Merge branch 'fix-for-untrusted-btf-pointer-writes'

Kumar Kartikeya Dwivedi says:

====================
Fix for untrusted BTF pointer writes

When using custom btf_struct_access() callbacks, we miss rejecting
unstrusted BTF pointer writes. Fix and add a selftest for coverage.

Changelog:
----------
v1 -> v2
v1: https://lore.kernel.org/bpf/20260707190214.1997705-1-memxor@gmail.com

 * Add missing fixes tag.
 * Add Amery's acks.
====================

Link: https://patch.msgid.link/20260708030752.2503467-1-memxor@gmail.com
Signed-off-by: Eduard Zingerman <eddyz87@gmail.com>