--- id: CVE-2026-74267 title: >- net/sched: sch_codel: Do not call qdisc_tree_reduce_backlog during peek before restoring qlen summary: >- 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_back… severity: critical cvss: 9.8 cvssVector: 'CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H' cvssSource: cna vendor: Linux product: Linux affected: - >- Linux >= cc71a757da78dd4aa1b4a9b19cb011833730ccf2 < bb9cfd874ee884117b33e92a002b9a45b48202f4 - >- Linux >= eda741fe155ddf5ecd2dd3bfbd4fc3c0c7dbb450 < 7a05af7f58566682b73578b72ca8e53a268c43bd - >- Linux >= 829c49b6b2ff45b043739168fd1245e4e1a91a30 < eba49fd85995a3851c597fa2d214f8d21736e1d8 - >- Linux >= 2f9761a94bae33d26e6a81b31b36e7d776d93dc1 < e8c6dbadf139cb14ea6ed14add6ed6e88504dedd - >- Linux >= 4d55144b12e742404bb3f8fee6038bafbf45619d < e4615aa6bb7802944ae790cb4b3ef8c1b7491af3 - >- Linux >= 342debc12183b51773b3345ba267e9263bdfaaef < 755108bb7a5083e911294c416cfea605dc75632f - >- Linux >= 342debc12183b51773b3345ba267e9263bdfaaef < 91e0a793a72374c20ab31a40ccec21373e82e973 - >- Linux >= 342debc12183b51773b3345ba267e9263bdfaaef < 52f1da34c9f4d5bdc1e8b44242da5c7ba8db85f3 - Linux 7a742a9506849d1c1aa71e36c89855ceddc7d58e - Linux e73c838c80dccb9e4f19becc11d9f3cb4a27d483 - Linux a57fe60ef4cf96bfbb6b58397ec28bdb5a5c6b31 - Linux >= 5.10.241 < 5.10.261 - Linux >= 5.15.190 < 5.15.212 - Linux >= 6.1.135 < 6.1.178 - Linux >= 6.6.88 < 6.6.145 - Linux >= 6.12.24 < 6.12.97 - Linux >= 5.4.297 < 5.5 - Linux >= 6.13.12 < 6.14 - Linux >= 6.14.3 < 6.15 - Linux 6.15 ssvc: exploitation: none automatable: 'yes' technicalImpact: total timestamp: '2026-10-16T18:51:44.190573Z' published: '2026-08-15' updated: '2026-10-16' sourceUpdated: '2026-10-16T18:55:28.845Z' source: CVEORG sourceUrl: 'https://www.cve.org/CVERecord?id=CVE-2026-74267' references: - url: 'https://git.kernel.org/stable/c/bb9cfd874ee884117b33e92a002b9a45b48202f4' - url: 'https://git.kernel.org/stable/c/7a05af7f58566682b73578b72ca8e53a268c43bd' - url: 'https://git.kernel.org/stable/c/eba49fd85995a3851c597fa2d214f8d21736e1d8' - url: 'https://git.kernel.org/stable/c/e8c6dbadf139cb14ea6ed14add6ed6e88504dedd' - url: 'https://git.kernel.org/stable/c/e4615aa6bb7802944ae790cb4b3ef8c1b7491af3' - url: 'https://git.kernel.org/stable/c/755108bb7a5083e911294c416cfea605dc75632f' - url: 'https://git.kernel.org/stable/c/91e0a793a72374c20ab31a40ccec21373e82e973' - url: 'https://git.kernel.org/stable/c/52f1da34c9f4d5bdc1e8b44242da5c7ba8db85f3' tags: - cve.org epss: 0.00714 epssPercentile: 0.52734 ingestedAt: '2026-10-16T19:46:24.387Z' --- ## Overview 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. ## Affected - `Linux >= cc71a757da78dd4aa1b4a9b19cb011833730ccf2 < bb9cfd874ee884117b33e92a002b9a45b48202f4` - `Linux >= eda741fe155ddf5ecd2dd3bfbd4fc3c0c7dbb450 < 7a05af7f58566682b73578b72ca8e53a268c43bd` - `Linux >= 829c49b6b2ff45b043739168fd1245e4e1a91a30 < eba49fd85995a3851c597fa2d214f8d21736e1d8` - `Linux >= 2f9761a94bae33d26e6a81b31b36e7d776d93dc1 < e8c6dbadf139cb14ea6ed14add6ed6e88504dedd` - `Linux >= 4d55144b12e742404bb3f8fee6038bafbf45619d < e4615aa6bb7802944ae790cb4b3ef8c1b7491af3` - `Linux >= 342debc12183b51773b3345ba267e9263bdfaaef < 755108bb7a5083e911294c416cfea605dc75632f` - `Linux >= 342debc12183b51773b3345ba267e9263bdfaaef < 91e0a793a72374c20ab31a40ccec21373e82e973` - `Linux >= 342debc12183b51773b3345ba267e9263bdfaaef < 52f1da34c9f4d5bdc1e8b44242da5c7ba8db85f3` - `Linux 7a742a9506849d1c1aa71e36c89855ceddc7d58e` - `Linux e73c838c80dccb9e4f19becc11d9f3cb4a27d483` - `Linux a57fe60ef4cf96bfbb6b58397ec28bdb5a5c6b31` - `Linux >= 5.10.241 < 5.10.261` - `Linux >= 5.15.190 < 5.15.212` - `Linux >= 6.1.135 < 6.1.178` - `Linux >= 6.6.88 < 6.6.145` - `Linux >= 6.12.24 < 6.12.97` - `Linux >= 5.4.297 < 5.5` - `Linux >= 6.13.12 < 6.14` - `Linux >= 6.14.3 < 6.15` - `Linux 6.15` ## Remediation Refer to the linked advisories for vendor-supplied fixes and affected version ranges.