CVE-2026-80923: xhci: dbgtty: Fix unregister on tty_register_driver() failure

CVE-2026-80923: xhci: dbgtty: Fix unregister on tty_register_driver() failure

[Greg Kroah-Hartman]

From: Greg Kroah-Hartman <gregkh@kernel.org>

Description
===========

In the Linux kernel, the following vulnerability has been resolved:

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

The Linux kernel CVE team has assigned CVE-2026-80923 to this issue.


Affected and fixed versions
===========================

	Issue introduced in 5.9 with commit 4521f16139409cdf9462c7325d43454462cff6c3 and fixed in 5.15.220 with commit 01b7bc0938061f2fd46e0094f6483d8c6c02f7d3
	Issue introduced in 5.9 with commit 4521f16139409cdf9462c7325d43454462cff6c3 and fixed in 6.1.187 with commit 43635ff6401ca0e0ed21875379eeded921321525
	Issue introduced in 5.9 with commit 4521f16139409cdf9462c7325d43454462cff6c3 and fixed in 6.6.156 with commit eaca2814f32b9872a332326324b9e83e01f156d2
	Issue introduced in 5.9 with commit 4521f16139409cdf9462c7325d43454462cff6c3 and fixed in 6.12.108 with commit 943f976c93e70563b132f5585ff68b08c89641a2
	Issue introduced in 5.9 with commit 4521f16139409cdf9462c7325d43454462cff6c3 and fixed in 6.18.49 with commit 0d0faf3cc44c4d86fc6faf5cea972c0fbe00b922
	Issue introduced in 5.9 with commit 4521f16139409cdf9462c7325d43454462cff6c3 and fixed in 7.1.13 with commit 33ed35ca629477f57e0dd1d77d6df96cf5a9eb55
	Issue introduced in 5.9 with commit 4521f16139409cdf9462c7325d43454462cff6c3 and fixed in 7.2.3 with commit 0e469b94fbba8eb03666da41dd1082b793c50c1a
	Issue introduced in 5.9 with commit 4521f16139409cdf9462c7325d43454462cff6c3 and fixed in 7.3-rc1 with commit a916fa66a43e10f63198b6ce978badffc678821a

Please see https://www.kernel.org for a full list of currently supported
kernel versions by the kernel community.

Unaffected versions might change over time as fixes are backported to
older supported kernel versions.  The official CVE entry at
	https://cve.org/CVERecord/?id=CVE-2026-80923
will be updated if fixes are backported, please check that for the most
up to date information about this issue.


Affected files
==============

The file(s) affected by this issue are:
	drivers/usb/host/xhci-dbgtty.c


Mitigation
==========

The Linux kernel CVE team recommends that you update to the latest
stable kernel version for this, and many other bugfixes.  Individual
changes are never tested alone, but rather are part of a larger kernel
release.  Cherry-picking individual commits is not recommended or
supported by the Linux kernel community at all.  If however, updating to
the latest release is impossible, the individual changes to resolve this
issue can be found at these commits:
	https://git.kernel.org/stable/c/01b7bc0938061f2fd46e0094f6483d8c6c02f7d3
	https://git.kernel.org/stable/c/43635ff6401ca0e0ed21875379eeded921321525
	https://git.kernel.org/stable/c/eaca2814f32b9872a332326324b9e83e01f156d2
	https://git.kernel.org/stable/c/943f976c93e70563b132f5585ff68b08c89641a2
	https://git.kernel.org/stable/c/0d0faf3cc44c4d86fc6faf5cea972c0fbe00b922
	https://git.kernel.org/stable/c/33ed35ca629477f57e0dd1d77d6df96cf5a9eb55
	https://git.kernel.org/stable/c/0e469b94fbba8eb03666da41dd1082b793c50c1a
	https://git.kernel.org/stable/c/a916fa66a43e10f63198b6ce978badffc678821a