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* Re: [PATCH] tty: hvc: Fix data abort due to race in hvc_open
@ 2020-04-28 12:48 Markus Elfring
  0 siblings, 0 replies; 18+ messages in thread
From: Markus Elfring @ 2020-04-28 12:48 UTC (permalink / raw)
  To: Raghavendra Rao Ananta, linuxppc-dev
  Cc: Greg Kroah-Hartman, Andrew Melnychenko, linux-kernel, Jiri Slaby

> Hence, serialize hvc_open and check if tty->private_data is NULL before
> proceeding ahead.

How do you think about to add the tag “Fixes” because of adjustments
for the data synchronisation?


…
> +++ b/drivers/tty/hvc/hvc_console.c
…
@@ -384,6 +394,8 @@ static int hvc_open(struct tty_struct *tty, struct file * filp)
…
> +out:
> +	mutex_unlock(&hvc_open_mutex);
>  	return rc;
>  }

I suggest to use the label “unlock” instead.

Regards,
Markus

^ permalink raw reply	[flat|nested] 18+ messages in thread
* [PATCH] tty: hvc: Fix data abort due to race in hvc_open
@ 2020-04-28  3:26 Raghavendra Rao Ananta
  2020-05-06  9:48 ` Greg KH
  0 siblings, 1 reply; 18+ messages in thread
From: Raghavendra Rao Ananta @ 2020-04-28  3:26 UTC (permalink / raw)
  To: gregkh, jslaby, andrew; +Cc: rananta, linuxppc-dev, linux-kernel

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@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);
 
@@ -384,6 +394,8 @@ 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;
 }
 
-- 
The Qualcomm Innovation Center, Inc. is a member of the Code Aurora Forum,
a Linux Foundation Collaborative Project

^ permalink raw reply	[flat|nested] 18+ messages in thread

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Thread overview: 18+ messages (download: mbox.gz / follow: Atom feed)
-- links below jump to the message on this page --
2020-04-28 12:48 [PATCH] tty: hvc: Fix data abort due to race in hvc_open Markus Elfring
  -- strict thread matches above, loose matches on Subject: below --
2020-04-28  3:26 Raghavendra Rao Ananta
2020-05-06  9:48 ` Greg KH
2020-05-10  1:30   ` rananta
2020-05-10  6:48     ` Greg KH
2020-05-11  7:23       ` rananta
2020-05-11  7:34         ` rananta
2020-05-11  7:41           ` Greg KH
2020-05-11  7:39         ` Greg KH
2020-05-12  7:22           ` Jiri Slaby
2020-05-12  8:25             ` Greg KH
2020-05-12 21:39               ` rananta
2020-05-13  7:04                 ` Greg KH
2020-05-14 23:22                   ` rananta
2020-05-15  7:30                     ` Greg KH
2020-05-15 19:21                       ` rananta
2020-05-20  9:38                     ` Jiri Slaby
2020-05-20 13:49                       ` rananta

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