[Devel] [PATCH hci-8.1 v6 2/2] selftests: ve: introduce vtty pair teardown stress test
Eva Kurchatova
eva.kurchatova at virtuozzo.com
Fri Oct 2 07:43:14 MSK 2026
Either end of a vtty pair creates it, and the last close tears it down.
Race condition in older VZKernel vtty implementation allowed both sides
to decide they were the final one and call release_tty() twice, and a
master opening again while a teardown was in flight used to hand out a
reference to a tty_struct about to be freed. Either way, this caused
use-after-free. That issue was fixed in c5028cd61a69:
"ve/vtty: fix use-after-free on concurrent tty close and reopen"
Hammer both ends for ownership correctness & thread safety verification.
The original reproducer needed a few tens of minutes across a dozen
containers, where vzctl interaction with vtty subsystem was a small part
of the overall runtime, therefore it did not fire on every run. This test
opens and closes nothing but the pair, from both ends and without pause,
so the default stays in the tens of seconds and under the timeout of the
suite, and VE_VTTY_SECS or argv[1] allows to control this.
ve_id_write() does not check that a veid is unique and the vtty map is
keyed by veid, so a clash would hand the test a running container's
pair. Before writing ve.veid the test asks the kernel, through the
vzctl ioctl, whether the veid is taken, and skips when it is. It also
skips where /tmp is mounted nodev: mknod() succeeds there and every
open of the slave node fails.
https://virtuozzo.atlassian.net/browse/VSTOR-144771
Feature: ve selftest
Signed-off-by: Eva Kurchatova <eva.kurchatova at virtuozzo.com>
---
tools/testing/selftests/ve/.gitignore | 1 +
tools/testing/selftests/ve/Makefile | 3 +-
tools/testing/selftests/ve/ve_vtty_stress.c | 343 ++++++++++++++++++++
3 files changed, 346 insertions(+), 1 deletion(-)
create mode 100644 tools/testing/selftests/ve/ve_vtty_stress.c
diff --git a/tools/testing/selftests/ve/.gitignore b/tools/testing/selftests/ve/.gitignore
index 3df4d05888dc..d8eb5c346c6e 100644
--- a/tools/testing/selftests/ve/.gitignore
+++ b/tools/testing/selftests/ve/.gitignore
@@ -1,3 +1,4 @@
ve_ns_owner_test
ve_perms_test
ve_mount_accounting_test
+ve_vtty_stress
diff --git a/tools/testing/selftests/ve/Makefile b/tools/testing/selftests/ve/Makefile
index c6efe7c4b4fb..d287a73c5e97 100644
--- a/tools/testing/selftests/ve/Makefile
+++ b/tools/testing/selftests/ve/Makefile
@@ -1,9 +1,10 @@
# SPDX-License-Identifier: GPL-2.0
# Makefile for ve selftests.
-CFLAGS += -g -Wall -O2
+CFLAGS += -g -Wall -O2 $(KHDR_INCLUDES)
TEST_GEN_PROGS += ve_ns_owner_test
TEST_GEN_PROGS += ve_perms_test
TEST_GEN_PROGS += ve_mount_accounting_test
+TEST_GEN_PROGS += ve_vtty_stress
include ../lib.mk
diff --git a/tools/testing/selftests/ve/ve_vtty_stress.c b/tools/testing/selftests/ve/ve_vtty_stress.c
new file mode 100644
index 000000000000..8be6955d1dbc
--- /dev/null
+++ b/tools/testing/selftests/ve/ve_vtty_stress.c
@@ -0,0 +1,343 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * ve_vtty_stress - open and close a vtty pair from both ends at once.
+ *
+ * Either end of a vtty pair creates it, and the last close tears it down.
+ *
+ * Hammer both ends. The master comes from the vzctl ioctl, which does
+ * not look the VE up. The slave is reachable only from inside the VE, as
+ * TTY_MAJOR minor 1..MAX_NR_VTTY_CONSOLES, which vtty_driver() maps to
+ * vttys index minor - 1, so the test builds a VE with cgroup2, sets
+ * ve.veid to the cgroup it made, and runs the slave side there.
