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

From: Greg Kroah-Hartman
Date: Fri Apr 30 2021 - 10:21:32 EST

From: Oliver Neukum <oneukum@xxxxxxxx>

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@xxxxxxxx>
Cc: stable <stable@xxxxxxxxxxxxxxx>
Link: https://lore.kernel.org/r/20210421074513.4327-1-oneukum@xxxxxxxx
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
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);

if (--acm->susp_count)
goto out;

+ acm_unpoison_urbs(acm);
if (tty_port_initialized(&acm->port)) {
rv = usb_submit_urb(acm->ctrlurb, GFP_ATOMIC);