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: cae2bc7 ("usb: cdc-acm: Decrement tty port's refcount if probe() fail") Cc: [email protected] # 4.19 Cc: Jaejoong Kim <[email protected]> Acked-by: Oliver Neukum <[email protected]> Signed-off-by: Johan Hovold <[email protected]> Link: https://lore.kernel.org/r/[email protected] Signed-off-by: Greg Kroah-Hartman <[email protected]>
zandrey · Sep 14, 2021 · 91fac07 · 91fac07
1 parent 856e6e8
commit 91fac07
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Showing 2 changed files with 7 additions and 2 deletions.
diff --git 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
@@ -22,6 +22,8 @@
 #define ACM_TTY_MAJOR		166
 #define ACM_TTY_MINORS		256
 
+#define ACM_MINOR_INVALID	ACM_TTY_MINORS
+
 /*
  * Requests.
  */