{"id":"CVE-2026-80630","state":"PUBLISHED","title":"net/sched: sch_fq_codel: Do not call qdisc_tree_reduce_backlog during peek before restoring qlen","description":"In the Linux kernel, the following vulnerability has been resolved:\n\nnet/sched: sch_fq_codel: Do not call qdisc_tree_reduce_backlog during peek before restoring qlen\n\nWhenever fq_codel drops packets during peek, it calls\nqdisc_tree_reduce_backlog. An issue arises because it calls\nqdisc_tree_reduce_backlog before it reincrements the qlen. If qlen drops\nto zero, but peek returns an skb, the parent's qlen_notify callback will be\nexecuted even though fq_codel still has 1 packet on the queue and, thus,\nwill mistakenly deactivate the parent's class causing issues like a recent\nreport [1] and a wild memory access in qfq:\n\n[   29.371146][  T360] Oops: general protection fault, probably for non-canonical address 0xfbd59c0000000024: 0000 [#1] SMP KASAN NOPTI\n[   29.371666][  T360] KASAN: maybe wild-memory-access in range [0xdead000000000120-0xdead000000000127]\n[   29.371987][  T360] CPU: 6 UID: 0 PID: 360 Comm: tc Not tainted 7.1.0-rc5-00285-gc530e5b2dbc6-dirty #82 PREEMPT(full)\n[   29.372384][  T360] Hardware name: Bochs Bochs, BIOS Bochs 01/01/2011\n[   29.372620][  T360] 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\n[   29.373544][  T360] RSP: 0018:ffff888102417370 EFLAGS: 00010216\n[   29.373800][  T360] RAX: 0000000000000000 RBX: ffff88811224d568 RCX: dffffc0000000000\n[   29.374079][  T360] RDX: 1ffff11021fe1543 RSI: ffff88810ff0aa00 RDI: dffffc0000000000\n[   29.374368][  T360] RBP: ffff88811224c280 R08: dead000000000122 R09: 1bd5a00000000024\n[   29.374649][  T360] R10: fffffbfff7940329 R11: fffffbfff7940329 R12: 0000000000000000\n[   29.374926][  T360] R13: dead000000000100 R14: ffff88811224d580 R15: ffff88811224d578\n[   29.375207][  T360] FS:  00007f5b794e5780(0000) GS:ffff88815d1e9000(0000) knlGS:0000000000000000\n[   29.375545][  T360] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033\n[   29.375823][  T360] CR2: 000055ffb091f000 CR3: 000000010a305000 CR4: 0000000000750ef0\n[   29.376103][  T360] PKRU: 55555554\n[   29.376258][  T360] Call Trace:\n[   29.376401][  T360]  <TASK>\n...\n[   29.376885][  T360] qfq_reset_qdisc (net/sched/sch_qfq.c:357 net/sched/sch_qfq.c:1487) sch_qfq\n[   29.377074][  T360]  qdisc_reset (net/sched/sch_generic.c:1057)\n[   29.377414][  T360]  __qdisc_destroy (net/sched/sch_generic.c:1096)\n[   29.377600][  T360]  qdisc_graft (net/sched/sch_api.c:1062 net/sched/sch_api.c:1053 net/sched/sch_api.c:1159)\n[   29.378593][  T360]  tc_get_qdisc (net/sched/sch_api.c:1528 net/sched/sch_api.c:1556)\n\nFix this by only calling qdisc_tree_reduce_backlog in peek after the\nqlen is restored.\n\n[1] http://lore.kernel.org/netdev/CAN2cbVe79oj0O9==m4+4x3v+O+qzRagA=2=wkrp9i9=CqYvyZA@mail.gmail.com/","publishedAt":"2026-08-28T06:48:46.569Z","updatedAt":"2026-10-16T19:26:31.257Z","severity":{"score":9.8,"label":"Critical","version":"3.1","vector":"CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H","source":"Linux"},"assigner":"Linux","products":["Linux Linux"],"affected":[{"vendor":"Linux","product":"Linux","defaultStatus":"unaffected","versions":[{"version":"cc71a757da78dd4aa1b4a9b19cb011833730ccf2","status":"affected","lessThan":"3e515188393e62a718ccebee651ee74514104ff6","versionType":"git"},{"version":"eda741fe155ddf5ecd2dd3bfbd4fc3c0c7dbb450","status":"affected","lessThan":"20dd591d8f951e1e6aca5052be8785e6181055e2","versionType":"git"},{"version":"829c49b6b2ff45b043739168fd1245e4e1a91a30","status":"affected","lessThan":"94a5f1efdefb01f82cd228bf4e7ef1e8fc075c80","versionType":"git"},{"version":"2f9761a94bae33d26e6a81b31b36e7d776d93dc1","status":"affected","lessThan":"acc08a0c7f37ebb1901144e03a7cba7d4afd9203","versionType":"git"},{"version":"4d55144b12e742404bb3f8fee6038bafbf45619d","status":"affected","lessThan":"7c09843fd2b44d9bf0de798683861d1aecd62a08","versionType":"git"},{"version":"342debc12183b51773b3345ba267e9263bdfaaef","status":"affected","lessThan":"0500af8630c3253f0dde879bd3a73a06bb2f2b3f","versionType":"git"},{"version":"342debc12183b51773b3345ba267e9263bdfaaef","status":"affected","lessThan":"af54df2f44d9605614bc7ed96640302a240a9a62","versionType":"git"},{"version":"342debc12183b51773b3345ba267e9263bdfaaef","status":"affected","lessThan":"097f6fc7b1ae362dd7a9444b2572162fda73b284","versionType":"git"},{"version":"7a742a9506849d1c1aa71e36c89855ceddc7d58e","status":"affected","versionType":"git"},{"version":"e73c838c80dccb9e4f19becc11d9f3cb4a27d483","status":"affected","versionType":"git"},{"version":"a57fe60ef4cf96bfbb6b58397ec28bdb5a5c6b31","status":"affected","versionType":"git"},{"version":"5.10.241","status":"affected","lessThan":"5.10.261","versionType":"semver"},{"version":"5.15.190","status":"affected","lessThan":"5.15.212","versionType":"semver"},{"version":"6.1.135","status":"affected","lessThan":"6.1.178","versionType":"semver"},{"version":"6.6.88","status":"affected","lessThan":"6.6.145","versionType":"semver"},{"version":"6.12.24","status":"affected","lessThan":"6.12.97","versionType":"semver"},{"version":"5.4.297","status":"affected","lessThan":"5.5","versionType":"semver"},{"version":"6.13.12","status":"affected","lessThan":"6.14","versionType":"semver"},{"version":"6.14.3","status":"affected","lessThan":"6.15","versionType":"semver"}],"repo":"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git","programFiles":["net/sched/sch_fq_codel.c"]},{"vendor":"Linux","product":"Linux","defaultStatus":"affected","versions":[{"version":"6.15","status":"affected"},{"version":"0","status":"unaffected","lessThan":"6.15","versionType":"semver"},{"version":"5.10.261","status":"unaffected","lessThanOrEqual":"5.10.*","versionType":"semver"},{"version":"5.15.212","status":"unaffected","lessThanOrEqual":"5.15.*","versionType":"semver"},{"version":"6.1.178","status":"unaffected","lessThanOrEqual":"6.1.*","versionType":"semver"},{"version":"6.6.145","status":"unaffected","lessThanOrEqual":"6.6.*","versionType":"semver"},{"version":"6.12.97","status":"unaffected","lessThanOrEqual":"6.12.*","versionType":"semver"},{"version":"6.18.40","status":"unaffected","lessThanOrEqual":"6.18.*","versionType":"semver"},{"version":"7.1.5","status":"unaffected","lessThanOrEqual":"7.1.*","versionType":"semver"},{"version":"7.2","status":"unaffected","lessThanOrEqual":"*","versionType":"original_commit_for_fix"}],"repo":"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git","programFiles":["net/sched/sch_fq_codel.c"]}],"references":["https://git.kernel.org/stable/c/3e515188393e62a718ccebee651ee74514104ff6","https://git.kernel.org/stable/c/20dd591d8f951e1e6aca5052be8785e6181055e2","https://git.kernel.org/stable/c/94a5f1efdefb01f82cd228bf4e7ef1e8fc075c80","https://git.kernel.org/stable/c/acc08a0c7f37ebb1901144e03a7cba7d4afd9203","https://git.kernel.org/stable/c/7c09843fd2b44d9bf0de798683861d1aecd62a08","https://git.kernel.org/stable/c/0500af8630c3253f0dde879bd3a73a06bb2f2b3f","https://git.kernel.org/stable/c/af54df2f44d9605614bc7ed96640302a240a9a62","https://git.kernel.org/stable/c/097f6fc7b1ae362dd7a9444b2572162fda73b284"],"weaknesses":[],"ingestedAt":"2026-10-29T20:13:07.220Z","source":{"repository":"CVEProject/cvelistV5","path":"cves/2026/80xxx/CVE-2026-80630.json","commit":"556c9d3a8cd17e218bb8e452ba7cd619a384ff47"},"raw":{"dataType":"CVE_RECORD","dataVersion":"5.2","cveMetadata":{"cveId":"CVE-2026-80630","state":"PUBLISHED","datePublished":"2026-08-28T06:48:46.569Z","dateUpdated":"2026-10-16T19:26:31.257Z","assignerShortName":"Linux","assignerOrgId":"416baaa9-dc9f-4396-8d5f-8c081fb06d67","dateReserved":"2026-08-26T14:34:25.776Z"},"containers":{"cna":{"title":"net/sched: