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

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

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

// class_dev_iter_init(@iter, @class, ...) checks parameter @class for
// potential class_to_subsys() 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 class_dev_iter_next(@iter) even if
// @iter still contains wild pointers.
class_dev_iter_init(&iter, ...);

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

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

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

Fixes: 7b884b7f24b4 ("driver core: class.c: convert to only use class_to_subsys")
Reviewed-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>
Signed-off-by: Zijun Hu <quic_zijuhu@quicinc.com>
Link: https://lore.kernel.org/r/20250105-class_fix-v6-1-3a2f1768d4d4@quicinc.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/drivers/base/class.c b/drivers/base/class.c
index 582b5a02a5c410113326601fe00eb6d7231f988f..d57f277978dc9033fba3484b4620bcf884a4029f 100644 (file)
--- a/drivers/base/class.c
+++ b/drivers/base/class.c
@@ -323,8 +323,12 @@ void class_dev_iter_init(struct class_dev_iter *iter, const struct class *class,
        struct subsys_private *sp = class_to_subsys(class);
        struct klist_node *start_knode = NULL;
 
-       if (!sp)
+       memset(iter, 0, sizeof(*iter));
+       if (!sp) {
+               pr_crit("%s: class %p was not registered yet\n",
+                       __func__, class);
                return;
+       }
 
        if (start)
                start_knode = &start->p->knode_class;
@@ -351,6 +355,9 @@ struct device *class_dev_iter_next(struct class_dev_iter *iter)
        struct klist_node *knode;
        struct device *dev;
 
+       if (!iter->sp)
+               return NULL;
+
        while (1) {
                knode = klist_next(&iter->ki);
                if (!knode)