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.