CVE-2026-64027

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

net: shaper: rework the VALID marking (again)

Recent commit changed the semantics from NOT_VALID to VALID.

I didn't realize that the flags are not stored atomically

with the entry in XArray. There's still a race of reader

observing a VALID mark for a slot, getting interrupted,

writer replacing the entry with a different one, reader

continuing, fetching the entry which is now a different

pointer than the pointer for which VALID was meant.

The biggest consequence of this is that we may see a UAF

since net_shaper_rollback() assumed that entries without

VALID can be freed without observing RCU.

Looks like the XArray marks are buying us nothing at this

point. Let's convert the code to an explicit valid field.

The smp_load_acquire() / smp_store_release() barriers are

marginally cleaner.