Add a new test to ensure that when the transport changes a null pointer
dereference does not occur. The bug was reported upstream [1] and fixed
with commit 2cb7c756f605 ("vsock/virtio: discard packets if the
transport changes").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 Note that this test may not fail in a kernel without the fix, 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 reasonable 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: Hyunwoo Kim <v4...@theori.io> Suggested-by: Michal Luczaj <m...@rbox.co> Signed-off-by: Luigi Leonardi <leona...@redhat.com> --- This series introduces a new test that checks for a null pointer dereference that may happen when there is a transport change[1]. This bug was fixed in [2]. Note that this test *cannot* fail, it hangs if it triggers a kernel oops. The intended use-case is to run it and then check if there is any oops in the dmesg. This test is based on Hyunwoo Kim's[3] and Michal's python reproducers[4]. [1]https://lore.kernel.org/netdev/Z2LvdTTQR7dBmPb5@v4bel-B760M-AORUS-ELITE-AX/ [2]https://lore.kernel.org/netdev/20250110083511.30419-1-sgarz...@redhat.com/ [3]https://lore.kernel.org/netdev/Z2LvdTTQR7dBmPb5@v4bel-B760M-AORUS-ELITE-AX/#t [4]https://lore.kernel.org/netdev/2b3062e3-bdaa-4c94-a3c0-2930595b9...@rbox.co/ --- Changes in v4: - Addressed Stefano's comments: - Minor style changes - Use `get_transports()` to print a warning when a G2H transport is loaded - Removed check on second connect: Because the first connect is interrupted, the socket is in an unspecified state (see man connect) . This can cause strange and unexpected behaviors (connect returning success on a non-existing CID). - Link to v3: https://lore.kernel.org/r/20250611-test_vsock-v3-1-8414a2d4d...@redhat.com Sorry, this took waaay longer than expected. Changes in v3: Addressed Stefano's and Michal's comments: - Added the splat text to the commit commessage. - Introduced commit hash that fixes the bug. - Not using perror anymore on pthread_* functions. - Listener is just created once. - Link to v2: https://lore.kernel.org/r/20250314-test_vsock-v2-1-3c0a1d878...@redhat.com Changes in v2: - Addressed Stefano's comments: - Timeout is now using current_nsec() - Check for return values - Style issues - Added Hyunwoo Kim to Suggested-by - Link to v1: https://lore.kernel.org/r/20250306-test_vsock-v1-0-0320b5acc...@redhat.com --- tools/testing/vsock/Makefile | 1 + tools/testing/vsock/vsock_test.c | 178 +++++++++++++++++++++++++++++++++++++++ 2 files changed, 179 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 eb6f54378667ac7ed324f4823e988ec9846e41a3..095705c7b53b7ad38ab3b8bc3cbe54a9eeb76d5c 100644 --- a/tools/testing/vsock/vsock_test.c +++ b/tools/testing/vsock/vsock_test.c @@ -22,6 +22,8 @@ #include <signal.h> #include <sys/ioctl.h> #include <linux/time64.h> +#include <pthread.h> +#include <fcntl.h> #include "vsock_test_zerocopy.h" #include "timeout.h" @@ -1867,6 +1869,177 @@ static void test_stream_connect_retry_server(const struct test_opts *opts) close(fd); } +#define TRANSPORT_CHANGE_TIMEOUT 2 /* seconds */ + +static void *test_stream_transport_change_thread(void *vargp) +{ + pid_t *pid = (pid_t *)vargp; + int ret; + + /* We want this thread to terminate as soon as possible */ + ret = pthread_setcanceltype(PTHREAD_CANCEL_ASYNCHRONOUS, NULL); + if (ret) { + fprintf(stderr, "pthread_setcanceltype: %d\n", ret); + exit(EXIT_FAILURE); + } + + while (true) { + if (kill(*pid, SIGUSR1) < 0) { + perror("kill"); + exit(EXIT_FAILURE); + } + } + return NULL; +} + +static void test_transport_change_signal_handler(int signal) +{ + /* We need a custom handler for SIGUSR1 as the default one terminates the process. */ +} + +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; + int ret, tr; + + tr = get_transports(); + /* Print a warning if there is a G2H transport loaded. + * This is on a best effort basis because VMCI can be either G2H and H2G, and there is + * no easy way to understand it. + * The bug is present in the loopback transport. However, it does not interfere + * if it is loaded. + * The bug we are testing only appears when G2H transports are not loaded. + */ + + tr &= ~TRANSPORT_LOOPBACK; + if (tr != 0 && tr != TRANSPORT_VHOST) + fprintf(stderr, "G2H Transport detected. This test will not fail.