CVE-2021-4150

What it actually does

Use-after-free in add_partition within block/partitions/core.c triggered when device_add fails, allowing a local user to cause kernel memory corruption leading to denial of service.

Why it matters to the business

Local users can crash affected Linux systems, resulting in unplanned downtime and loss of availability for workloads running on unpatched kernels.

How an attack unfolds

A local attacker with user privileges crafts a scenario where adding a partition causes device_add to fail; the missing cleanup leaves a dangling pointer that is later dereferenced, crashing the kernel. No remote or privileged escalation path is described.

How to fix it

Upgrade the Linux kernel to the commit 8bb7eca972ad531c9b149c0a51ab43a417385813 or later; apply vendor-supplied kernel updates that contain the fix for the add_partition cleanup path.

How to confirm the fix worked

Verify the running kernel contains commit 8bb7eca972ad531c9b149c0a51ab43a417385813; confirm absence of the vulnerable add_partition code path via source inspection or kernel version checks against fixed releases.

Typical attack path

1. Obtain local user access on a vulnerable Linux system
2. Trigger partition addition that forces device_add to fail
3. Cause subsequent dereference of the freed structure
4. Induce kernel panic or system hang

How to detect it

Review kernel logs for oops or panic messages referencing add_partition, device_add failures, or block partition code paths around the time of unexpected reboots or hangs.

What your security team should do

• Prioritize kernel updates on all Linux systems reachable by untrusted local users
• Restrict unprivileged local access where possible until patches are applied
• Monitor for kernel oops or panic events related to block device partition handling