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From: daelyong jeong <>
To: Greg KH <>,, LKML <>
Cc: Byoungyoung Lee <>,
	Kyungtae Kim <>,
Subject: [PATCH] tty: Fix data race in tty_insert_flip_string_fixed_flag()
Date: Fri, 20 Apr 2018 16:40:56 +0900	[thread overview]
Message-ID: <> (raw)

tty_insert_flip_string_fixed_flag() copies chars to the buffer indicated
by th->used and updates tb->used.
But it is possible that tty_insert_flip_string_fixed_flag() is executed
concurrently and tb->used is updated improperly.
It leads slab-out-of-bound write in tty_insert_flip_string_fixed_flag or
slab-out-of-bounds read in flush_to_ldisc.

BUG: KASAN: slab-out-of-bounds in
drivers/tty/tty_buffer.c:316 at addr ffff880114fcc121
Write of size 1792 by task syz-executor0/30017
CPU: 1 PID: 30017 Comm: syz-executor0 Not tainted 4.8.0 #1
Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS
rel-1.8.2-0-g33fbe13 by 04/01/2014
 0000000000000000 ffff88011638f888 ffffffff81694cc3 ffff88007d802140
 ffff880114fcb300 ffff880114fcc300 ffff880114fcb300 ffff88011638f8b0
 ffffffff8130075c ffff88011638f940 ffff88007d802140 ffff880194fcc121
Call Trace:
 [<ffffffff81694cc3>] __dump_stack lib/dump_stack.c:15 [inline]
 [<ffffffff81694cc3>] dump_stack+0xb3/0x110 lib/dump_stack.c:51
 [<ffffffff8130075c>] kasan_object_err+0x1c/0x70 mm/kasan/report.c:156
 [<ffffffff813009f7>] print_address_description mm/kasan/report.c:194 [inline]
 [<ffffffff813009f7>] kasan_report_error+0x1f7/0x4e0 mm/kasan/report.c:283
 [<ffffffff81301076>] kasan_report+0x36/0x40 mm/kasan/report.c:303
 [<ffffffff812ff9ce>] check_memory_region_inline mm/kasan/kasan.c:292 [inline]
 [<ffffffff812ff9ce>] check_memory_region+0x13e/0x1a0 mm/kasan/kasan.c:299
 [<ffffffff812ffea7>] memcpy+0x37/0x50 mm/kasan/kasan.c:335
 [<ffffffff817f19f5>] tty_insert_flip_string_fixed_flag+0xb5/0x130
 [<ffffffff817f4d6f>] tty_insert_flip_string
include/linux/tty_flip.h:35 [inline]
 [<ffffffff817f4d6f>] pty_write+0x7f/0xc0 drivers/tty/pty.c:115
 [<ffffffff817f83c4>] n_hdlc_send_frames+0x1d4/0x3b0 drivers/tty/n_hdlc.c:419
 [<ffffffff817f8613>] n_hdlc_tty_wakeup+0x73/0xa0 drivers/tty/n_hdlc.c:496
 [<ffffffff817dea32>] tty_wakeup+0x92/0xb0 drivers/tty/tty_io.c:601
 [<ffffffff817e06c6>] __start_tty.part.26+0x66/0x70 drivers/tty/tty_io.c:1018
 [<ffffffff817e5114>] __start_tty+0x34/0x40 drivers/tty/tty_io.c:1013
 [<ffffffff817efbb6>] n_tty_ioctl_helper+0x146/0x1e0
 [<ffffffff817f9443>] n_hdlc_tty_ioctl+0xb3/0x2b0 drivers/tty/n_hdlc.c:794
 [<ffffffff817e4415>] tty_ioctl+0xa85/0x16d0 drivers/tty/tty_io.c:2992
 [<ffffffff8133500e>] vfs_ioctl fs/ioctl.c:43 [inline]
 [<ffffffff8133500e>] do_vfs_ioctl+0x13e/0xba0 fs/ioctl.c:679
 [<ffffffff81335aff>] SYSC_ioctl fs/ioctl.c:694 [inline]
 [<ffffffff81335aff>] SyS_ioctl+0x8f/0xc0 fs/ioctl.c:685
 [<ffffffff8230de3c>] entry_SYSCALL_64_fastpath+0x1f/0xbd

Call sequences are as follows.
CPU0                                    CPU1
n_tty_ioctl_helper                      n_tty_ioctl_helper
__start_tty                             tty_send_xchar
tty_wakeup                              pty_write
n_hdlc_tty_wakeup                       tty_insert_flip_string
n_hdlc_send_frames                      tty_insert_flip_string_fixed_flag

Acquire tty->atomic_write_lock by calling tty_write_lock() before
__start_tty() since __start_tty() can sends frames.