\n"); + + old_handler = signal(SIGUSR1, test_transport_change_signal_handler); + if (old_handler == SIG_ERR) { + perror("signal"); + exit(EXIT_FAILURE); + } + + ret = pthread_create(&thread_id, NULL, test_stream_transport_change_thread, &pid); + if (ret) { + fprintf(stderr, "pthread_create: %d\n", ret); + exit(EXIT_FAILURE); + } + + control_expectln("LISTENING"); + + tout = current_nsec() + TRANSPORT_CHANGE_TIMEOUT * NSEC_PER_SEC; + 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); + } + + ret = connect(s, (struct sockaddr *)&sa, sizeof(sa)); + /* The connect can fail due to signals coming from the thread. + * or because the receiver connection queue is full. + * Ignoring also the latter case because there is no way + * of synchronizing client's connect and server's accept when + * connect(s) are constantly being interrupted by signals. + */ + if (ret == -1 && (errno != EINTR && errno != ECONNRESET)) { + perror("connect"); + exit(EXIT_FAILURE); + } + + /* Set CID to 0 cause a transport change. */ + sa.svm_cid = 0; + /* Here we ignore the connect return value because we cannot + * safely assume that it will *always* fail. + * This is because the previous connect was interrupted + * during the connection process. The socket state, as stated + * in `man connect`, is unspecified and can result in strange + * behaviors. + */ + connect(s, (struct sockaddr *)&sa, sizeof(sa)); + + close(s); + + control_writeulong(CONTROL_CONTINUE); + + } while (current_nsec() < tout); + + control_writeulong(CONTROL_DONE); + + ret = pthread_cancel(thread_id); + if (ret) { + fprintf(stderr, "pthread_cancel: %d\n", ret); + exit(EXIT_FAILURE); + } + + /* Wait for the thread to terminate */ + ret = pthread_join(thread_id, NULL); + if (ret) { + fprintf(stderr, "pthread_join: %d\n", ret); + exit(EXIT_FAILURE); + } + + /* Restore the old handler */ + if (signal(SIGUSR1, old_handler) == SIG_ERR) { + perror("signal"); + exit(EXIT_FAILURE); + } +} + +static void test_stream_transport_change_server(const struct test_opts *opts) +{ + int s = vsock_stream_listen(VMADDR_CID_ANY, opts->peer_port); + + /* Set the socket to be nonblocking because connects that have been interrupted + * (EINTR) can fill the receiver's accept queue anyway, leading to connect failure. + * As of today (6.15) in such situation there is no way to understand, from the + * client side, if the connection has been queued in the server or not. + */ + if (fcntl(s, F_SETFL, fcntl(s, F_GETFL, 0) | O_NONBLOCK) < 0) { + perror("fcntl"); + exit(EXIT_FAILURE); + } + control_writeln("LISTENING"); + + while (control_readulong() == CONTROL_CONTINUE) { + struct sockaddr_vm sa_client; + socklen_t socklen_client = sizeof(sa_client); + + /* Must accept the connection, otherwise the `listen` + * queue will fill up and new connections will fail. + * There can be more than one queued connection, + * clear them all. + */ + while (true) { + int client = accept(s, (struct sockaddr *)&sa_client, &socklen_client); + + if (client < 0) { + if (errno == EAGAIN) + break; + + perror("accept"); + exit(EXIT_FAILURE); + } + + close(client); + } + } + + close(s); +} + static void test_stream_linger_client(const struct test_opts *opts) { int fd; @@ -2106,6 +2279,11 @@ static struct test_case test_cases[] = { .run_client = test_stream_nolinger_client, .run_server = test_stream_nolinger_server, }, + { + .name = "SOCK_STREAM transport change null-ptr-deref", + .run_client = test_stream_transport_change_client, + .run_server = test_stream_transport_change_server, + }, {}, }; --- base-commit: 68d019aa14d97f8d57b0f8d203fd3b44db2ba0c7 change-id: 20250306-test_vsock-3e77a9c7a245 Best regards, -- Luigi Leonardi <leona...@redhat.com>
