Medium [CVE-2026-63892] Reject dir_len < 4 to prevent size_t underflow

In the Linux kernel, the following vulnerability has been resolved: thunderbolt: property: Reject dir_len length (u16 widened to size_t).

Two distinct OOB conditions follow when entry->length uuid),...) which always reads 4 dwords from dir_offset. tb_property_entry_valid() only enforces dir_offset + entry->length length in 0..3 passes that gate but lets the UUID copy run off the block (e.g. dir_offset = 497, dir_len = 3 in a 500-dword block reads block[497..501]). 2.

After the kmemdup, content_len = dir_len - 4 underflows size_t to ~SIZE_MAX, nentries becomes SIZE_MAX / 4, and the entry walk runs OOB on each iteration until an entry fails validation or the kernel oopses on an unmapped page.

Also move INIT_LIST_HEAD(&dir->properties) up to immediately after the dir allocation so the new error-return path (and the existing uuid-alloc failure path) calling tb_property_free_dir() sees a walkable list rather than the zero-initialized NULL next/prev that list_for_each_entry_safe() would oops on.

When processing Thunderbolt properties on a non-root path, a crafted entry with a small entry->length value can lead to an out-of-bounds read. This occurs because the kmemdup function reads beyond the intended memory block and a size_t underflow causes further out-of-bounds memory access during entry processing.