CVE-2021-47125 sch_htb: fix refcount leak in htb_parent_to_leaf_offload
A refcount leak in the Linux kernel's HTB scheduler can lead to resource exhaustion and denial of service.
- Exploited in the wild
- Not known
- Login needed
- Any signed-in user
- Attackable
- Local or same network only
- Victim action needed
- Not needed
- Fix
- None listed
What is CVE-2021-47125?
CVE-2021-47125 is a medium-severity memory corruption vulnerability in Linux kernel, published on 15 Mar 2024. It can only be exploited from the same machine or local network, with no action from the victim.
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.
Which versions are affected by CVE-2021-47125?
It affects 1 product.
Products include Linux kernel.
How do I fix CVE-2021-47125?
No fix has been published for CVE-2021-47125 yet. Limit exposure of the affected software until one is available.
Upgrade to the fixed version. Memory-safe languages, compiler hardening and fuzzing prevent most new cases. More about Memory corruption.
Is CVE-2021-47125 being exploited?
There is no known exploitation of CVE-2021-47125 in the wild and no public exploit code.
Other vulnerabilities in Linux kernel
Sources
Also known as GHSA-6297-42q7-j694, UBUNTU-CVE-2021-47125.