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Subject[PATCH] tty: hvc_console, fix crashes on parallel open/close
Date
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>
Reported-and-tested-by: Raghavendra <rananta@codeaurora.org>
---
drivers/tty/hvc/hvc_console.c | 23 ++++++++---------------
1 file changed, 8 insertions(+), 15 deletions(-)

diff --git a/drivers/tty/hvc/hvc_console.c b/drivers/tty/hvc/hvc_console.c
index 436cc51c92c3..cdcc64ea2554 100644
--- 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 *tty, struct file * filp)
* 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 *tty, struct file * filp)

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 *tty, struct file * filp)
/* 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 *tty, struct file * filp)
* 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",
--
2.26.2
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