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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.

Signed-off-by: Gaurav Kohli <gkohli@codeaurora.org>
Reviewed-by: Alan Cox <alan@linux.intel.com>
Cc: stable <stable@vger.kernel.org>

Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
This commit is contained in:
Gaurav Kohli 2018-01-23 13:16:34 +05:30 • committed by Greg Kroah-Hartman
parent 09df0b3464
commit b027e2298b
3 changed files with 11 additions and 3 deletions
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2
include/linux/tty.h
View file

@ -405,6 +405,8 @@ extern const char *tty_name(const struct tty_struct *tty);
extern struct tty_struct *tty_kopen(dev_t device);
extern void tty_kclose(struct tty_struct *tty);
extern int tty_dev_name_to_number(const char *name, dev_t *number);
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 tty_kref_put(struct tty_struct *tty)
{ }