linux-kernel - [PATCH] tty: hvc: Fix data abort due to race in hvc

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [thread-next>] [day] [month] [year] [list]

Message-Id: <20200428032601.22127-1-rananta@codeaurora.org>
Date:   Mon, 27 Apr 2020 20:26:01 -0700
From:   Raghavendra Rao Ananta <rananta@...eaurora.org>
To:     gregkh@...uxfoundation.org, jslaby@...e.com, andrew@...nix.com
Cc:     rananta@...eaurora.org, linuxppc-dev@...ts.ozlabs.org,
        linux-kernel@...r.kernel.org
Subject: [PATCH] tty: hvc: Fix data abort due to race in hvc_open

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@...eaurora.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