CVE-2026-68138

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.