linux-kernel - Re: [PATCH net-next v2] vsock/test: Add test for null ptr deref when transport changes

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <qp67w36nyzgyd45wi7oosxe6syx7dzcifc5s2eg47engirtrnf@ewnk6ngqw7h3>
Date: Wed, 26 Mar 2025 17:21:03 +0100
From: Stefano Garzarella <sgarzare@...hat.com>
To: Luigi Leonardi <leonardi@...hat.com>
Cc: Michal Luczaj <mhal@...x.co>, virtualization@...ts.linux.dev, 
	netdev@...r.kernel.org, linux-kernel@...r.kernel.org, Hyunwoo Kim <v4bel@...ori.io>
Subject: Re: [PATCH net-next v2] vsock/test: Add test for null ptr deref when
 transport changes

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