CVE-2022-49834: linux kernel Use-After-Free — Fix

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.

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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	< 4.9.334
linux	linux_kernel	4.10 — 4.14.300
linux	linux_kernel	4.15 — 4.19.267
linux	linux_kernel	4.20 — 5.4.225
linux	linux_kernel	5.5 — 5.10.155
linux	linux_kernel	5.11 — 5.15.79
linux	linux_kernel	5.16 — 6.0.9
linux	linux_kernel	All
linux	linux_kernel	All
linux	linux_kernel	All
linux	linux_kernel	All

References

Advisories & Patches

https://git.kernel.org/stable/c/39a3ed68270b079c6b874d4e4727a512b9b4882c https://git.kernel.org/stable/c/4feedde5486c07ea79787839153a71ca71329c7d https://git.kernel.org/stable/c/8cccf05fe857a18ee26e20d11a8455a73ffd4efd https://git.kernel.org/stable/c/9b162e81045266a2d5b44df9dffdf05c54de9cca https://git.kernel.org/stable/c/afbd1188382a75f6cfe22c0b68533f7f9664f182 https://git.kernel.org/stable/c/b152300d5a1ba4258dacf9916bff20e6a8c7603b https://git.kernel.org/stable/c/b2fbf10040216ef5ee270773755fc2f5da65b749 https://git.kernel.org/stable/c/b4736ab5542112fe0a40f140a0a0b072954f34da

Frequently Asked Questions

What is CVE-2022-49834? +

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

How severe is CVE-2022-49834? +

CVE-2022-49834 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-2022-49834? +

CVE-2022-49834 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-2022-49834? +

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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