lkml.org 
[lkml]   [2020]   [Apr]   [27]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
Patch in this message
/
From
Subject[PATCH] tty: hvc: Fix data abort due to race in hvc_open
Date
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
\
 
 \ /
  Last update: 2020-04-28 05:27    [W:0.085 / U:1.380 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site