linux-kernel - [PATCH 5.12 2/5] USB: CDC-ACM: fix poison/unpoison imbalance

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Date:   Fri, 30 Apr 2021 16:20:57 +0200
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org, Oliver Neukum <oneukum@...e.com>
Subject: [PATCH 5.12 2/5] USB: CDC-ACM: fix poison/unpoison imbalance

From: Oliver Neukum <oneukum@...e.com>

commit a8b3b519618f30a87a304c4e120267ce6f8dc68a upstream.

suspend() does its poisoning conditionally, resume() does it
unconditionally. On a device with combined interfaces this
will balance, on a device with two interfaces the counter will
go negative and resubmission will fail.

Both actions need to be done conditionally.

Fixes: 6069e3e927c8f ("USB: cdc-acm: untangle a circular dependency between callback and softint")
Signed-off-by: Oliver Neukum <oneukum@...e.com>
Cc: stable <stable@...r.kernel.org>
Link: https://lore.kernel.org/r/20210421074513.4327-1-oneukum@suse.com
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
---
 drivers/usb/class/cdc-acm.c |    3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

--- a/drivers/usb/class/cdc-acm.c
+++ b/drivers/usb/class/cdc-acm.c
@@ -1634,12 +1634,13 @@ static int acm_resume(struct usb_interfa
 	struct urb *urb;
 	int rv = 0;
 
-	acm_unpoison_urbs(acm);
 	spin_lock_irq(&acm->write_lock);
 
 	if (--acm->susp_count)
 		goto out;
 
+	acm_unpoison_urbs(acm);
+
 	if (tty_port_initialized(&acm->port)) {
 		rv = usb_submit_urb(acm->ctrlurb, GFP_ATOMIC);