CVE-2026-74267

net/sched: sch_codel: Do not call qdisc_tree_reduce_backlog during peek before restoring qlen

State: Published
Severity: 9.8 Critical
Published: Aug 15, 2026
Updated: Oct 16, 2026
Reserved: Aug 15, 2026

Description

In the Linux kernel, the following vulnerability has been resolved:

net/sched: sch_codel: Do not call qdisc_tree_reduce_backlog during peek before restoring qlen

Whenever codel drops packets during peek, it calls qdisc_tree_reduce_backlog. An issue arises because it calls qdisc_tree_reduce_backlog before it reincrements the qlen. If qlen drops to zero, but peek returns an skb, the parent's qlen_notify callback will be executed even though codel still has 1 packet on the queue and, thus, will mistakenly deactivate the parent's class causing issues like a wild memory access when qfq has codel as a child:

[ 36.339843][ T370] Oops: general protection fault, probably for non-canonical address 0xfbd59c0000000024: 0000 [#1] SMP KASAN NOPTI [ 36.340408][ T370] KASAN: maybe wild-memory-access in range [0xdead000000000120-0xdead000000000127] [ 36.340737][ T370] CPU: 2 UID: 0 PID: 370 Comm: tc Not tainted 7.1.0-rc5-00287-g66e13b626592 #87 PREEMPT(full) [ 36.341113][ T370] Hardware name: Bochs Bochs, BIOS Bochs 01/01/2011 [ 36.341357][ T370] RIP: 0010:qfq_deactivate_agg (include/linux/list.h:1029 (discriminator 2) include/linux/list.h:1043 (discriminator 2) net/sched/sch_qfq.c:1369 (discriminator 2) net/sched/sch_qfq.c:1395 (discriminator 2)) sch_qfq [ 36.342221][ T370] RSP: 0018:ffff8881100ef370 EFLAGS: 00010216 [ 36.342422][ T370] RAX: 0000000000000000 RBX: ffff8881058a9568 RCX: dffffc0000000000 [ 36.342664][ T370] RDX: 1ffff11021064dc3 RSI: ffff888108326e00 RDI: dffffc0000000000 [ 36.342905][ T370] RBP: ffff8881058a8280 R08: dead000000000122 R09: 1bd5a00000000024 [ 36.343140][ T370] R10: fffffbfff2940329 R11: fffffbfff2940329 R12: 0000000000000000 [ 36.343383][ T370] R13: dead000000000100 R14: ffff8881058a9580 R15: ffff8881058a9578 [ 36.343631][ T370] FS: 00007fc04b0ca780(0000) GS:ffff888184fef000(0000) knlGS:0000000000000000 [ 36.343911][ T370] CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 [ 36.344116][ T370] CR2: 0000557c02c02000 CR3: 000000010e0ba000 CR4: 0000000000750ef0 [ 36.344359][ T370] PKRU: 55555554 [ 36.344481][ T370] Call Trace: ... [ 36.345054][ T370] qfq_reset_qdisc (net/sched/sch_qfq.c:357 net/sched/sch_qfq.c:1487) sch_qfq [ 36.345222][ T370] qdisc_reset (net/sched/sch_generic.c:1057) [ 36.345503][ T370] __qdisc_destroy (net/sched/sch_generic.c:1096) [ 36.345677][ T370] qdisc_graft (net/sched/sch_api.c:1062 net/sched/sch_api.c:1053 net/sched/sch_api.c:1159) [ 36.346335][ T370] tc_get_qdisc (net/sched/sch_api.c:1528 net/sched/sch_api.c:1556)

Fix this by only calling qdisc_tree_reduce_backlog in peek after the qlen is restored.

Scores

CVSS	Score	Vector	Source
3.1	9.8 Critical	CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H	Linux

Weaknesses

The record names no weakness.

