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// SPDX-License-Identifier: GPL-2.0-or-later
* Copyright (c) 2020 SUSE
* [Description]
* Test based on Syzkaller reproducer:
* The SLIP and SLCAN disciplines can have a race between write_wakeup and
* close/hangup. This at least allows the netdev private data (tty->disc_data)
* to be set to NULL or possibly freed while a transmit operation is being
* added to a workqueue.
* If the race condition exists, then the most likely result of running this
* is a null pointer dereference.
* Note that we must set the line discipline to "mouse" first which, for
* whatever reason, results in tty_wakeup being called during the close
* operation.
* We also test a selection of other line disciplines, but only SLIP and SLCAN
* are known to have the problem.
* Fixed by commit from v5.5:
* 0ace17d56824 ("can, slip: Protect tty->disc_data in write_wakeup and close with RCU")
* This is also regression test for commit from v4.5-rc1:
* dd42bf119714 ("tty: Prevent ldisc drivers from re-using stale tty fields")
#define _GNU_SOURCE
#include <stdlib.h>
#include <stdio.h>
#include <errno.h>
#include <termios.h>
#include "lapi/ioctl.h"
#include "tst_test.h"
#include "tst_safe_stdio.h"
#include "tst_fuzzy_sync.h"
struct ldisc_info {
int n;
char *name;
static struct ldisc_info ldiscs[] = {
{2, "mouse"},
{1, "SLIP"},
{3, "Async PPP"},
{5, "AX25/KISS"},
{13, "HDLC"},
{14, "Sync PPP"},
{17, "SLCAN"},
{18, "PPS"},
{20, "CAIF"},
{21, "GSM"}
static struct tst_fzsync_pair fzp;
static volatile int ptmx;
static void *hangup(void *unused)
int i;
while (tst_fzsync_run_b(&fzp)) {
for (i = 0; i < 10; i++) {
if (tcflush(ptmx, TCIFLUSH))
tst_brk(TBROK | TERRNO, "tcflush(ptmx, TCIFLUSH)");
return unused;
static int set_ldisc(int tty, struct ldisc_info *ldisc)
TEST(ioctl(tty, TIOCSETD, &ldisc->n));
if (!TST_RET)
return 0;
if (TST_ERR == EINVAL) {
tst_res(TCONF | TTERRNO,
"You don't appear to have the %s TTY line discipline",
} else {
tst_res(TFAIL | TTERRNO,
"Failed to set the %s line discipline", ldisc->name);
return 1;
static void do_test(unsigned int n)
int pts;
char pts_path[PATH_MAX];
struct ldisc_info *ldisc = &ldiscs[n + 1];
tst_res(TINFO, "Creating PTY with %s line discipline", ldisc->name);
tst_fzsync_pair_reset(&fzp, hangup);
while (tst_fzsync_run_a(&fzp)) {
ptmx = SAFE_OPEN("/dev/ptmx", O_RDONLY);
if (grantpt(ptmx))
tst_brk(TBROK | TERRNO, "grantpt(ptmx)");
if (unlockpt(ptmx))
tst_brk(TBROK | TERRNO, "unlockpt(ptmx)");
if (ptsname_r(ptmx, pts_path, sizeof(pts_path)))
tst_brk(TBROK | TERRNO, "ptsname_r(ptmx, ...)");
pts = SAFE_OPEN(pts_path, O_RDONLY);
if (set_ldisc(pts, &ldiscs[0]))
tst_brk(TCONF, "Need to set mouse discipline first");
if (set_ldisc(pts, ldisc))
ioctl(pts, TIOCVHANGUP);
tst_res(TPASS, "Did not crash with %s TTY discipline", ldisc->name);
static void setup(void)
fzp.min_samples = 20;
static void cleanup(void)
static struct tst_test test = {
.test = do_test,
.tcnt = 9,
.setup = setup,
.cleanup = cleanup,
.needs_root = 1,
.max_runtime = 30,
.needs_kconfigs = (const char *const[]){
.tags = (const struct tst_tag[]) {
{"linux-git", "0ace17d568241"},
{"CVE", "2020-14416"},
{"linux-git", "dd42bf1197144"},