CVE-2021-47125: sch_htb: fix refcount leak in htb_parent_to_leaf_offload

First published: Fri Mar 15 2024(Updated: )

In the Linux kernel, the following vulnerability has been resolved: sch_htb: fix refcount leak in htb_parent_to_leaf_offload The commit ae81feb7338c ("sch_htb: fix null pointer dereference on a null new_q") fixes a NULL pointer dereference bug, but it is not correct. Because htb_graft_helper properly handles the case when new_q is NULL, and after the previous patch by skipping this call which creates an inconsistency : dev_queue->qdisc will still point to the old qdisc, but cl->parent->leaf.q will point to the new one (which will be noop_qdisc, because new_q was NULL). The code is based on an assumption that these two pointers are the same, so it can lead to refcount leaks. The correct fix is to add a NULL pointer check to protect qdisc_refcount_inc inside htb_parent_to_leaf_offload.

Credit: 416baaa9-dc9f-4396-8d5f-8c081fb06d67

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