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

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Date:   Tue,  7 Sep 2021 10:23:18 +0200
From:   Johan Hovold <johan@...nel.org>
To:     Oliver Neukum <oneukum@...e.com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Cc:     linux-usb@...r.kernel.org, linux-kernel@...r.kernel.org,
        Johan Hovold <johan@...nel.org>, stable@...r.kernel.org,
        Jaejoong Kim <climbbb.kim@...il.com>
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: stable@...r.kernel.org      # 4.19
Cc: Jaejoong Kim <climbbb.kim@...il.com>
Signed-off-by: Johan Hovold <johan@...nel.org>
---

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