Signed-off-by: Daelyong Jeong <>
- Since tty_wakeup() called by __start_tty() sends frames, call
  tty_write_lock() before __start_tty().
- Since tty_write_lock() might sleep, locate tty_write_lock() before
- Since wake_up_interruptible_poll() is called by both tty_write_unlock()
  and __start_tty(), Prevent calling wake_up_interruptible_poll() twice
  by adding the wakeup flag to tty_write_unlock()

 drivers/tty/tty_io.c    | 16 +++++++++-------
 drivers/tty/tty_ioctl.c |  5 +++++
 include/linux/tty.h     |  2 ++
 3 files changed, 16 insertions(+), 7 deletions(-)

diff --git a/drivers/tty/tty_io.c b/drivers/tty/tty_io.c
index 63114ea..41f83bd 100644
--- a/drivers/tty/tty_io.c
+++ b/drivers/tty/tty_io.c
@@ -873,13 +873,15 @@ static ssize_t tty_read(struct file *file, char
__user *buf, size_t count,
  return i;

-static void tty_write_unlock(struct tty_struct *tty)
+void tty_write_unlock(struct tty_struct *tty, int wakeup)
- wake_up_interruptible_poll(&tty->write_wait, EPOLLOUT);
+ if (wakeup) {
+ wake_up_interruptible_poll(&tty->write_wait, EPOLLOUT);
+ }

-static int tty_write_lock(struct tty_struct *tty, int ndelay)
+int tty_write_lock(struct tty_struct *tty, int ndelay)
  if (!mutex_trylock(&tty->atomic_write_lock)) {
  if (ndelay)
@@ -973,7 +975,7 @@ static inline ssize_t do_tty_write(
  ret = written;
- tty_write_unlock(tty);
+ tty_write_unlock(tty, 1);
  return ret;

@@ -997,7 +999,7 @@ void tty_write_message(struct tty_struct *tty, char *msg)
  if (tty->ops->write && tty->count > 0)
  tty->ops->write(tty, msg, strlen(msg));
- tty_write_unlock(tty);
+ tty_write_unlock(tty, 1);
@@ -1092,7 +1094,7 @@ int tty_send_xchar(struct tty_struct *tty, char ch)
  if (was_stopped)
- tty_write_unlock(tty);
+ tty_write_unlock(tty, 1);
  return 0;

@@ -2395,7 +2397,7 @@ static int send_break(struct tty_struct *tty,
unsigned int duration)
  retval = tty->ops->break_ctl(tty, 0);
- tty_write_unlock(tty);
+ tty_write_unlock(tty, 1);
  if (signal_pending(current))
  retval = -EINTR;
diff --git a/drivers/tty/tty_ioctl.c b/drivers/tty/tty_ioctl.c
index d9b561d..a54ab91 100644
--- a/drivers/tty/tty_ioctl.c
+++ b/drivers/tty/tty_ioctl.c
@@ -911,12 +911,17 @@ int n_tty_ioctl_helper(struct tty_struct *tty,
struct file *file,
  case TCOON:
+ if (tty_write_lock(tty, 0) < 0)
+ return -ERESTARTSYS;
  if (tty->flow_stopped) {
  tty->flow_stopped = 0;
+ tty_write_unlock(tty, 0);
  case TCIOFF:
  if (STOP_CHAR(tty) != __DISABLED_CHAR)
diff --git a/include/linux/tty.h b/include/linux/tty.h
index 47f8af2..5bdf928 100644
--- a/include/linux/tty.h
+++ b/include/linux/tty.h
@@ -458,6 +458,8 @@ static inline struct tty_struct
*tty_kref_get(struct tty_struct *tty)
  return tty;

+extern void tty_write_unlock(struct tty_struct *tty, int wakeup);
+extern int tty_write_lock(struct tty_struct *tty, int ndelay);
 extern const char *tty_driver_name(const struct tty_struct *tty);
 extern void tty_wait_until_sent(struct tty_struct *tty, long timeout);
 extern int __tty_check_change(struct tty_struct *tty, int sig);

             reply	other threads:[~2018-04-20  7:40 UTC|newest]

Thread overview: 2+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2018-04-20  7:40 daelyong jeong [this message]
2018-04-20  8:14 ` Greg KH

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