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UPSTREAM: tty: fix data race between tty_init_dev and flush of buf

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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.

Reviewed-by: Alan Cox <alan@linux.intel.com>
Cc: stable <stable@vger.kernel.org>

Change-Id: I3ba3cbd7dcb867a110878c8d0c47e6b920edd0b9
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Gaurav Kohli <gkohli@codeaurora.org>
(cherry-picked from commit b027e2298b)
This commit is contained in:
Gaurav Kohli 2018-01-23 13:16:34 +05:30 committed by Huibin Hong
parent cdd5397503
commit 020a3b1024
3 changed files with 11 additions and 3 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

8
drivers/tty/tty_io.c
View File

@ -1546,6 +1546,9 @@ struct tty_struct *tty_init_dev(struct tty_driver *driver, int idx)
"%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;
/*
@ -1556,6 +1559,7 @@ struct tty_struct *tty_init_dev(struct tty_driver *driver, int idx)
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;
@ -1569,9 +1573,11 @@ struct tty_struct *tty_init_dev(struct tty_driver *driver, int idx)
/* call the tty release_tty routine to clean out this slot */
err_release_tty:
tty_unlock(tty);
tty_ldisc_unlock(tty);
printk_ratelimited(KERN_INFO "tty_init_dev: ldisc open failed, "
"clearing slot %d\n", idx);
err_release_lock:
tty_unlock(tty);
release_tty(tty, idx);
return ERR_PTR(retval);
}

4
drivers/tty/tty_ldisc.c
View File

@ -321,7 +321,7 @@ static inline void __tty_ldisc_unlock(struct tty_struct *tty)
ldsem_up_write(&tty->ldisc_sem);
}
static int __lockfunc
int __lockfunc
tty_ldisc_lock(struct tty_struct *tty, unsigned long timeout)
{
int ret;
@ -333,7 +333,7 @@ tty_ldisc_lock(struct tty_struct *tty, unsigned long timeout)
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);

2
include/linux/tty.h
View File

@ -374,6 +374,8 @@ extern struct tty_struct *get_current_tty(void);
/* 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)
{ }