CVE-2022-49834 nilfs2: fix use-after-free bug of ns_writer on remount
A use-after-free vulnerability in the Linux kernel nilfs2 filesystem allows attackers to execute arbitrary code or escalate privileges via remount operations.
- Exploited in the wild
- Not known
- Login needed
- Any signed-in user
- Attackable
- Local or same network only
- Victim action needed
- Not needed
- Fix
- Available
What is CVE-2022-49834?
CVE-2022-49834 is a high-severity use after free vulnerability in Linux kernel, published on 1 May 2025. 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:
nilfs2: fix use-after-free bug of ns_writer on remount
If a nilfs2 filesystem is downgraded to read-only due to metadata corruption on disk and is remounted read/write, or if emergency read-only remount is performed, detaching a log writer and synchronizing the filesystem can be done at the same time.
In these cases, use-after-free of the log writer (hereinafter nilfs->ns_writer) can happen as shown in the scenario below:
Task1 Task2 -------------------------------- ------------------------------ nilfs_construct_segment nilfs_segctor_sync init_wait init_waitqueue_entry add_wait_queue schedule nilfs_remount (R/W remount case) nilfs_attach_log_writer nilfs_detach_log_writer nilfs_segctor_destroy kfree finish_wait _raw_spin_lock_irqsave __raw_spin_lock_irqsave do_raw_spin_lock debug_spin_lock_before <-- use-after-free
While Task1 is sleeping, nilfs->ns_writer is freed by Task2. After Task1 waked up, Task1 accesses nilfs->ns_writer which is already freed. This scenario diagram is based on the Shigeru Yoshida's post [1].
This patch fixes the issue by not detaching nilfs->ns_writer on remount so that this UAF race doesn't happen. Along with this change, this patch also inserts a few necessary read-only checks with superblock instance where only the ns_writer pointer was used to check if the filesystem is read-only.
Weakness: CWE-416
Which versions are affected by CVE-2022-49834?
It affects 1 product.
Products include Linux kernel.
How do I fix CVE-2022-49834?
Apply the vendor's patch.
Upgrade to the fixed version. These bugs are found with fuzzing and sanitisers and avoided by memory-safe languages. More about Use after free.
Is CVE-2022-49834 being exploited?
There is no known exploitation of CVE-2022-49834 in the wild and no public exploit code.
Other vulnerabilities in Linux kernel
Sources
Also known as DEBIAN-CVE-2022-49834, GHSA-7jwj-6g7w-4c9q, UBUNTU-CVE-2022-49834.