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can, slip: Protect tty->disc_data in write_wakeup and close with RCU 

write_wakeup can happen in parallel with close/hangup where tty->disc_data
is set to NULL and the netdevice is freed thus also freeing
disc_data. write_wakeup accesses disc_data so we must prevent close from
freeing the netdev while write_wakeup has a non-NULL view of
tty->disc_data.

We also need to make sure that accesses to disc_data are atomic. Which can
all be done with RCU.

This problem was found by Syzkaller on SLCAN, but the same issue is
reproducible with the SLIP line discipline using an LTP test based on the
Syzkaller reproducer.

A fix which didn't use RCU was posted by Hillf Danton.

Fixes: 661f7fda21 ("slip: Fix deadlock in write_wakeup")
Fixes: a8e83b1753 ("slcan: Port write_wakeup deadlock fix from slip")
Reported-by: syzbot+017e491ae13c0068598a@syzkaller.appspotmail.com
Signed-off-by: Richard Palethorpe <rpalethorpe@suse.com>
Cc: Wolfgang Grandegger <wg@grandegger.com>
Cc: Marc Kleine-Budde <mkl@pengutronix.de>
Cc: "David S. Miller" <davem@davemloft.net>
Cc: Tyler Hall <tylerwhall@gmail.com>
Cc: linux-can@vger.kernel.org
Cc: netdev@vger.kernel.org
Cc: linux-kernel@vger.kernel.org
Cc: syzkaller@googlegroups.com
Signed-off-by: David S. Miller <davem@davemloft.net>
alistair/sunxi64-5.5-dsi
Richard Palethorpe 2020-01-21 14:42:58 +01:00 committed by David S. Miller
parent 58c8db929d
commit 0ace17d568
2 changed files with 20 additions and 4 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

12
drivers/net/can/slcan.c
View File

@ -344,9 +344,16 @@ static void slcan_transmit(struct work_struct *work)
*/
static void slcan_write_wakeup(struct tty_struct *tty)
{
struct slcan *sl = tty->disc_data;
struct slcan *sl;
rcu_read_lock();
sl = rcu_dereference(tty->disc_data);
if (!sl)
goto out;
schedule_work(&sl->tx_work);
out:
rcu_read_unlock();
}
/* Send a can_frame to a TTY queue. */
@ -644,10 +651,11 @@ static void slcan_close(struct tty_struct *tty)
return;
spin_lock_bh(&sl->lock);
tty->disc_data = NULL;
rcu_assign_pointer(tty->disc_data, NULL);
sl->tty = NULL;
spin_unlock_bh(&sl->lock);
synchronize_rcu();
flush_work(&sl->tx_work);
/* Flush network side */

12
drivers/net/slip/slip.c
View File

@ -452,9 +452,16 @@ static void slip_transmit(struct work_struct *work)
*/
static void slip_write_wakeup(struct tty_struct *tty)
{
struct slip *sl = tty->disc_data;
struct slip *sl;
rcu_read_lock();
sl = rcu_dereference(tty->disc_data);
if (!sl)
goto out;
schedule_work(&sl->tx_work);
out:
rcu_read_unlock();
}
static void sl_tx_timeout(struct net_device *dev)
@ -882,10 +889,11 @@ static void slip_close(struct tty_struct *tty)
return;
spin_lock_bh(&sl->lock);
tty->disc_data = NULL;
rcu_assign_pointer(tty->disc_data, NULL);
sl->tty = NULL;
spin_unlock_bh(&sl->lock);
synchronize_rcu();
flush_work(&sl->tx_work);
/* VSV = very important to remove timers */