# CVE-2022-49834: linux: In the Linux kernel, the following vulnerability has been resolved:  nilfs2: fix use-after-free bug of ns_writer on r...

CVE-2022-49834 is fixed in linux on 1 platform, first by DEBIAN-CVE-2022-49834, released May 1, 2025. It is not reported as exploited. Patch Radar priority: High.

- Web page: https://patchblox.com/security/cve/CVE-2022-49834
- Priority: High
- CVSS: 7.8 (high)
- EPSS: 0.0022
- CISA KEV: not listed
- Exploited (vendor report): no
- Publicly disclosed: no
- Published: May 1, 2025

## 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.

## Where it's fixed

| Platform | Product | Fixed in | Fix | Released |
|---|---|---|---|---|
| Linux | linux Debian 12.15 (bookworm) | 6.0.10-1 | [DEBIAN-CVE-2022-49834](https://patchblox.com/security/data/fix/linux/debian-cve-2022-49834.md) | May 1, 2025 |
| Linux | linux Debian 13.5 (trixie) | 6.0.10-1 | [DEBIAN-CVE-2022-49834](https://patchblox.com/security/data/fix/linux/debian-cve-2022-49834.md) | May 1, 2025 |
| Linux | linux Debian 14 | 6.0.10-1 | [DEBIAN-CVE-2022-49834](https://patchblox.com/security/data/fix/linux/debian-cve-2022-49834.md) | May 1, 2025 |

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