CVE-2025-21810: driver core: class: Fix wild pointer dereferences in API class_dev_iter_next()

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

driver core: class: Fix wild pointer dereferences in API classdeviternext()

There are a potential wild pointer dereferences issue regarding APIs classdeviter(init|next|exit)(), as explained by below typical usage:

// All members of @iter are wild pointers. struct classdeviter iter;

// classdeviterinit(@iter, @class, ...) checks parameter @class for // potential classtosubsys() error, and it returns void type and does // not initialize its output parameter @iter, so caller can not detect // the error and continues to invoke classdeviternext(@iter) even if // @iter still contains wild pointers. classdeviterinit(&iter, ...);

// Dereference these wild pointers in @iter here once suffer the error. while (dev = classdeviternext(&iter)) { ... };

// Also dereference these wild pointers here. classdeviterexit(&iter);

Actually, all callers of these APIs have such usage pattern in kernel tree. Fix by: - Initialize output parameter @iter by memset() in classdeviterinit() and give callers prompt by prcrit() for the error. - Check if @iter is valid in classdeviternext().