linux-kernel - [REGRESSION 5.19] NULL dereference by ucsi

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Message-ID: <87r11cmbx0.wl-tiwai@suse.de>
Date:   Fri, 19 Aug 2022 18:32:43 +0200
From:   Takashi Iwai <tiwai@...e.de>
To:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Cc:     Linyu Yuan <quic_linyyuan@...cinc.com>, linux-usb@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: [REGRESSION 5.19] NULL dereference by ucsi_acpi driver

Hi,

we've got multiple reports about 5.19 kernel starting crashing after
some time, and this turned out to be triggered by ucsi_acpi driver.
The details are found in:
  https://bugzilla.suse.com/show_bug.cgi?id=1202386

The culprit seems to be the commit 87d0e2f41b8c
    usb: typec: ucsi: add a common function ucsi_unregister_connectors()

This commit looks as if it were a harmless cleanup, but this failed in
a subtle way.  Namely, in the error scenario, the driver gets an error
at ucsi_register_altmodes(), and goes to the error handling to release
the resources.  Through this refactoring, the release part was unified
to a funciton ucsi_unregister_connectors().  And there, it has a NULL
check of con->wq, and it bails out the loop if it's NULL. 
Meanwhile, ucsi_register_port() itself still calls destroy_workqueue()
and clear con->wq at its error path.  This ended up in the leftover
power supply device with the uninitialized / cleared device.

It was confirmed that the problem could be avoided by a simple
revert.

I guess another fix could be removing the part clearing con->wq, i.e.

--- a/drivers/usb/typec/ucsi/ucsi.c
+++ b/drivers/usb/typec/ucsi/ucsi.c
@@ -1192,11 +1192,6 @@ static int ucsi_register_port(struct ucsi *ucsi, int index)
 out_unlock:
 	mutex_unlock(&con->lock);

-	if (ret && con->wq) {
-		destroy_workqueue(con->wq);
-		con->wq = NULL;
-	}
-
 	return ret;
 }

... but it's totally untested and I'm not entirely sure whether it's
better.

thanks,

Takashi