netdev - [PATCHv2 2/4] USB: wdm: close race between wdm_open and wdm_wwan_port

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Message-ID: <20250401084749.175246-3-oneukum@suse.com>
Date: Tue,  1 Apr 2025 10:45:39 +0200
From: Oliver Neukum <oneukum@...e.com>
To: gregkh@...uxfoundation.org,
	bjorn@...k.no,
	loic.poulain@...aro.org,
	linux-usb@...r.kernel.org,
	netdev@...r.kernel.org
Cc: Oliver Neukum <oneukum@...e.com>
Subject: [PATCHv2 2/4] USB: wdm: close race between wdm_open and wdm_wwan_port_stop

Clearing WDM_WWAN_IN_USE must be the last action or
we can open a chardev whose URBs are still poisoned

V2: added memory barriers

Fixes: cac6fb015f71 ("usb: class: cdc-wdm: WWAN framework integration")
Signed-off-by: Oliver Neukum <oneukum@...e.com>
---
 drivers/usb/class/cdc-wdm.c | 6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

diff --git a/drivers/usb/class/cdc-wdm.c b/drivers/usb/class/cdc-wdm.c
index 12038aa43942..355627982343 100644
--- a/drivers/usb/class/cdc-wdm.c
+++ b/drivers/usb/class/cdc-wdm.c
@@ -728,7 +728,7 @@ static int wdm_open(struct inode *inode, struct file *file)
 		rv = -EBUSY;
 		goto out;
 	}
-
+	smp_rmb(); /* ordered against wdm_wwan_port_stop() */
 	rv = usb_autopm_get_interface(desc->intf);
 	if (rv < 0) {
 		dev_err(&desc->intf->dev, "Error autopm - %d\n", rv);
@@ -870,8 +870,10 @@ static void wdm_wwan_port_stop(struct wwan_port *port)
 	poison_urbs(desc);
 	desc->manage_power(desc->intf, 0);
 	clear_bit(WDM_READ, &desc->flags);
-	clear_bit(WDM_WWAN_IN_USE, &desc->flags);
 	unpoison_urbs(desc);
+	smp_wmb(); /* ordered against wdm_open() */
+	/* this must be last lest we open a poisoned device */
+	clear_bit(WDM_WWAN_IN_USE, &desc->flags);
 }
 
 static void wdm_wwan_port_tx_complete(struct urb *urb)
-- 
2.49.0