[PATCH net-next 2/2] vsock/test: Add test for null ptr deref when transport changes

[Luigi Leonardi <leonardi@redhat.com>]

Add a new test to ensure that when the transport changes a null pointer
dereference does not occur[1].

Note that this test does not fail, but it may hang on the client side if
it triggers a kernel oops.

This works by creating a socket, trying to connect to a server, and then
executing a second connect operation on the same socket but to a
different CID (0). This triggers a transport change. If the connect
operation is interrupted by a signal, this could cause a null-ptr-deref.

Since this bug is non-deterministic, we need to try several times. It
is safe to assume that the bug will show up within the timeout period.

If there is a G2H transport loaded in the system, the bug is not
triggered and this test will always pass.

[1]https://lore.kernel.org/netdev/Z2LvdTTQR7dBmPb5@v4bel-B760M-AORUS-ELITE-AX/

Suggested-by: Michal Luczaj <mhal@rbox.co>
Signed-off-by: Luigi Leonardi <leonardi@redhat.com>
---
 tools/testing/vsock/Makefile     |  1 +
 tools/testing/vsock/vsock_test.c | 80 ++++++++++++++++++++++++++++++++++++++++
 2 files changed, 81 insertions(+)

diff --git a/tools/testing/vsock/Makefile b/tools/testing/vsock/Makefile
index 6e0b4e95e230500f99bb9c74350701a037ecd198..88211fd132d23ecdfd56ab0815580a237889e7f2 100644
--- a/tools/testing/vsock/Makefile
+++ b/tools/testing/vsock/Makefile
@@ -5,6 +5,7 @@ vsock_test: vsock_test.o vsock_test_zerocopy.o timeout.o control.o util.o msg_ze
 vsock_diag_test: vsock_diag_test.o timeout.o control.o util.o
 vsock_perf: vsock_perf.o msg_zerocopy_common.o
 
+vsock_test: LDLIBS = -lpthread
 vsock_uring_test: LDLIBS = -luring
 vsock_uring_test: control.o util.o vsock_uring_test.o timeout.o msg_zerocopy_common.o
 
diff --git a/tools/testing/vsock/vsock_test.c b/tools/testing/vsock/vsock_test.c
index d0f6d253ac72d08a957cb81a3c38fcc72bec5a53..1e00cb6e117859d5c18fb3e52a574444b5489173 100644
--- a/tools/testing/vsock/vsock_test.c
+++ b/tools/testing/vsock/vsock_test.c
@@ -23,6 +23,7 @@
 #include <sys/ioctl.h>
 #include <linux/sockios.h>
 #include <linux/time64.h>
+#include <pthread.h>
 
 #include "vsock_test_zerocopy.h"
 #include "timeout.h"
@@ -1788,6 +1789,80 @@ static void test_stream_connect_retry_server(const struct test_opts *opts)
 	close(fd);
 }
 
+static void *test_transport_change_thread(void *vargp)
+{
+	pid_t *t = (pid_t *)vargp;
+
+	//We want this thread to terminate as soon as possible
+	pthread_setcanceltype(PTHREAD_CANCEL_ASYNCHRONOUS, NULL);
+
+	while (true)
+		kill(*t, SIGUSR1);
+	return NULL;
+}
+
+static void test_transport_change_signal_handler(int signal)
+{
+}
+
+static void test_transport_change_client(const struct test_opts *opts)
+{
+	__sighandler_t old_handler;
+	pid_t pid = getpid();
+	pthread_t thread_id;
+
+	old_handler = signal(SIGUSR1, test_transport_change_signal_handler);
+
+	pthread_create(&thread_id, NULL, test_transport_change_thread, &pid);
+
+	timeout_begin(TIMEOUT);
+
+	while (true) {
+		struct sockaddr_vm sa = {
+			.svm_family = AF_VSOCK,
+			.svm_cid = opts->peer_cid,
+			.svm_port = opts->peer_port,
+		};
+
+		int s = socket(AF_VSOCK, SOCK_STREAM, 0);
+
+		connect(s, (struct sockaddr *)&sa, sizeof(sa));
+
+		sa.svm_cid = 0;
+		connect(s, (struct sockaddr *)&sa, sizeof(sa));
+
+		close(s);
+
+		if (timeout_check_expired())
+			break;
+	}
+
+	timeout_end();
+
+	pthread_cancel(thread_id);
+	//Wait for the thread to terminate
+	pthread_join(thread_id, NULL);
+	//Restore the old handler
+	signal(SIGUSR1, old_handler);
+}
+
+static void test_transport_change_server(const struct test_opts *opts)
+{
+	timeout_begin(TIMEOUT);
+
+	while (true) {
+		int s;
+
+		s = vsock_stream_listen(opts->peer_cid, opts->peer_port);
+		close(s);
+
+		if (timeout_check_expired())
+			break;
+	}
+
+	timeout_end();
+}
+
 static void test_stream_linger_client(const struct test_opts *opts)
 {
 	struct linger optval = {
@@ -1984,6 +2059,11 @@ static struct test_case test_cases[] = {
 		.run_client = test_stream_linger_client,
 		.run_server = test_stream_linger_server,
 	},
+	{
+		.name = "SOCK_STREAM transport change null-ptr-deref",
+		.run_client = test_transport_change_client,
+		.run_server = test_transport_change_server,
+	},
 	{},
 };
 

-- 
2.48.1