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

Severity: medium (CVSS 5.5 v3.1)
Exploited in the wild: not listed in CISA KEV
EPSS: 0.1% probability of exploitation in the next 30 days
Public exploit or detection template: none known
Published: 2026-03-18 · updated 2026-10-15

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.

Affected products

Linux kernel: from 2.6.12.1 before 6.6.136; from 6.7 before 6.12.80; from 6.13 before 6.18.10; 2.6.12, 2.6.12-rc2, 2.6.12-rc3, 2.6.12-rc4, 2.6.12-rc5, 6.19-rc1 (+7) — fixed in 6.12.80, 6.18.10, 6.6.136

How to fix

Upgrade to a fixed version: Linux kernel 6.12.80, 6.18.10, 6.6.136. Check the vendor advisory for mitigations.

References

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