Use After Free Affecting kernel-default-devel package, versions <5.14.21-150500.55.73.1


Severity

Recommended
0.0
medium
0
10

Based on SUSE Linux Enterprise Server security rating.

Threat Intelligence

EPSS
0.04% (6th percentile)

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  • Snyk IDSNYK-SLES155-KERNELDEFAULTDEVEL-7697800
  • published17 Aug 2024
  • disclosed16 Aug 2024

Introduced: 16 Aug 2024

CVE-2022-48733  (opens in a new tab)
CWE-416  (opens in a new tab)

How to fix?

Upgrade SLES:15.5 kernel-default-devel to version 5.14.21-150500.55.73.1 or higher.

NVD Description

Note: Versions mentioned in the description apply only to the upstream kernel-default-devel package and not the kernel-default-devel package as distributed by SLES. See How to fix? for SLES:15.5 relevant fixed versions and status.

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.

CVSS Scores

version 3.1