On Mon, Apr 27, 2020 at 08:26:01PM -0700, Raghavendra Rao Ananta wrote: > 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 <rana...@codeaurora.org> > --- > 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 436cc51c92c3..ebe26fe5ac09 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);
Wait, why isn't this driver just calling tty_port_open() instead of trying to open-code all of this? Keeping a single mutext for open will not protect it from close, it will just slow things down a bit. There should already be a tty lock held by the tty core for open() to keep it from racing things, right? Try just removing all of this logic and replacing it with a call to tty_port_open() and see if that fixes this issue. As "proof" of this, I don't see other serial drivers needing a single mutex for their open calls, do you? thanks, greg k-h