Merge branch 'vsock-virtio-fix-data-loss-disclosure-due-to-joining-of-non-linear-skb'

Michal Luczaj says:

====================
vsock/virtio: Fix data loss/disclosure due to joining of non-linear skb

Loopback transport coalesces some skbs too eagerly. Handling a zerocopy
(non-linear) skb as a linear one leads to skb data loss and kernel memory
disclosure.

Plug the loss/leak by allowing only linear skb join. Provide a test.
====================

Link: https://patch.msgid.link/20260113-vsock-recv-coalescence-v2-0-552b17837cf4@rbox.co
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

Author: kuba-moo

net/vmw_vsock/virtio_transport_common.c

@@ -1359,9 +1359,11 @@ virtio_transport_recv_enqueue(struct vsock_sock *vsk,
 
 	/* Try to copy small packets into the buffer of last packet queued,
 	 * to avoid wasting memory queueing the entire buffer with a small
-	 * payload.
+	 * payload. Skip non-linear (e.g. zerocopy) skbs; these carry payload
+	 * in skb_shinfo.
 	 */
-	if (len <= GOOD_COPY_LEN && !skb_queue_empty(&vvs->rx_queue)) {
+	if (len <= GOOD_COPY_LEN && !skb_queue_empty(&vvs->rx_queue) &&
+	    !skb_is_nonlinear(skb)) {
 		struct virtio_vsock_hdr *last_hdr;
 		struct sk_buff *last_skb;
 

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 virtio MSG_ZEROCOPY coalescence corruption",
+		.run_client = test_stream_msgzcopy_mangle_client,
+		.run_server = test_stream_msgzcopy_mangle_server,
+	},
 	{},
 };
 

tools/testing/vsock/vsock_test_zerocopy.c

@@ -9,14 +9,18 @@
 #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 <linux/time64.h>
 #include <errno.h>
 
 #include "control.h"
+#include "timeout.h"
 #include "vsock_test_zerocopy.h"
 #include "msg_zerocopy_common.h"
 
@@ -356,3 +360,73 @@ 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];
+	unsigned long hash;
+	struct pollfd fds;
+	int fd, i;
+
+	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, 'x', sizeof(sbuf1));
+	send_buf(fd, sbuf1, sizeof(sbuf1), 0, sizeof(sbuf1));
+
+	for (i = 0; i < sizeof(sbuf2); i++)
+		sbuf2[i] = rand() & 0xff;
+
+	send_buf(fd, sbuf2, sizeof(sbuf2), MSG_ZEROCOPY, sizeof(sbuf2));
+
+	hash = hash_djb2(sbuf2, sizeof(sbuf2));
+	control_writeulong(hash);
+
+	fds.fd = fd;
+	fds.events = 0;
+
+	if (poll(&fds, 1, TIMEOUT * MSEC_PER_SEC) != 1 ||
+	    !(fds.revents & POLLERR)) {
+		perror("poll");
+		exit(EXIT_FAILURE);
+	}
+
+	close(fd);
+}
+
+void test_stream_msgzcopy_mangle_server(const struct test_opts *opts)
+{
+	unsigned long local_hash, remote_hash;
+	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);
+
+	/* Discard the first packet. */
+	recv_buf(fd, rbuf, PAGE_SIZE + 1, 0, PAGE_SIZE + 1);
+
+	recv_buf(fd, rbuf, GOOD_COPY_LEN, 0, GOOD_COPY_LEN);
+	remote_hash = control_readulong();
+	local_hash = hash_djb2(rbuf, GOOD_COPY_LEN);
+
+	if (local_hash != remote_hash) {
+		fprintf(stderr, "Data received corrupted\n");
+		exit(EXIT_FAILURE);
+	}
+
+	close(fd);
+}

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 */