On Wed, Mar 26, 2025 at 04:14:20PM +0100, Luigi Leonardi wrote:
Hi Michal,
On Wed, Mar 19, 2025 at 01:27:35AM +0100, Michal Luczaj wrote:
On 3/14/25 10:27, Luigi Leonardi wrote:
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.
Just to be clear: that's the splat, right?
Oops: general protection fault, probably for non-canonical address
0xdffffc000000000c: 0000 [#1] PREEMPT SMP KASAN NOPTI
KASAN: null-ptr-deref in range [0x0000000000000060-0x0000000000000067]
CPU: 2 UID: 0 PID: 463 Comm: kworker/2:3 Not tainted
Workqueue: vsock-loopback vsock_loopback_work
RIP: 0010:vsock_stream_has_data+0x44/0x70
Call Trace:
virtio_transport_do_close+0x68/0x1a0
virtio_transport_recv_pkt+0x1045/0x2ae4
vsock_loopback_work+0x27d/0x3f0
process_one_work+0x846/0x1420
worker_thread+0x5b3/0xf80
kthread+0x35a/0x700
ret_from_fork+0x2d/0x70
ret_from_fork_asm+0x1a/0x30
Yep! I'll add it to the commit message in v3.
...
+static void test_stream_transport_change_client(const struct test_opts *opts)
+{
+ __sighandler_t old_handler;
+ pid_t pid = getpid();
+ pthread_t thread_id;
+ time_t tout;
+
+ old_handler = signal(SIGUSR1, test_transport_change_signal_handler);
+ if (old_handler == SIG_ERR) {
+ perror("signal");
+ exit(EXIT_FAILURE);
+ }
+
+ if (pthread_create(&thread_id, NULL, test_stream_transport_change_thread,
&pid)) {
+ perror("pthread_create");
Does pthread_create() set errno on failure?
It does not, very good catch!
+ exit(EXIT_FAILURE);
+ }
+
+ tout = current_nsec() + TIMEOUT * NSEC_PER_SEC;
Isn't 10 seconds a bit excessive? I see the oops pretty much immediately.
Yeah it's probably excessive. I used because it's the default timeout
value.
+ do {
+ struct sockaddr_vm sa = {
+ .svm_family = AF_VSOCK,
+ .svm_cid = opts->peer_cid,
+ .svm_port = opts->peer_port,
+ };
+ int s;
+
+ s = socket(AF_VSOCK, SOCK_STREAM, 0);
+ if (s < 0) {
+ perror("socket");
+ exit(EXIT_FAILURE);
+ }
+
+ connect(s, (struct sockaddr *)&sa, sizeof(sa));
+
+ /* Set CID to 0 cause a transport change. */
+ sa.svm_cid = 0;
+ connect(s, (struct sockaddr *)&sa, sizeof(sa));
+
+ close(s);
+ } while (current_nsec() < tout);
+
+ if (pthread_cancel(thread_id)) {
+ perror("pthread_cancel");
And errno here.
+ exit(EXIT_FAILURE);
+ }
+
+ /* Wait for the thread to terminate */
+ if (pthread_join(thread_id, NULL)) {
+ perror("pthread_join");
And here.
Aaand I've realized I've made exactly the same mistake elsewhere :)
...
+static void test_stream_transport_change_server(const struct test_opts *opts)
+{
+ time_t tout = current_nsec() + TIMEOUT * NSEC_PER_SEC;
+
+ do {
+ int s = vsock_stream_listen(VMADDR_CID_ANY, opts->peer_port);
+
+ close(s);
+ } while (current_nsec() < tout);
+}
I'm not certain you need to re-create the listener or measure the time
here. What about something like
int s = vsock_stream_listen(VMADDR_CID_ANY, opts->peer_port);
control_expectln("DONE");
close(s);
Just tried and it triggers the oops :)
If this works (as I also initially thought), we should check the result
of the first connect() in the client code. It can succeed or fail with
-EINTR, in other cases we should report an error because it is not
expected.
And we should check also the second connect(), it should always fail,
right?
For this I think you need another sync point to be sure the server is
listening before try to connect the first time:
client:
// pthread_create, etc.
control_expectln("LISTENING");
do {
...
} while();
control_writeln("DONE");
server:
int s = vsock_stream_listen(VMADDR_CID_ANY, opts->peer_port);
control_writeln("LISTENING");
control_expectln("DONE");
close(s);
Thanks,
Stefano
