4.9-stable review patch. If anyone has any objections, please let me know.
------------------
From: Gaurav Kohli <gkohli@xxxxxxxxxxxxxx>
commit b027e2298bd588d6fa36ed2eda97447fb3eac078 upstream.
There can be a race, if receive_buf call comes before
tty initialization completes in n_tty_open and tty->disc_data
may be NULL.
CPU0 CPU1
---- ----
000|n_tty_receive_buf_common() n_tty_open()
-001|n_tty_receive_buf2() tty_ldisc_open.isra.3()
-002|tty_ldisc_receive_buf(inline) tty_ldisc_setup()
Using ldisc semaphore lock in tty_init_dev till disc_data
initializes completely.
Signed-off-by: Gaurav Kohli <gkohli@xxxxxxxxxxxxxx>
Reviewed-by: Alan Cox <alan@xxxxxxxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
drivers/tty/tty_io.c | 8 +++++++-
drivers/tty/tty_ldisc.c | 4 ++--
include/linux/tty.h | 2 ++
3 files changed, 11 insertions(+), 3 deletions(-)
--- a/drivers/tty/tty_io.c
+++ b/drivers/tty/tty_io.c
@@ -1543,6 +1543,9 @@ struct tty_struct *tty_init_dev(struct t
"%s: %s driver does not set tty->port. This will crash the kernel later. Fix the driver!\n",
__func__, tty->driver->name);
+ retval = tty_ldisc_lock(tty, 5 * HZ);
+ if (retval)
+ goto err_release_lock;
tty->port->itty = tty;
/*
@@ -1553,6 +1556,7 @@ struct tty_struct *tty_init_dev(struct t
retval = tty_ldisc_setup(tty, tty->link);
if (retval)
goto err_release_tty;
+ tty_ldisc_unlock(tty);
/* Return the tty locked so that it cannot vanish under the caller */
return tty;
@@ -1565,9 +1569,11 @@ err_module_put:
/* call the tty release_tty routine to clean out this slot */
err_release_tty:
- tty_unlock(tty);
+ tty_ldisc_unlock(tty);
tty_info_ratelimited(tty, "ldisc open failed (%d), clearing slot %d\n",
retval, idx);
+err_release_lock:
+ tty_unlock(tty);
release_tty(tty, idx);
return ERR_PTR(retval);
}
--- a/drivers/tty/tty_ldisc.c
+++ b/drivers/tty/tty_ldisc.c
@@ -336,7 +336,7 @@ static inline void __tty_ldisc_unlock(st
ldsem_up_write(&tty->ldisc_sem);
}
-static int tty_ldisc_lock(struct tty_struct *tty, unsigned long timeout)
+int tty_ldisc_lock(struct tty_struct *tty, unsigned long timeout)
{
int ret;
@@ -347,7 +347,7 @@ static int tty_ldisc_lock(struct tty_str
return 0;
}
-static void tty_ldisc_unlock(struct tty_struct *tty)
+void tty_ldisc_unlock(struct tty_struct *tty)
{
clear_bit(TTY_LDISC_HALTED, &tty->flags);
__tty_ldisc_unlock(tty);
--- a/include/linux/tty.h
+++ b/include/linux/tty.h
@@ -394,6 +394,8 @@ extern struct tty_struct *get_current_tt
/* tty_io.c */
extern int __init tty_init(void);
extern const char *tty_name(const struct tty_struct *tty);
+extern int tty_ldisc_lock(struct tty_struct *tty, unsigned long timeout);
+extern void tty_ldisc_unlock(struct tty_struct *tty);
#else
static inline void console_init(void)
{ }