CVE-2026-63892

In the Linux kernel, the following vulnerability has been resolved:

thunderbolt: property: Reject dirlen < 4 to prevent sizet underflow

On the non-root path, _tbpropertyparsedir() takes dirlen from entry->length (u16 widened to sizet). Two distinct OOB conditions follow when entry->length < 4:

1. The non-root path begins with kmemdup(&block[diroffset], sizeof(*dir->uuid), ...) which always reads 4 dwords from diroffset. tbpropertyentryvalid() only enforces diroffset + entry->length <= blocklen, so a crafted entry with diroffset close to the end of the property block and entry->length in 0..3 passes that gate but lets the UUID copy run off the block (e.g. diroffset = 497, dirlen = 3 in a 500-dword block reads block[497..501]).

2. After the kmemdup, contentlen = dirlen - 4 underflows sizet to ~SIZEMAX, 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.

Reject dir_len < 4 on the non-root path before the UUID kmemdup, which closes both holes.

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