[PATCH] USB: cdc-acm: fix minor-number release

Johan Hovold
2021-09-06T12:44:38Z

If the driver runs out of minor numbers it would release minor 0 and
allow another device to claim the minor while still in use.

Fortunately, registering the tty class device of the second device would
fail (with a stack dump) due to the sysfs name collision so no memory is
leaked.

Fixes: cae2bc768d17 ("usb: cdc-acm: Decrement tty port's refcount if probe() fail")
Cc: stable@vger.kernel.org # 4.19
Cc: Jaejoong Kim <climbbb.kim@gmail.com>
Signed-off-by: Johan Hovold <johan@kernel.org>
---
drivers/usb/class/cdc-acm.c | 7 +++++--
1 file changed, 5 insertions(+), 2 deletions(-)

diff --git a/drivers/usb/class/cdc-acm.c b/drivers/usb/class/cdc-acm.c
index 4895325b16a4..5f0260bc4469 100644
--- a/drivers/usb/class/cdc-acm.c
+++ b/drivers/usb/class/cdc-acm.c
@@ -726,7 +726,8 @@ static void acm_port_destruct(struct tty_port *port)
{
struct acm *acm = container_of(port, struct acm, port);

- acm_release_minor(acm);
+ if (acm->minor != ACM_TTY_MINORS)
+ acm_release_minor(acm);
usb_put_intf(acm->control);
kfree(acm->country_codes);
kfree(acm);
@@ -1323,8 +1324,10 @@ static int acm_probe(struct usb_interface *intf,
usb_get_intf(acm->control); /* undone in destruct() */

minor = acm_alloc_minor(acm);
- if (minor < 0)
+ if (minor < 0) {
+ acm->minor = ACM_TTY_MINORS;
goto err_put_port;
+ }

acm->minor = minor;
acm->dev = usb_dev;
--
2.32.0