From: Raghavendra Rao Ananta <rananta@xxxxxxxxxxxxxx> [ 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: Raghavendra Rao Ananta <rananta@xxxxxxxxxxxxxx> Link: https://lore.kernel.org/r/20200428032601.22127-1-rananta@xxxxxxxxxxxxxx Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx> Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx> --- drivers/tty/hvc/hvc_console.c | 16 ++++++++++++++-- 1 file changed, 14 insertions(+), 2 deletions(-) diff --git a/drivers/tty/hvc/hvc_console.c b/drivers/tty/hvc/hvc_console.c index cdcc64ea2554f..f8e43a6faea9b 100644 --- a/drivers/tty/hvc/hvc_console.c +++ b/drivers/tty/hvc/hvc_console.c @@ -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; } -- 2.25.1