+ *
+ * A warning does not stop the host, so the run reads the kernel log too.
+ * One read() of /dev/kmsg is one record, so the test matches vtty driver
+ * splats, as well as generic kernel warning/oops/kasan reports.
+ *
+ * Usage: ve_vtty_stress [seconds] (default 30, or $VE_VTTY_SECS)
+ */
+#define _GNU_SOURCE
+#include <sched.h>
+#include <stdbool.h>
+#include <sys/ioctl.h>
+#include <sys/prctl.h>
+#include <sys/statvfs.h>
+#include <linux/major.h>
+#include <linux/vzcalluser.h>
+#include <sys/sysmacros.h>
+#include <sys/wait.h>
+#include <time.h>
+
+#include "ve_selftest.h"
+#include "../kselftest.h"
+
+#define VTTY_IDX 0 /* The pair both ends work on */
+#define SLAVE_MINOR (VTTY_IDX + 1) /* vtty_driver(): index = minor - 1 */
+#define DEFAULT_SECS 30
+
+/*
+ * Expected open errno codes: the pair may be closing, or gone already,
+ * when an open lands on it.
+ * Anything else is an environment issue or a bug.
+ */
+static bool expected_errno(int err)
+{
+ return err == EBUSY || err == EIO || err == ENXIO;
+}
+
+static int open_master(int ctl_fd, unsigned int veid)
+{
+ struct vzctl_ve_configure c = {
+ .veid = veid,
+ .key = VE_CONFIGURE_OPEN_TTY,
+ .val = VTTY_IDX,
+ };
+
+ return ioctl(ctl_fd, VZCTL_VE_CONFIGURE, &c);
+}
+
+/* Any key but the tty one makes ve_configure() look a running VE up */
+static bool veid_in_use(int ctl_fd, unsigned int veid)
+{
+ struct vzctl_ve_configure c = {
+ .veid = veid,
+ .key = VE_CONFIGURE_OS_RELEASE,
+ };
+
+ return ioctl(ctl_fd, VZCTL_VE_CONFIGURE, &c) < 0 && errno == ENOKEY;
+}
+
+/* The slave end, inside the VE. Returns the errno that stopped it, or 0. */
+static int hammer_slave(const char *node, time_t deadline,
+ unsigned long *opened)
+{
+ int err = 0;
+
+ while (time(NULL) < deadline) {
+ int fd = open(node, O_RDWR | O_NOCTTY | O_NONBLOCK);
+
+ if (fd >= 0) {
+ (*opened)++;
+ close(fd);
+ } else if (!expected_errno(errno)) {
+ err = errno;
+ break;
+ }
+ }
+
+ return err;
+}
+
+/* The kernel log, since a warning fails nothing by itself. */
+static int kmsg_open(void)
+{
+ int fd = open("/dev/kmsg", O_RDONLY | O_NONBLOCK);
+
+ if (fd >= 0)
+ lseek(fd, 0, SEEK_END);
+ return fd;
+}
+
+/*
+ * Check for kernel log warnings, one read() per record, hence
+ * the function name is not checked.
