From 2b022ab7542df60021ab57854b3faaaf42552eaf Mon Sep 17 00:00:00 2001 From: Sahara Date: Wed, 13 Dec 2017 09:10:48 +0400 Subject: pty: cancel pty slave port buf's work in tty_release In case that CONFIG_SLUB_DEBUG is on and pty is used, races between release_one_tty and flush_to_ldisc work threads may happen and lead to use-after-free condition on tty->link->port. Because SLUB_DEBUG is turned on, freed tty->link->port is filled with POISON_FREE value. So far without SLUB_DEBUG, port was filled with zero and flush_to_ldisc could return without a problem by checking if tty is NULL. CPU 0 CPU 1 ----- ----- release_tty pty_write cancel_work_sync(tty) to = tty->link tty_kref_put(tty->link) tty_schedule_flip(to->port) << workqueue >> ... release_one_tty ... pty_cleanup ... kfree(tty->link->port) << workqueue >> flush_to_ldisc tty = READ_ONCE(port->itty) tty is 0x6b6b6b6b6b6b6b6b !!PANIC!! access tty->ldisc Unable to handle kernel paging request at virtual address 6b6b6b6b6b6b6b93 pgd = ffffffc0eb1c3000 [6b6b6b6b6b6b6b93] *pgd=0000000000000000, *pud=0000000000000000 ------------[ cut here ]------------ Kernel BUG at ffffff800851154c [verbose debug info unavailable] Internal error: Oops - BUG: 96000004 [#1] PREEMPT SMP CPU: 3 PID: 265 Comm: kworker/u8:9 Tainted: G W 3.18.31-g0a58eeb #1 Hardware name: Qualcomm Technologies, Inc. MSM 8996pro v1.1 + PMI8996 Carbide (DT) Workqueue: events_unbound flush_to_ldisc task: ffffffc0ed610ec0 ti: ffffffc0ed624000 task.ti: ffffffc0ed624000 PC is at ldsem_down_read_trylock+0x0/0x4c LR is at tty_ldisc_ref+0x24/0x4c pc : [] lr : [] pstate: 80400145 sp : ffffffc0ed627cd0 x29: ffffffc0ed627cd0 x28: 0000000000000000 x27: ffffff8009e05000 x26: ffffffc0d382cfa0 x25: 0000000000000000 x24: ffffff800a012f08 x23: 0000000000000000 x22: ffffffc0703fbc88 x21: 6b6b6b6b6b6b6b6b x20: 6b6b6b6b6b6b6b93 x19: 0000000000000000 x18: 0000000000000001 x17: 00e80000f80d6f53 x16: 0000000000000001 x15: 0000007f7d826fff x14: 00000000000000a0 x13: 0000000000000000 x12: 0000000000000109 x11: 0000000000000000 x10: 0000000000000000 x9 : ffffffc0ed624000 x8 : ffffffc0ed611580 x7 : 0000000000000000 x6 : ffffff800a42e000 x5 : 00000000000003fc x4 : 0000000003bd1201 x3 : 0000000000000001 x2 : 0000000000000001 x1 : ffffff800851004c x0 : 6b6b6b6b6b6b6b93 Signed-off-by: Sahara Signed-off-by: Greg Kroah-Hartman --- drivers/tty/tty_io.c | 2 ++ 1 file changed, 2 insertions(+) (limited to 'drivers/tty/tty_io.c') diff --git a/drivers/tty/tty_io.c b/drivers/tty/tty_io.c index dc60aeea87d8..a6ca634411e1 100644 --- a/drivers/tty/tty_io.c +++ b/drivers/tty/tty_io.c @@ -1476,6 +1476,8 @@ static void release_tty(struct tty_struct *tty, int idx) if (tty->link) tty->link->port->itty = NULL; tty_buffer_cancel_work(tty->port); + if (tty->link) + tty_buffer_cancel_work(tty->link->port); tty_kref_put(tty->link); tty_kref_put(tty); -- cgit v1.2.1 From b027e2298bd588d6fa36ed2eda97447fb3eac078 Mon Sep 17 00:00:00 2001 From: Gaurav Kohli Date: Tue, 23 Jan 2018 13:16:34 +0530 Subject: tty: fix data race between tty_init_dev and flush of buf 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 Reviewed-by: Alan Cox Cc: stable Signed-off-by: Greg Kroah-Hartman --- drivers/tty/tty_io.c | 8 +++++++- 1 file changed, 7 insertions(+), 1 deletion(-) (limited to 'drivers/tty/tty_io.c') diff --git a/drivers/tty/tty_io.c b/drivers/tty/tty_io.c index a6ca634411e1..688bd25aa6b0 100644 --- a/drivers/tty/tty_io.c +++ b/drivers/tty/tty_io.c @@ -1323,6 +1323,9 @@ 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; /* @@ -1333,6 +1336,7 @@ 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; @@ -1345,9 +1349,11 @@ 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); } -- cgit v1.2.1