From: Jiri Slaby jslaby@suse.cz
commit 24eb2377f977fe06d84fca558f891f95bc28a449 upstream.
hvc_open sets tty->driver_data to NULL when open fails at some point. Typically, the failure happens in hp->ops->notifier_add(). If there is a racing process which tries to open such mangled tty, which was not closed yet, the process will crash in hvc_open as tty->driver_data is NULL.
All this happens because close wants to know whether open failed or not. But ->open should not NULL this and other tty fields for ->close to be happy. ->open should call tty_port_set_initialized(true) and close should check by tty_port_initialized() instead. So do this properly in this driver.
So this patch removes these from ->open: * tty_port_tty_set(&hp->port, NULL). This happens on last close. * tty->driver_data = NULL. Dtto. * tty_port_put(&hp->port). This happens in shutdown and until now, this must have been causing a reference underflow, if I am not missing something.
Signed-off-by: Jiri Slaby jslaby@suse.cz Cc: stable stable@vger.kernel.org Reported-and-tested-by: Raghavendra rananta@codeaurora.org Link: https://lore.kernel.org/r/20200526145632.13879-1-jslaby@suse.cz Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org
--- drivers/tty/hvc/hvc_console.c | 23 ++++++++--------------- 1 file changed, 8 insertions(+), 15 deletions(-)
--- a/drivers/tty/hvc/hvc_console.c +++ b/drivers/tty/hvc/hvc_console.c @@ -371,15 +371,14 @@ static int hvc_open(struct tty_struct *t * tty fields and return the kref reference. */ if (rc) { - tty_port_tty_set(&hp->port, NULL); - tty->driver_data = NULL; - tty_port_put(&hp->port); printk(KERN_ERR "hvc_open: request_irq failed with rc %d.\n", rc); - } else + } else { /* We are ready... raise DTR/RTS */ if (C_BAUD(tty)) if (hp->ops->dtr_rts) hp->ops->dtr_rts(hp, 1); + tty_port_set_initialized(&hp->port, true); + }
/* Force wakeup of the polling thread */ hvc_kick(); @@ -389,22 +388,12 @@ static int hvc_open(struct tty_struct *t
static void hvc_close(struct tty_struct *tty, struct file * filp) { - struct hvc_struct *hp; + struct hvc_struct *hp = tty->driver_data; unsigned long flags;
if (tty_hung_up_p(filp)) return;
- /* - * No driver_data means that this close was issued after a failed - * hvc_open by the tty layer's release_dev() function and we can just - * exit cleanly because the kref reference wasn't made. - */ - if (!tty->driver_data) - return; - - hp = tty->driver_data; - spin_lock_irqsave(&hp->port.lock, flags);
if (--hp->port.count == 0) { @@ -412,6 +401,9 @@ static void hvc_close(struct tty_struct /* We are done with the tty pointer now. */ tty_port_tty_set(&hp->port, NULL);
+ if (!tty_port_initialized(&hp->port)) + return; + if (C_HUPCL(tty)) if (hp->ops->dtr_rts) hp->ops->dtr_rts(hp, 0); @@ -428,6 +420,7 @@ static void hvc_close(struct tty_struct * waking periodically to check chars_in_buffer(). */ tty_wait_until_sent(tty, HVC_CLOSE_WAIT); + tty_port_set_initialized(&hp->port, false); } else { if (hp->port.count < 0) printk(KERN_ERR "hvc_close %X: oops, count is %d\n",