+ */
+static int kmsg_check(int fd)
+{
+ char buf[8192];
+ int found = 0;
+ ssize_t r;
+
+ if (fd < 0)
+ return 0;
+
+ for (;;) {
+ r = read(fd, buf, sizeof(buf) - 1);
+ if (r < 0) {
+ /* Ring overrun, continue with the oldest existing record */
+ if (errno == EPIPE)
+ continue;
+ break;
+ }
+ if (r == 0)
+ break;
+ buf[r] = '\0';
+ /* Known symptoms of a buggy kernel */
+ if (strstr(buf, "vtty") && (strstr(buf, "tty->count") ||
+ strstr(buf, "bad slave count"))) {
+ ksft_print_msg("vtty mismatched count log: %s", buf);
+ found++;
+ }
+ if (strstr(buf, "WARNING: ") || strstr(buf, "Oops: ") ||
+ strstr(buf, ";BUG: ") || strstr(buf, "soft lockup - ") ||
+ strstr(buf, "general protection fault")) {
+ ksft_print_msg("kernel log: %s", buf);
+ found++;
+ }
+ }
+ return found;
+}
+
+int main(int argc, char **argv)
+{
+ unsigned long master_opened = 0, slave_opened = 0;
+ int cg, ctid, ctl, kmsg, ready[2], count[2], status;
+ int master_err = 0, slave_err;
+ const char *env = getenv("VE_VTTY_SECS");
+ char path[PATH_MAX], val[16], c;
+ char dir[] = "/tmp/ve_vtty_XXXXXX";
+ char node[sizeof(dir) + 6];
+ struct namespace_ctx ns;
+ struct statvfs st;
+ time_t deadline;
+ long secs;
+ pid_t pid;
+
+ ksft_print_header();
+ secs = argc > 1 ? atol(argv[1]) : (env ? atol(env) : DEFAULT_SECS);
+ if (secs <= 0)
+ secs = DEFAULT_SECS;
+
+ ctl = open("/dev/vzctl", O_RDWR);
+ if (ctl < 0)
+ ksft_exit_skip("cannot open /dev/vzctl: %s, the vz modules "
+ "(vzdev, vzmon) are needed\n",
+ strerror(errno));
+
+ cg = mount_cg2_fd();
+ if (cg < 0)
+ ksft_exit_skip("cannot mount cgroup2: %s\n", strerror(errno));
+ if (write_file_at(cg, "cgroup.subtree_control", VE_CONTROLLERS) < 0)
+ ksft_exit_skip("cannot enable the ve controller: %s\n",
+ strerror(errno));
+
+ ctid = make_ve(cg, CTID_MIN);
+ if (ctid < 0)
+ ksft_exit_skip("cannot make a VE cgroup\n");
+
+ /* The vtty map is keyed by veid, and ve.veid takes a taken one */
+ if (veid_in_use(ctl, ctid)) {
+ destroy_ve(cg, ctid);
+ ksft_exit_skip("veid %d is in use by a running container\n",
+ ctid);
+ }
+
+ /* The ve.veid must match between master / slave */
+ snprintf(path, sizeof(path), "%d/ve.veid", ctid);
+ snprintf(val, sizeof(val), "%d", ctid);
+ if (write_file_at(cg, path, val) < 0) {
+ destroy_ve(cg, ctid);
+ ksft_exit_skip("cannot set ve.veid: %s\n", strerror(errno));
+ }
+
+ /* Do not report a failure where the vtty pair cannot be had at all */
+ status = open_master(ctl, ctid);
+ if (status < 0 && errno != EBUSY) {
+ destroy_ve(cg, ctid);
+ ksft_exit_skip("no vtty master: %s\n", strerror(errno));
+ }
+ if (status >= 0)
+ close(status);
+
+ /*
+ * Use temp directory for the node the slave end opens.
+ * Cleaned up by the master side instead of relying on the slave.
+ */
+ if (!mkdtemp(dir)) {
+ destroy_ve(cg, ctid);
+ ksft_exit_fail_msg("mkdtemp: %s\n", strerror(errno));
+ }
+ /* A nodev mount takes the mknod() and refuses every open */
+ if (statvfs(dir, &st) == 0 && (st.f_flag & ST_NODEV)) {
+ rmdir(dir);
+ destroy_ve(cg, ctid);
+ ksft_exit_skip("%s is on a nodev filesystem\n", dir);
+ }
+ snprintf(node, sizeof(node), "%s/slave", dir);
+ if (mknod(node, S_IFCHR | 0600, makedev(TTY_MAJOR, SLAVE_MINOR)) < 0) {
+ status = errno;
+ rmdir(dir);
+ destroy_ve(cg, ctid);
+ ksft_exit_fail_msg("mknod: %s\n", strerror(status));
+ }
+
+ ksft_set_plan(1);
+ kmsg = kmsg_open();
+ if (kmsg < 0)
+ ksft_print_msg("cannot read /dev/kmsg: %s, only a crash will "
+ "be noticed\n",
+ strerror(errno));
+
+ if (pipe(ready) || pipe(count)) {
+ unlink(node);
+ rmdir(dir);
+ destroy_ve(cg, ctid);
+ ksft_exit_fail_msg("pipe: %s\n", strerror(errno));
+ }
+
+ /* The VE of the cgroup, which the slave side enters */
+ if (prepare_namespaces(&ns, CLONE_NEWVE, cg, ctid) < 0) {
+ unlink(node);
+ rmdir(dir);
+ destroy_ve(cg, ctid);
+ ksft_exit_fail_msg("cannot prepare the VE namespace\n");
+ }
+
+ deadline = time(NULL) + secs;
+ ksft_print_msg("VE %d, pair %d, %ld seconds\n", ctid, VTTY_IDX, secs);
+
+ pid = fork();
+ if (pid == 0) {
+ unsigned long n = 0;
+ int err;
+
+ close(ready[0]);
+ close(count[0]);
+ /*
+ * Hammering on after the run has given up would hold
+ * the cgroup open against destroy_ve().
