Skip to contentSkip to conversation

USB: cdc-acm: fix minor-number release

PATCH Superseded Johan Hovold 2 participants 3 messages Sep 6, 2021 – Sep 7, 2021

Subsystems (3)
Stable branch USB USB ACM driver

v1 of 2 Superseded Latest is v2 →

lore
Share & tools
lore

Johan Hovold

author
#0 lore raw

PATCH 1/1 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]>
---
 drivers/usb/class/cdc-acm.c | 7 +++++--
 1 file changed, 5 insertions(+), 2 deletions(-)
drivers/usb/class/cdc-acm.c +5 -2
index 4895325b16a4..5f0260bc4469 100644
@@ -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;
Signature · 1 line
2.32.0
maintainer
#1 lore raw

drivers/usb/class/cdc-acm.c static int acm_probe(struct usb_interface *intf, · line 1329

Quoted 8 lines · Johan Hovold
drivers/usb/class/cdc-acm.c +2 -1
@@ -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;

Hi,

Congratulations for catching that one.

May I request to improve understandability of the code that you give the constant a distinct name for this purpose? Something like

ACM_MINOR_POISON or ACM_INVALID_MINOR

so that normal people can understand the fixed code?

    Regards
        Oliver

author
#2 lore raw
Quoted 5 lines · Oliver Neukum
Quoted 3 lines · Johan Hovold
drivers/usb/class/cdc-acm.c +0 -0
@@ -1323,8 +1324,10 @@ static int acm_probe(struct usb_interface *intf,
 	usb_get_intf(acm->control); /* undone in destruct() */
Quoted 7 lines

drivers/usb/class/cdc-acm.c static int acm_probe(struct usb_interface *intf, · line 1329

Quoted 5 lines
drivers/usb/class/cdc-acm.c +2 -1
 	minor = acm_alloc_minor(acm);
-	if (minor < 0)
+	if (minor < 0) {
+		acm->minor = ACM_TTY_MINORS;
 		goto err_put_port;

Congratulations for catching that one.

Heh, thanks.

Quoted 6 lines

May I request to improve understandability of the code that you give the constant a distinct name for this purpose? Something like

ACM_MINOR_POISON or ACM_INVALID_MINOR

so that normal people can understand the fixed code?

Sure, I'll use ACM_MINOR_INVALID.

Johan