3.16.83-rc1 review patch. If anyone has any objections, please let me know.
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From: Richard Palethorpe rpalethorpe@suse.com
commit 0ace17d56824165c7f4c68785d6b58971db954dd upstream.
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: 661f7fda21b1 ("slip: Fix deadlock in write_wakeup") Fixes: a8e83b17536a ("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 Signed-off-by: Ben Hutchings ben@decadent.org.uk --- drivers/net/can/slcan.c | 12 ++++++++++-- drivers/net/slip/slip.c | 12 ++++++++++-- 2 files changed, 20 insertions(+), 4 deletions(-)
--- a/drivers/net/can/slcan.c +++ b/drivers/net/can/slcan.c @@ -346,9 +346,16 @@ static void slcan_transmit(struct work_s */ 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. */ @@ -640,10 +647,11 @@ static void slcan_close(struct tty_struc 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 */ --- a/drivers/net/slip/slip.c +++ b/drivers/net/slip/slip.c @@ -452,9 +452,16 @@ static void slip_transmit(struct work_st */ 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) @@ -885,10 +892,11 @@ static void slip_close(struct tty_struct 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 */