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Commit 229e1646 authored by Raghavendra Rao Ananta's avatar Raghavendra Rao Ananta Committed by Greg Kroah-Hartman
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tty: hvc: Fix data abort due to race in hvc_open 



[ Upstream commit e2bd1dcbe1aa34ff5570b3427c530e4332ecf0fe ]

Potentially, hvc_open() can be called in parallel when two tasks calls
open() on /dev/hvcX. In such a scenario, if the hp->ops->notifier_add()
callback in the function fails, where it sets the tty->driver_data to
NULL, the parallel hvc_open() can see this NULL and cause a memory abort.
Hence, serialize hvc_open and check if tty->private_data is NULL before
proceeding ahead.

The issue can be easily reproduced by launching two tasks simultaneously
that does nothing but open() and close() on /dev/hvcX.
For example:
$ ./simple_open_close /dev/hvc0 & ./simple_open_close /dev/hvc0 &

Signed-off-by: default avatarRaghavendra Rao Ananta <rananta@codeaurora.org>
Link: https://lore.kernel.org/r/20200428032601.22127-1-rananta@codeaurora.org


Signed-off-by: default avatarGreg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: default avatarSasha Levin <sashal@kernel.org>
parent f7199b98

drivers/tty/hvc/hvc_console.c

+14 −2
Original line number Diff line number Diff line
@@ -75,6 +75,8 @@ static LIST_HEAD(hvc_structs); 
 */

static DEFINE_MUTEX(hvc_structs_mutex);



/* Mutex to serialize hvc_open */

static DEFINE_MUTEX(hvc_open_mutex);

/*

 * This value is used to assign a tty->index value to a hvc_struct based

 * upon order of exposure via hvc_probe(), when we can not match it to
@@ -346,16 +348,24 @@ static int hvc_install(struct tty_driver *driver, struct tty_struct *tty) 
 */

static int hvc_open(struct tty_struct *tty, struct file * filp)

{

	struct hvc_struct *hp = tty->driver_data;

	struct hvc_struct *hp;

	unsigned long flags;

	int rc = 0;



	mutex_lock(&hvc_open_mutex);



	hp = tty->driver_data;

	if (!hp) {

		rc = -EIO;

		goto out;

	}



	spin_lock_irqsave(&hp->port.lock, flags);

	/* Check and then increment for fast path open. */

	if (hp->port.count++ > 0) {

		spin_unlock_irqrestore(&hp->port.lock, flags);

		hvc_kick();

		return 0;

		goto out;

	} /* else count == 0 */

	spin_unlock_irqrestore(&hp->port.lock, flags);
@@ -383,6 +393,8 @@ static int hvc_open(struct tty_struct *tty, struct file * filp) 
	/* Force wakeup of the polling thread */

	hvc_kick();



out:

	mutex_unlock(&hvc_open_mutex);

	return rc;

}