4.9-stable review patch. If anyone has any objections, please let me know.
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From: Gaurav Kohli gkohli@codeaurora.org
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@codeaurora.org Reviewed-by: Alan Cox alan@linux.intel.com Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org
--- 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) { }