Affected Products

Product	Versions
LinuxLinux	cc71a757da78dd4aa1b4a9b19cb011833730ccf2 to before bb9cfd874ee884117b33e92a002b9a45b48202f4Affected eda741fe155ddf5ecd2dd3bfbd4fc3c0c7dbb450 to before 7a05af7f58566682b73578b72ca8e53a268c43bdAffected 829c49b6b2ff45b043739168fd1245e4e1a91a30 to before eba49fd85995a3851c597fa2d214f8d21736e1d8Affected 2f9761a94bae33d26e6a81b31b36e7d776d93dc1 to before e8c6dbadf139cb14ea6ed14add6ed6e88504deddAffected 4d55144b12e742404bb3f8fee6038bafbf45619d to before e4615aa6bb7802944ae790cb4b3ef8c1b7491af3Affected 342debc12183b51773b3345ba267e9263bdfaaef to before 755108bb7a5083e911294c416cfea605dc75632fAffected 342debc12183b51773b3345ba267e9263bdfaaef to before 91e0a793a72374c20ab31a40ccec21373e82e973Affected 342debc12183b51773b3345ba267e9263bdfaaef to before 52f1da34c9f4d5bdc1e8b44242da5c7ba8db85f3Affected 7a742a9506849d1c1aa71e36c89855ceddc7d58eAffected e73c838c80dccb9e4f19becc11d9f3cb4a27d483Affected a57fe60ef4cf96bfbb6b58397ec28bdb5a5c6b31Affected 5.10.241 to before 5.10.261Affected 5.15.190 to before 5.15.212Affected 6.1.135 to before 6.1.178Affected 6.6.88 to before 6.6.145Affected 6.12.24 to before 6.12.97Affected 5.4.297 to before 5.5Affected 6.13.12 to before 6.14Affected 6.14.3 to before 6.15Affected
LinuxLinux	6.15Affected before 6.15Not affected 5.10.261 through 5.10.Not affected 5.15.212 through 5.15.Not affected 6.1.178 through 6.1.Not affected 6.6.145 through 6.6.Not affected 6.12.97 through 6.12.Not affected 6.18.40 through 6.18.Not affected 7.1.5 through 7.1.*Not affected 7.2 and laterNot affected

Product

Versions

LinuxLinux

cc71a757da78dd4aa1b4a9b19cb011833730ccf2 to before bb9cfd874ee884117b33e92a002b9a45b48202f4Affected
eda741fe155ddf5ecd2dd3bfbd4fc3c0c7dbb450 to before 7a05af7f58566682b73578b72ca8e53a268c43bdAffected
829c49b6b2ff45b043739168fd1245e4e1a91a30 to before eba49fd85995a3851c597fa2d214f8d21736e1d8Affected
2f9761a94bae33d26e6a81b31b36e7d776d93dc1 to before e8c6dbadf139cb14ea6ed14add6ed6e88504deddAffected
4d55144b12e742404bb3f8fee6038bafbf45619d to before e4615aa6bb7802944ae790cb4b3ef8c1b7491af3Affected
342debc12183b51773b3345ba267e9263bdfaaef to before 755108bb7a5083e911294c416cfea605dc75632fAffected
342debc12183b51773b3345ba267e9263bdfaaef to before 91e0a793a72374c20ab31a40ccec21373e82e973Affected
342debc12183b51773b3345ba267e9263bdfaaef to before 52f1da34c9f4d5bdc1e8b44242da5c7ba8db85f3Affected
7a742a9506849d1c1aa71e36c89855ceddc7d58eAffected
e73c838c80dccb9e4f19becc11d9f3cb4a27d483Affected
a57fe60ef4cf96bfbb6b58397ec28bdb5a5c6b31Affected
5.10.241 to before 5.10.261Affected
5.15.190 to before 5.15.212Affected
6.1.135 to before 6.1.178Affected
6.6.88 to before 6.6.145Affected
6.12.24 to before 6.12.97Affected
5.4.297 to before 5.5Affected
6.13.12 to before 6.14Affected
6.14.3 to before 6.15Affected

LinuxLinux

6.15Affected
before 6.15Not affected
5.10.261 through 5.10.*Not affected
5.15.212 through 5.15.*Not affected
6.1.178 through 6.1.*Not affected
6.6.145 through 6.6.*Not affected
6.12.97 through 6.12.*Not affected
6.18.40 through 6.18.*Not affected
7.1.5 through 7.1.*Not affected
7.2 and laterNot affected

References

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