sch_fq_codel: Do not call qdisc_tree_reduce_backlog during peek before restoring qlen","descriptions":[{"lang":"en","value":"In the Linux kernel, the following vulnerability has been resolved:\n\nnet/sched: sch_fq_codel: Do not call qdisc_tree_reduce_backlog during peek before restoring qlen\n\nWhenever fq_codel drops packets during peek, it calls\nqdisc_tree_reduce_backlog. An issue arises because it calls\nqdisc_tree_reduce_backlog before it reincrements the qlen. If qlen drops\nto zero, but peek returns an skb, the parent's qlen_notify callback will be\nexecuted even though fq_codel still has 1 packet on the queue and, thus,\nwill mistakenly deactivate the parent's class causing issues like a recent\nreport [1] and a wild memory access in qfq:\n\n[   29.371146][  T360] Oops: general protection fault, probably for non-canonical address 0xfbd59c0000000024: 0000 [#1] SMP KASAN NOPTI\n[   29.371666][  T360] KASAN: maybe wild-memory-access in range [0xdead000000000120-0xdead000000000127]\n[   29.371987][  T360] CPU: 6 UID: 0 PID: 360 Comm: tc Not tainted 7.1.0-rc5-00285-gc530e5b2dbc6-dirty #82 PREEMPT(full)\n[   29.372384][  T360] Hardware name: Bochs Bochs, BIOS Bochs 01/01/2011\n[   29.372620][  T360] 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\n[   29.373544][  T360] RSP: 0018:ffff888102417370 EFLAGS: 00010216\n[   29.373800][  T360] RAX: 0000000000000000 RBX: ffff88811224d568 RCX: dffffc0000000000\n[   29.374079][  T360] RDX: 1ffff11021fe1543 RSI: ffff88810ff0aa00 RDI: dffffc0000000000\n[   29.374368][  T360] RBP: ffff88811224c280 R08: dead000000000122 R09: 1bd5a00000000024\n[   29.374649][  T360] R10: fffffbfff7940329 R11: fffffbfff7940329 R12: 0000000000000000\n[   29.374926][  T360] R13: dead000000000100 R14: ffff88811224d580 R15: ffff88811224d578\n[   29.375207][  T360] FS:  00007f5b794e5780(0000) GS:ffff88815d1e9000(0000) knlGS:0000000000000000\n[   29.375545][  T360] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033\n[   29.375823][  T360] CR2: 000055ffb091f000 CR3: 000000010a305000 CR4: 0000000000750ef0\n[   29.376103][  T360] PKRU: 55555554\n[   29.376258][  T360] Call Trace:\n[   29.376401][  T360]  <TASK>\n...\n[   29.376885][  T360] qfq_reset_qdisc (net/sched/sch_qfq.c:357 net/sched/sch_qfq.c:1487) sch_qfq\n[   29.377074][  T360]  qdisc_reset (net/sched/sch_generic.c:1057)\n[   29.377414][  T360]  __qdisc_destroy (net/sched/sch_generic.c:1096)\n[   29.377600][  T360]  qdisc_graft (net/sched/sch_api.c:1062 net/sched/sch_api.c:1053 net/sched/sch_api.c:1159)\n[   29.378593][  T360]  tc_get_qdisc (net/sched/sch_api.c:1528 net/sched/sch_api.c:1556)\n\nFix this by only calling qdisc_tree_reduce_backlog in peek after the\nqlen is restored.\n\n[1] http://lore.kernel.org/netdev/CAN2cbVe79oj0O9==m4+4x3v+O+qzRagA=2=wkrp9i9=CqYvyZA@mail.gmail.com/"}],"affected":[{"vendor":"Linux","product":"Linux","defaultStatus":"unaffected","versions":[{"version":"cc71a757da78dd4aa1b4a9b19cb011833730ccf2","status":"affected","lessThan":"3e515188393e62a718ccebee651ee74514104ff6","versionType":"git"},{"version":"eda741fe155ddf5ecd2dd3bfbd4fc3c0c7dbb450","status":"affected","lessThan":"20dd591d8f951e1e6aca5052be8785e6181055e2","versionType":"git"},{"version":"829c49b6b2ff45b043739168fd1245e4e1a91a30","status":"affected","lessThan":"94a5f1efdefb01f82cd228bf4e7ef1e8fc075c80","versionType":"git"},{"version":"2f9761a94bae33d26e6a81b31b36e7d776d93dc1","status":"affected","lessThan":"acc08a0c7f37ebb1901144e03a7cba7d4afd9203","versionType":"git"},{"version":"4d55144b12e742404bb3f8fee6038bafbf45619d","status":"affected","lessThan":"7c09843fd2b44d9bf0de798683861d1aecd62a08","versionType":"git"},{"version":"342debc12183b51773b3345ba267e9263bdfaaef","status":"affected","lessThan":"0500af8630c3253f0dde879bd3a73a06bb2f2b3f","versionType":"git