CVE-2026-93095: hfsplus: validate thread record before delete key rebuild

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

hfsplus: validate thread record before delete key rebuild

hfsplusdeletecat() is called with str == NULL when the last open reference to an unlinked HFS+ hardlink backing inode is closed. In that case, the function finds the catalog thread by CNID and rebuilds the catalog key from thread.nodeName.

That reconstruction path reads thread.nodeName.length directly from the catalog B-tree into fd.searchkey and then copies length 2 bytes into fd.searchkey->cat.name.unicode. It does not first check that the found record is a thread record or that its size matches the thread name.

A corrupted image can therefore provide an oversized thread name length and make hfsbnoderead() write past the catalog search-key allocation.

Read the CNID record through hfsplusbrecreadcat(), which bounds the record read to sizeof(hfspluscatentry) and verifies that a thread record's size exactly matches nodeName.length. Together, these checks ensure an accepted thread name fits HFSPLUSMAXSTRLEN. Reject non-thread records before building the delete key from the validated thread name.

Share the thread-record-type helper between hfsplusfindcat() and hfsplusdeletecat().