can, slip: Protect tty->disc_data in write_wakeup and close with RCU (0ace17d5) · Commits · 戴 / test

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: ("slip: Fix deadlock in write_wakeup") Fixes: ("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>

drivers/net/can/slcan.c

+10 −2

Original line number	Diff line number	Diff line
		@@ -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 */

drivers/net/slip/slip.c

+10 −2

Original line number	Diff line number	Diff line
		@@ -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 */

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