CVE-2022-48733: linux kernel Use-After-Free — Fix

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.

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CVSS v3.1 Score

7.8

HIGH

CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H

Weakness Type (CWE)

CWE-416 Use After Free

Affected Products

Vendor	Product	Versions
linux	linux_kernel	< 5.10.226
linux	linux_kernel	5.11 — 5.15.22
linux	linux_kernel	5.16 — 5.16.8
linux	linux_kernel	All
linux	linux_kernel	All

References

Advisories & Patches

https://git.kernel.org/stable/c/28b21c558a3753171097193b6f6602a94169093a https://git.kernel.org/stable/c/7e4c72dbaf62f8978af8321a24dbd35566d3a78a https://git.kernel.org/stable/c/9372fa1d73da5f1673921e365d0cd2c27ec7adc2 https://git.kernel.org/stable/c/a7b717fa15165d3d9245614680bebc48a52ac05d https://git.kernel.org/stable/c/28b21c558a3753171097193b6f6602a94169093a https://git.kernel.org/stable/c/9372fa1d73da5f1673921e365d0cd2c27ec7adc2 https://git.kernel.org/stable/c/a7b717fa15165d3d9245614680bebc48a52ac05d

Other References

https://lists.debian.org/debian-lts-announce/2024/10/msg00003.html

Frequently Asked Questions

What is CVE-2022-48733? +

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. It has a CVSS v3.1 base score of 7.8 (HIGH).

How severe is CVE-2022-48733? +

CVE-2022-48733 has a CVSS v3.1 score of 7.8 out of 10, rated HIGH. This is a high-severity vulnerability that should be prioritized for patching.

What products are affected by CVE-2022-48733? +

CVE-2022-48733 affects products from linux, specifically: linux_kernel. Check the affected products table above for specific version ranges.

How do I check if I'm vulnerable to CVE-2022-48733? +

You can use Secably's free Website Scanner to check your website for known vulnerabilities. For infrastructure scanning, use the Port Scanner to identify exposed services that may be affected. Check the vendor advisories linked above for specific patch and version information.

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