CVE-2026-99222: keys: Protect the read method check against type removal

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

keys: Protect the read method check against type removal

keyctlreadkey() checks key->type->read without holding key->sem. A reference keeps the key alive, but does not pin the module containing its type. A surviving RxRPC key can therefore be read while AFRXRPC is being unloaded:

KEYCTLREAD task Module unload and key GC ---------------- ------------------------ lookupuserkey() permission / possession checks load key->type afrxrpcexit() unregisterkeytype() GC: downwrite(key->sem) GC: retype to keytypedead GC: upwrite(key->sem) unregisterkeytype() returns freemodule() read saved type's read member

The final access can read freed module storage. The read invocation in keyctlreadkey() is already protected by key->sem, but the earlier method check is outside that critical section.

Move the method check into keyctlreadkey(), after keyvalidate() and under its existing read hold on key->sem. The check and invocation then use the same protected type for length queries and every read retry. The GC cannot retype the key until the semaphore is released, and type unregistration waits for that GC pass before the module can be freed.

Return -EOPNOTSUPP when validation succeeds and the type has no read method. A temporary buffer may now be allocated before this result; allocation and copying to userspace remain outside the semaphore.