linux-kernel - [PATCH] tty: synclink_gt: unwind actions in error path of net device open

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Message-Id: <D2A8DDC3-9D72-4CDD-92A0-2C27146C1BE0@microgate.com>
Date:   Tue, 15 Nov 2022 09:18:41 -0800
From:   Paul Fulghum <paulkf@...rogate.com>
To:     Zhengchao Shao <shaozhengchao@...wei.com>
Cc:     "linux-kernel@...r.kernel.org Mailing List" 
        <linux-kernel@...r.kernel.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Jiri Slaby <jirislaby@...nel.org>, akpm@...ux-foundation.org,
        weiyongjun1@...wei.com, yuehaibing@...wei.com
Subject: [PATCH] tty: synclink_gt: unwind actions in error path of net device
 open

Resent in plain text, sorry for the previous HTML.

Zhengchao Shao <shaozhengchao@...wei.com> identified by inspection bugs in the error path of hdlcdev_open() in synclink_gt.c

The function did not fully unwind actions in the error path. The use of try_module_get()/module_put() is unnecessary, potentially hazardous and is removed. The synclink_gt driver is already pinned any point the net device is registered, a requirement for calling this entry point.

The call hdlc_open() to init the generic HDLC layer is moved to after driver level init/checks and proper rollback of previous actions is added. This is a more sensible ordering as the most common error paths are at the driver level and the driver level rollbacks require less processing than hdlc_open()/hdlc_close().

This has been tested with supported hardware.

Signed-off-by:Paul Fulghum <paulkf@...rogate.com>

diff --git a/drivers/tty/synclink_gt.c b/drivers/tty/synclink_gt.c
index 25e9befdda3a..72b76cdde534 100644
--- a/drivers/tty/synclink_gt.c
+++ b/drivers/tty/synclink_gt.c
@@ -1433,16 +1433,8 @@ static int hdlcdev_open(struct net_device *dev)
 	int rc;
 	unsigned long flags;
 
-	if (!try_module_get(THIS_MODULE))
-		return -EBUSY;
-
 	DBGINFO(("%s hdlcdev_open\n", dev->name));
 
-	/* generic HDLC layer open processing */
-	rc = hdlc_open(dev);
-	if (rc)
-		return rc;
-
 	/* arbitrate between network and tty opens */
 	spin_lock_irqsave(&info->netlock, flags);
 	if (info->port.count != 0 || info->netcount != 0) {
@@ -1461,6 +1453,16 @@ static int hdlcdev_open(struct net_device *dev)
 		return rc;
 	}
 
+	/* generic HDLC layer open processing */
+	rc = hdlc_open(dev);
+	if (rc) {
+		shutdown(info);
+		spin_lock_irqsave(&info->netlock, flags);
+		info->netcount = 0;
+		spin_unlock_irqrestore(&info->netlock, flags);
+		return rc;
+	}
+
 	/* assert RTS and DTR, apply hardware settings */
 	info->signals |= SerialSignal_RTS | SerialSignal_DTR;
 	program_hw(info);
@@ -1506,7 +1508,6 @@ static int hdlcdev_close(struct net_device *dev)
 	info->netcount=0;
 	spin_unlock_irqrestore(&info->netlock, flags);
 
-	module_put(THIS_MODULE);
 	return 0;
 }