net: hso: fix null-ptr-deref during tty device unregistration

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.

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Linux kernel 安全漏洞

Linux kernel是美国Linux基金会的开源操作系统Linux所使用的内核。 Linux kernel存在安全漏洞，该漏洞源于tty设备注销期间存在NULL指针取消引用问题。

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