2021-09-07 08:27:38

by Johan Hovold

Subject: [PATCH v2] USB: cdc-acm: fix minor-number release

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: [email protected] # 4.19
Cc: Jaejoong Kim <[email protected]>
Signed-off-by: Johan Hovold <[email protected]>
---

Changes in v2
- add a dedicated define for the invalid minor number (Oliver)


drivers/usb/class/cdc-acm.c | 7 +++++--
drivers/usb/class/cdc-acm.h | 2 ++
2 files changed, 7 insertions(+), 2 deletions(-)

diff --git a/drivers/usb/class/cdc-acm.c b/drivers/usb/class/cdc-acm.c
index 4895325b16a4..5b90d0979c60 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_MINOR_INVALID)
+ 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_MINOR_INVALID;
goto err_put_port;
+ }

acm->minor = minor;
acm->dev = usb_dev;
diff --git a/drivers/usb/class/cdc-acm.h b/drivers/usb/class/cdc-acm.h
index 8aef5eb769a0..3aa7f0a3ad71 100644
--- a/drivers/usb/class/cdc-acm.h
+++ b/drivers/usb/class/cdc-acm.h
@@ -22,6 +22,8 @@
#define ACM_TTY_MAJOR 166
#define ACM_TTY_MINORS 256

+#define ACM_MINOR_INVALID ACM_TTY_MINORS
+
/*
* Requests.
*/
--
2.32.0

2021-09-07 09:51:49

by Oliver Neukum

Subject: Re: [PATCH v2] USB: cdc-acm: fix minor-number release

On 07.09.21 10:23, Johan Hovold wrote:
> 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: [email protected] # 4.19
> Cc: Jaejoong Kim <[email protected]>
> Signed-off-by: Johan Hovold <[email protected]>
Acked-by: Oliver Neukum <[email protected]>