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

Official description

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.

Affected packages & fixed versions

Affected products (as reported)

References

• https://git.kernel.org/stable/c/2411c02d03892a5057499f8102d0cc1e0f852416
• https://git.kernel.org/stable/c/944d671d5faa0d78980a3da5c0f04960ef1ad893