thunderbolt: property: Cap recursion depth in __tb_property_parse_dir()

In the Linux kernel, the following vulnerability has been resolved: thunderbolt: property: Cap recursion depth in __tb_property_parse_dir() A DIRECTORY entry's value field is used as the dir_offset for a recursive call into __tb_property_parse_dir() with no depth counter. A crafted peer that chains DIRECTORY entries into a back-reference loop drives the parser until the kernel stack is exhausted and the guard page fires. Any untrusted XDomain peer (cable, dock, in-line inspector, adjacent host) that reaches the PROPERTIES_REQUEST control-plane exchange can trigger this without authentication. Thread a depth counter through tb_property_parse() and __tb_property_parse_dir(), and reject blocks that exceed TB_PROPERTY_MAX_DEPTH = 8. That is comfortably larger than any observed legitimate XDomain layout. Operators who do not need XDomain host-to-host discovery can disable the path entirely with thunderbolt.xdomain=0 on the kernel command line.