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cve/cves/2026/CVE-2026-68138.md
0xMarcio 08d697bd12 Carry each record's title, vendor and product, and search them first
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2026-09-04 02:32:22 +02:00

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Markdown

### [CVE-2026-68138](https://www.cve.org/CVERecord?id=CVE-2026-68138)
**net/sched: serialize qdisc_rtab_list against concurrent get/put**
![](https://img.shields.io/static/v1?label=Vendor&message=Linux&color=blue)
![](https://img.shields.io/static/v1?label=Product&message=Linux&color=blue)
![](https://img.shields.io/static/v1?label=Version&message=470502de5bdb1ed0def643a4458593a40b8f6b66&color=brightgreen)
![](https://img.shields.io/static/v1?label=Version&message=5.1&color=brightgreen)
![](https://img.shields.io/static/v1?label=Vulnerability&message=n%2Fa&color=blue)
### 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.
### POC
#### Reference
No PoCs from references.
#### Github
- https://github.com/aramosf/CVE-2026-68138
- https://github.com/suominen/CVE-2026-68138
- https://github.com/jangkrikkbozz/CVE-2026-68138