SEQPACKET send transmits fragments as credit becomes available, and the VIRTIO_VSOCK_SEQ_EOM flag is set only on the fragment where msg_data_left() reaches 0. If vsock_connectible_sendmsg() exits via out_err after a partial send -- notably the non-terminal -EINTR path (signal_pending while blocked for credit), but also sk_err / peer RCV_SHUTDOWN -- the already-transmitted fragments carry no EOM. The receiver only advances msg_count / sets msg_ready on an EOM skb, so the orphaned fragments are silently merged into the next message, violating SOCK_SEQPACKET atomicity. Wait until the whole remaining SEQPACKET message fits before enqueuing, so a message is committed atomically (with its EOM) or not started; an error while waiting then leaves nothing on the wire. SOCK_STREAM behaviour is unchanged (min_space == 1 reproduces the old "wait while space == 0"). To avoid blocking forever on a message that can never fit -- a peer can advertise a small buf_alloc, or the message can simply exceed the transmit buffer -- reject such a message up front with -EMSGSIZE (the same error the transport already returns for an oversized message) instead of waiting. This needs the transport's maximum message size, added as a new optional seqpacket_max_size() transport op implemented by the virtio/loopback transports. Signed-off-by: Bartłomiej Dmitruk Assisted-by: Claude (Anthropic) --- Changes in v2: - Fix an indefinite wait the v1 approach introduced for oversized SOCK_SEQPACKET messages (reported by the Sashiko AI review on v1): the atomic-wait could never be satisfied when len > the transport's max message size (e.g. a peer advertising a small peer_buf_alloc), so the sender blocked instead of returning -EMSGSIZE. v2 checks this up front via the new seqpacket_max_size() op and returns -EMSGSIZE without waiting. - v1: https://lore.kernel.org/netdev/20260917220101.55744-1-bartlomiej.dmitruk@isec.pl/ Testing (vsock_loopback, unprivileged): - Interrupted partial send (-EINTR) no longer leaks orphan bytes into the next message (recv() returns only the next message). - Oversized message and small-peer_buf_alloc cases return -EMSGSIZE promptly instead of blocking. - Normal SEQPACKET send/recv unaffected. diff --git a/include/linux/virtio_vsock.h b/include/linux/virtio_vsock.h index f91704731..e96790c03 100644 --- a/include/linux/virtio_vsock.h +++ b/include/linux/virtio_vsock.h @@ -219,6 +219,7 @@ virtio_transport_seqpacket_dequeue(struct vsock_sock *vsk, s64 virtio_transport_stream_has_data(struct vsock_sock *vsk); s64 virtio_transport_stream_has_space(struct vsock_sock *vsk); u32 virtio_transport_seqpacket_has_data(struct vsock_sock *vsk); +u32 virtio_transport_seqpacket_max_size(struct vsock_sock *vsk); ssize_t virtio_transport_unsent_bytes(struct vsock_sock *vsk); diff --git a/include/net/af_vsock.h b/include/net/af_vsock.h index 5549298c1..d94c613ef 100644 --- a/include/net/af_vsock.h +++ b/include/net/af_vsock.h @@ -143,6 +143,7 @@ struct vsock_transport { size_t len); bool (*seqpacket_allow)(struct vsock_sock *vsk, u32 remote_cid); u32 (*seqpacket_has_data)(struct vsock_sock *vsk); + u32 (*seqpacket_max_size)(struct vsock_sock *vsk); /* Notification. */ int (*notify_poll_in)(struct vsock_sock *, size_t, bool *); diff --git a/net/vmw_vsock/af_vsock.c b/net/vmw_vsock/af_vsock.c index f840498b5..ac64cb957 100644 --- a/net/vmw_vsock/af_vsock.c +++ b/net/vmw_vsock/af_vsock.c @@ -2250,9 +2250,32 @@ static int vsock_connectible_sendmsg(struct socket *sock, struct msghdr *msg, while (total_written < len) { ssize_t written; + s64 min_space; + + if (sk->sk_type == SOCK_SEQPACKET) { + /* A SEQPACKET message must be delivered atomically, so + * wait until the whole remaining message fits before + * enqueuing. Otherwise a credit-limited partial send that + * later errors out (e.g. -EINTR) leaves EOM-less fragments + * that the peer merges into the next message. + * + * Reject a message that can never fit up front so the wait + * below cannot block forever (a peer may advertise a small + * buf_alloc); this mirrors the -EMSGSIZE the transport + * returns for an oversized message. + */ + if (transport->seqpacket_max_size && + len > transport->seqpacket_max_size(vsk)) { + err = -EMSGSIZE; + goto out_err; + } + min_space = len - total_written; + } else { + min_space = 1; + } add_wait_queue(sk_sleep(sk), &wait); - while (vsock_stream_has_space(vsk) == 0 && + while (vsock_stream_has_space(vsk) < min_space && sk->sk_err == 0 && !(sk->sk_shutdown & SEND_SHUTDOWN) && !(vsk->peer_shutdown & RCV_SHUTDOWN)) { diff --git a/net/vmw_vsock/virtio_transport.c b/net/vmw_vsock/virtio_transport.c index 4f9aa9c4c..b7d587a20 100644 --- a/net/vmw_vsock/virtio_transport.c +++ b/net/vmw_vsock/virtio_transport.c @@ -585,6 +585,7 @@ static struct virtio_transport virtio_transport = { .seqpacket_enqueue = virtio_transport_seqpacket_enqueue, .seqpacket_allow = virtio_transport_seqpacket_allow, .seqpacket_has_data = virtio_transport_seqpacket_has_data, + .seqpacket_max_size = virtio_transport_seqpacket_max_size, .msgzerocopy_allow = virtio_transport_msgzerocopy_allow, diff --git a/net/vmw_vsock/virtio_transport_common.c b/net/vmw_vsock/virtio_transport_common.c index f225f53ed..e10e7b958 100644 --- a/net/vmw_vsock/virtio_transport_common.c +++ b/net/vmw_vsock/virtio_transport_common.c @@ -994,6 +994,19 @@ virtio_transport_seqpacket_enqueue(struct vsock_sock *vsk, } EXPORT_SYMBOL_GPL(virtio_transport_seqpacket_enqueue); +u32 virtio_transport_seqpacket_max_size(struct vsock_sock *vsk) +{ + struct virtio_vsock_sock *vvs = vsk->trans; + u32 max_size; + + spin_lock_bh(&vvs->tx_lock); + max_size = virtio_transport_tx_buf_size(vvs); + spin_unlock_bh(&vvs->tx_lock); + + return max_size; +} +EXPORT_SYMBOL_GPL(virtio_transport_seqpacket_max_size); + int virtio_transport_dgram_dequeue(struct vsock_sock *vsk, struct msghdr *msg, diff --git a/net/vmw_vsock/vsock_loopback.c b/net/vmw_vsock/vsock_loopback.c index 8068d1b6e..b9a0cc861 100644 --- a/net/vmw_vsock/vsock_loopback.c +++ b/net/vmw_vsock/vsock_loopback.c @@ -90,6 +90,7 @@ static struct virtio_transport loopback_transport = { .seqpacket_enqueue = virtio_transport_seqpacket_enqueue, .seqpacket_allow = vsock_loopback_seqpacket_allow, .seqpacket_has_data = virtio_transport_seqpacket_has_data, + .seqpacket_max_size = virtio_transport_seqpacket_max_size, .msgzerocopy_allow = vsock_loopback_msgzerocopy_allow,