FAILED: patch "[PATCH] xhci: dbgtty: Fix unregister on tty_register_driver() failure" failed to apply to 5.10-stable tree

[<gregkh@linuxfoundation.org>]

The patch below does not apply to the 5.10-stable tree.
If someone wants it applied there, or to any other stable or longterm
tree, then please email the backport, including the original git commit
id to <stable@vger.kernel.org>.

To reproduce the conflict and resubmit, you may use the following commands:

git fetch https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/ linux-5.10.y
git checkout FETCH_HEAD
git cherry-pick -x a916fa66a43e10f63198b6ce978badffc678821a
# <resolve conflicts, build, test, etc.>
git commit -s
git send-email --to '<stable@vger.kernel.org>' --in-reply-to '2026083142-everyday-fifteen-2ae3@gregkh' --subject-prefix 'PATCH 5.10.y' 'HEAD^..'

Possible dependencies:



thanks,

greg k-h

------------------ original commit in Linus's tree ------------------

From a916fa66a43e10f63198b6ce978badffc678821a Mon Sep 17 00:00:00 2001
From: Lucas De Marchi <ldemarchi@nvidia.com>
Date: Thu, 6 Aug 2026 17:21:03 +0300
Subject: [PATCH] xhci: dbgtty: Fix unregister on tty_register_driver() failure

If tty_register_driver() fails, it drops the reference, but fails to set
the global dbc_tty_driver to NULL, causing the unregister to be called
again when module exits.

On module unload dbc_tty_exit() only gates its cleanup on the driver
pointer being non-NULL, so it operates on the already-freed driver:

    module_init(xhci_hcd_init)
      xhci_hcd_init()
        xhci_dbc_init()                       [return value ignored]
          dbc_tty_init()
            tty_register_driver() fails
              tty_driver_kref_put()           -> driver freed
              (dbc_tty_driver left dangling)
    ...
    module_exit(xhci_hcd_fini)
      xhci_hcd_fini()
        xhci_dbc_exit()
          dbc_tty_exit()
            if (dbc_tty_driver)               -> true (dangling)
              tty_unregister_driver()         -> use-after-free

Fixes: 4521f1613940 ("xhci: dbctty: split dbc tty driver registration and unregistration functions.")
Cc: stable@vger.kernel.org # v5.10
Cc: Mathias Nyman <mathias.nyman@linux.intel.com>
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Lucas De Marchi <ldemarchi@nvidia.com>
Signed-off-by: Mathias Nyman <mathias.nyman@linux.intel.com>
Link: https://patch.msgid.link/20260806142113.2436238-8-mathias.nyman@linux.intel.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/drivers/usb/host/xhci-dbgtty.c b/drivers/usb/host/xhci-dbgtty.c
index 2e7384c6b6ec..01decd46f313 100644
--- a/drivers/usb/host/xhci-dbgtty.c
+++ b/drivers/usb/host/xhci-dbgtty.c
@@ -651,6 +651,7 @@ int dbc_tty_init(void)
 		pr_err("Can't register dbc tty driver\n");
 		tty_driver_kref_put(dbc_tty_driver);
 		idr_destroy(&dbc_tty_minors);
+		dbc_tty_driver = NULL;
 	}
 
 	return ret;