This is a note to let you know that I've just added the patch titled
tty: fix data race between tty_init_dev and flush of buf
to the 4.14-stable tree which can be found at: http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git%3Ba=su...
The filename of the patch is: tty-fix-data-race-between-tty_init_dev-and-flush-of-buf.patch and it can be found in the queue-4.14 subdirectory.
If you, or anyone else, feels it should not be added to the stable tree, please let stable@vger.kernel.org know about it.
From b027e2298bd588d6fa36ed2eda97447fb3eac078 Mon Sep 17 00:00:00 2001
From: Gaurav Kohli gkohli@codeaurora.org Date: Tue, 23 Jan 2018 13:16:34 +0530 Subject: tty: fix data race between tty_init_dev and flush of buf
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 @@ -1322,6 +1322,9 @@ 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;
/* @@ -1332,6 +1335,7 @@ 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;
@@ -1344,9 +1348,11 @@ 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 @@ -405,6 +405,8 @@ extern const char *tty_name(const struct 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) { }
Patches currently in stable-queue which might be from gkohli@codeaurora.org are
queue-4.14/tty-fix-data-race-between-tty_init_dev-and-flush-of-buf.patch