linux-kernel - [PATCH 2/2] vsock/test: Add test for a linear and non-linear skb getting coalesced

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Message-Id: <20260108-vsock-recv-coalescence-v1-2-26f97bb9a99b@rbox.co>
Date: Thu, 08 Jan 2026 10:54:55 +0100
From: Michal Luczaj <mhal@...x.co>
To: "Michael S. Tsirkin" <mst@...hat.com>, Jason Wang <jasowang@...hat.com>, 
 Xuan Zhuo <xuanzhuo@...ux.alibaba.com>, 
 Eugenio Pérez <eperezma@...hat.com>, 
 Stefan Hajnoczi <stefanha@...hat.com>, 
 Stefano Garzarella <sgarzare@...hat.com>, 
 "David S. Miller" <davem@...emloft.net>, Eric Dumazet <edumazet@...gle.com>, 
 Jakub Kicinski <kuba@...nel.org>, Paolo Abeni <pabeni@...hat.com>, 
 Simon Horman <horms@...nel.org>, 
 Arseniy Krasnov <avkrasnov@...utedevices.com>
Cc: kvm@...r.kernel.org, virtualization@...ts.linux.dev, 
 netdev@...r.kernel.org, linux-kernel@...r.kernel.org, 
 Michal Luczaj <mhal@...x.co>
Subject: [PATCH 2/2] vsock/test: Add test for a linear and non-linear skb
 getting coalesced

Loopback transport can mangle data in rx queue when a linear skb is
followed by a small MSG_ZEROCOPY packet.

Signed-off-by: Michal Luczaj <mhal@...x.co>
---
 tools/testing/vsock/vsock_test.c          |  5 +++
 tools/testing/vsock/vsock_test_zerocopy.c | 67 +++++++++++++++++++++++++++++++
 tools/testing/vsock/vsock_test_zerocopy.h |  3 ++
 3 files changed, 75 insertions(+)

diff --git a/tools/testing/vsock/vsock_test.c b/tools/testing/vsock/vsock_test.c
index bbe3723babdc..21c8616100f1 100644
--- a/tools/testing/vsock/vsock_test.c
+++ b/tools/testing/vsock/vsock_test.c
@@ -2403,6 +2403,11 @@ static struct test_case test_cases[] = {
 		.run_client = test_stream_accepted_setsockopt_client,
 		.run_server = test_stream_accepted_setsockopt_server,
 	},
+	{
+		.name = "SOCK_STREAM MSG_ZEROCOPY coalescence corruption",
+		.run_client = test_stream_msgzcopy_mangle_client,
+		.run_server = test_stream_msgzcopy_mangle_server,
+	},
 	{},
 };
 
diff --git a/tools/testing/vsock/vsock_test_zerocopy.c b/tools/testing/vsock/vsock_test_zerocopy.c
index 9d9a6cb9614a..6735a9d7525d 100644
--- a/tools/testing/vsock/vsock_test_zerocopy.c
+++ b/tools/testing/vsock/vsock_test_zerocopy.c
@@ -9,11 +9,13 @@
 #include <stdio.h>
 #include <stdlib.h>
 #include <string.h>
+#include <sys/ioctl.h>
 #include <sys/mman.h>
 #include <unistd.h>
 #include <poll.h>
 #include <linux/errqueue.h>
 #include <linux/kernel.h>
+#include <linux/sockios.h>
 #include <errno.h>
 
 #include "control.h"
@@ -356,3 +358,68 @@ void test_stream_msgzcopy_empty_errq_server(const struct test_opts *opts)
 	control_expectln("DONE");
 	close(fd);
 }
+
+#define GOOD_COPY_LEN	128	/* net/vmw_vsock/virtio_transport_common.c */
+
+void test_stream_msgzcopy_mangle_client(const struct test_opts *opts)
+{
+	char sbuf1[PAGE_SIZE + 1], sbuf2[GOOD_COPY_LEN];
+	struct pollfd fds;
+	int fd;
+
+	fd = vsock_stream_connect(opts->peer_cid, opts->peer_port);
+	if (fd < 0) {
+		perror("connect");
+		exit(EXIT_FAILURE);
+	}
+
+	enable_so_zerocopy_check(fd);
+
+	memset(sbuf1, '1', sizeof(sbuf1));
+	memset(sbuf2, '2', sizeof(sbuf2));
+
+	send_buf(fd, sbuf1, sizeof(sbuf1), 0, sizeof(sbuf1));
+	send_buf(fd, sbuf2, sizeof(sbuf2), MSG_ZEROCOPY, sizeof(sbuf2));
+
+	fds.fd = fd;
+	fds.events = 0;
+
+	if (poll(&fds, 1, -1) != 1 || !(fds.revents & POLLERR)) {
+		perror("poll");
+		exit(EXIT_FAILURE);
+	}
+
+	close(fd);
+}
+
+static void recv_verify(int fd, char *buf, unsigned int len, char pattern)
+{
+	recv_buf(fd, buf, len, 0, len);
+
+	while (len--) {
+		if (*buf++ != pattern) {
+			fprintf(stderr, "Incorrect data received\n");
+			exit(EXIT_FAILURE);
+		}
+	}
+}
+
+void test_stream_msgzcopy_mangle_server(const struct test_opts *opts)
+{
+	char rbuf[PAGE_SIZE + 1];
+	int fd;
+
+	fd = vsock_stream_accept(VMADDR_CID_ANY, opts->peer_port, NULL);
+	if (fd < 0) {
+		perror("accept");
+		exit(EXIT_FAILURE);
+	}
+
+	/* Wait, don't race the (buggy) skbs coalescence. */
+	vsock_ioctl_int(fd, SIOCINQ, PAGE_SIZE + 1 + GOOD_COPY_LEN);
+
+	recv_verify(fd, rbuf, PAGE_SIZE + 1, '1');
+	recv_verify(fd, rbuf, GOOD_COPY_LEN, '2');
+
+	close(fd);
+}
diff --git a/tools/testing/vsock/vsock_test_zerocopy.h b/tools/testing/vsock/vsock_test_zerocopy.h
index 3ef2579e024d..d46c91a69f16 100644
--- a/tools/testing/vsock/vsock_test_zerocopy.h
+++ b/tools/testing/vsock/vsock_test_zerocopy.h
@@ -12,4 +12,7 @@ void test_seqpacket_msgzcopy_server(const struct test_opts *opts);
 void test_stream_msgzcopy_empty_errq_client(const struct test_opts *opts);
 void test_stream_msgzcopy_empty_errq_server(const struct test_opts *opts);
 
+void test_stream_msgzcopy_mangle_client(const struct test_opts *opts);
+void test_stream_msgzcopy_mangle_server(const struct test_opts *opts);
+
 #endif /* VSOCK_TEST_ZEROCOPY_H */

-- 
2.52.0