+ */
+ prctl(PR_SET_PDEATHSIG, SIGKILL);
+ if (enter_cgroup(cg, ctid) < 0 ||
+ enter_namespaces(&ns, CLONE_NEWVE) < 0)
+ _exit(errno);
+
+ c = 'r';
+ if (write(ready[1], &c, 1) != 1)
+ _exit(errno);
+ err = hammer_slave(node, deadline, &n);
+ /* Send the count either way: it says how far it got. */
+ if (write(count[1], &n, sizeof(n)) != sizeof(n))
+ _exit(errno);
+ _exit(err);
+ } else if (pid < 0) {
+ close_namespace_fds(&ns);
+ unlink(node);
+ rmdir(dir);
+ destroy_ve(cg, ctid);
+ ksft_exit_fail_msg("fork: %s\n", strerror(errno));
+ }
+ close(ready[1]);
+ close(count[1]);
+
+ if (read(ready[0], &c, 1) != 1) {
+ waitpid(pid, &status, 0);
+ close_namespace_fds(&ns);
+ unlink(node);
+ rmdir(dir);
+ destroy_ve(cg, ctid);
+ ksft_exit_fail_msg("the VE side never came up: %s\n",
+ strerror(WIFEXITED(status) ?
+ WEXITSTATUS(status) : EINTR));
+ }
+
+ while (time(NULL) < deadline) {
+ int fd = open_master(ctl, ctid);
+
+ if (fd >= 0) {
+ master_opened++;
+ close(fd);
+ } else if (!expected_errno(errno)) {
+ master_err = errno;
+ break;
+ }
+ }
+
+ if (master_err) {
+ /* The other end runs to its own deadline, stop it */
+ kill(pid, SIGKILL);
+ waitpid(pid, &status, 0);
+ slave_err = 0;
+ } else {
+ if (read(count[0], &slave_opened, sizeof(slave_opened)) !=
+ sizeof(slave_opened))
+ slave_opened = 0;
+ waitpid(pid, &status, 0);
+ slave_err = WIFEXITED(status) ? WEXITSTATUS(status) : EINTR;
+ }
+
+ ksft_print_msg("%lu master opens, %lu slave opens\n", master_opened,
+ slave_opened);
+
+ status = kmsg_check(kmsg);
+ close_namespace_fds(&ns);
+ unlink(node);
+ rmdir(dir);
+ destroy_ve(cg, ctid);
+
+ if (master_err)
+ ksft_exit_fail_msg("the master end stopped: %s\n",
+ strerror(master_err));
+ if (slave_err)
+ ksft_exit_fail_msg("the slave end stopped: %s\n",
+ strerror(slave_err));
+ if (!master_opened)
+ ksft_exit_fail_msg("no master was ever opened\n");
+ if (!slave_opened)
+ ksft_exit_fail_msg("no slave was ever opened\n");
+ if (status)
+ ksft_exit_fail_msg("kernel complained %d time(s)\n", status);
+
+ ksft_test_result_pass("vtty pair closed from both ends\n");
+ ksft_finished();
+}
--
2.55.0
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