CVE-2021-46904

In the Linux kernel, the following vulnerability has been resolved: net:
hso: fix null-ptr-deref during tty device unregistration Multiple ttys try
to claim the same the minor number causing a double unregistration of the
same device. The first unregistration succeeds but the next one results in
a null-ptr-deref. The get_free_serial_index() function returns an available
minor number but doesn’t assign it immediately. The assignment is done by
the caller later. But before this assignment, calls to
get_free_serial_index() would return the same minor number. Fix this by
modifying get_free_serial_index to assign the minor number immediately
after one is found to be and rename it to obtain_minor() to better reflect
what it does. Similary, rename set_serial_by_index() to release_minor() and
modify it to free up the minor number of the given hso_serial. Every
obtain_minor() should have corresponding release_minor() call.

Notes