CVE-2022-48733 btrfs: fix use-after-free after failure to create a snapshot
A use-after-free in the Linux kernel btrfs filesystem allows local attackers to potentially execute code or escalate privileges via snapshot creation failures.
- 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-2022-48733?
CVE-2022-48733 is a high-severity use after free vulnerability in Linux kernel, published on 20 Jun 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:
btrfs: fix use-after-free after failure to create a snapshot
At ioctl.c:create_snapshot(), we allocate a pending snapshot structure and then attach it to the transaction's list of pending snapshots. After that we call btrfs_commit_transaction(), and if that returns an error we jump to 'fail' label, where we kfree() the pending snapshot structure. This can result in a later use-after-free of the pending snapshot:
1) We allocated the pending snapshot and added it to the transaction's list of pending snapshots;
2) We call btrfs_commit_transaction(), and it fails either at the first call to btrfs_run_delayed_refs() or btrfs_start_dirty_block_groups(). In both cases, we don't abort the transaction and we release our transaction handle. We jump to the 'fail' label and free the pending snapshot structure. We return with the pending snapshot still in the transaction's list;
3) Another task commits the transaction. This time there's no error at all, and then during the transaction commit it accesses a pointer to the pending snapshot structure that the snapshot creation task has already freed, resulting in a user-after-free.
This issue could actually be detected by smatch, which produced the following warning:
fs/btrfs/ioctl.c:843 create_snapshot() warn: '&pending_snapshot->list' not removed from list
So fix this by not having the snapshot creation ioctl directly add the pending snapshot to the transaction's list. Instead add the pending snapshot to the transaction handle, and then at btrfs_commit_transaction() we add the snapshot to the list only when we can guarantee that any error returned after that point will result in a transaction abort, in which case the ioctl code can safely free the pending snapshot and no one can access it anymore.
Weakness: CWE-416
Which versions are affected by CVE-2022-48733?
It affects 1 product.
Products include Linux kernel.
How do I fix CVE-2022-48733?
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-2022-48733 being exploited?
There is no known exploitation of CVE-2022-48733 in the wild and no public exploit code.
Other vulnerabilities in Linux kernel
Sources
Also known as DEBIAN-CVE-2022-48733, GHSA-grhv-62hf-9jg3, UBUNTU-CVE-2022-48733.