"},{"version":"342debc12183b51773b3345ba267e9263bdfaaef","status":"affected","lessThan":"af54df2f44d9605614bc7ed96640302a240a9a62","versionType":"git"},{"version":"342debc12183b51773b3345ba267e9263bdfaaef","status":"affected","lessThan":"097f6fc7b1ae362dd7a9444b2572162fda73b284","versionType":"git"},{"version":"7a742a9506849d1c1aa71e36c89855ceddc7d58e","status":"affected","versionType":"git"},{"version":"e73c838c80dccb9e4f19becc11d9f3cb4a27d483","status":"affected","versionType":"git"},{"version":"a57fe60ef4cf96bfbb6b58397ec28bdb5a5c6b31","status":"affected","versionType":"git"},{"version":"5.10.241","status":"affected","lessThan":"5.10.261","versionType":"semver"},{"version":"5.15.190","status":"affected","lessThan":"5.15.212","versionType":"semver"},{"version":"6.1.135","status":"affected","lessThan":"6.1.178","versionType":"semver"},{"version":"6.6.88","status":"affected","lessThan":"6.6.145","versionType":"semver"},{"version":"6.12.24","status":"affected","lessThan":"6.12.97","versionType":"semver"},{"version":"5.4.297","status":"affected","lessThan":"5.5","versionType":"semver"},{"version":"6.13.12","status":"affected","lessThan":"6.14","versionType":"semver"},{"version":"6.14.3","status":"affected","lessThan":"6.15","versionType":"semver"}],"repo":"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git","programFiles":["net/sched/sch_fq_codel.c"]},{"vendor":"Linux","product":"Linux","defaultStatus":"affected","versions":[{"version":"6.15","status":"affected"},{"version":"0","status":"unaffected","lessThan":"6.15","versionType":"semver"},{"version":"5.10.261","status":"unaffected","lessThanOrEqual":"5.10.*","versionType":"semver"},{"version":"5.15.212","status":"unaffected","lessThanOrEqual":"5.15.*","versionType":"semver"},{"version":"6.1.178","status":"unaffected","lessThanOrEqual":"6.1.*","versionType":"semver"},{"version":"6.6.145","status":"unaffected","lessThanOrEqual":"6.6.*","versionType":"semver"},{"version":"6.12.97","status":"unaffected","lessThanOrEqual":"6.12.*","versionType":"semver"},{"version":"6.18.40","status":"unaffected","lessThanOrEqual":"6.18.*","versionType":"semver"},{"version":"7.1.5","status":"unaffected","lessThanOrEqual":"7.1.*","versionType":"semver"},{"version":"7.2","status":"unaffected","lessThanOrEqual":"*","versionType":"original_commit_for_fix"}],"repo":"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git","programFiles":["net/sched/sch_fq_codel.c"]}],"references":[{"url":"https://git.kernel.org/stable/c/3e515188393e62a718ccebee651ee74514104ff6"},{"url":"https://git.kernel.org/stable/c/20dd591d8f951e1e6aca5052be8785e6181055e2"},{"url":"https://git.kernel.org/stable/c/94a5f1efdefb01f82cd228bf4e7ef1e8fc075c80"},{"url":"https://git.kernel.org/stable/c/acc08a0c7f37ebb1901144e03a7cba7d4afd9203"},{"url":"https://git.kernel.org/stable/c/7c09843fd2b44d9bf0de798683861d1aecd62a08"},{"url":"https://git.kernel.org/stable/c/0500af8630c3253f0dde879bd3a73a06bb2f2b3f"},{"url":"https://git.kernel.org/stable/c/af54df2f44d9605614bc7ed96640302a240a9a62"},{"url":"https://git.kernel.org/stable/c/097f6fc7b1ae362dd7a9444b2572162fda73b284"}],"metrics":[{"cvssV3_1":{"version":"3.1","vectorString":"CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H","baseScore":9.8,"baseSeverity":"CRITICAL"},"scenarios":[{"lang":"en","value":"AV:N - Remote senders reach the bug when packets traverse a QFQ or other qlen_notify parent with an fq_codel child: qfq_enqueue() and qfq_dequeue() call the child peek handler during __dev_queue_xmit egress scheduling, and CoDel can drop there before qlen is restored.\nAC:L - The attacker controls traffic rate, packet size, and CoDel drop behavior to force drops during peek while qlen reads zero; this is a deterministic logic bug, not a race on uncontrollable kernel state or a rare compile-time configuration.\nPR:N - On systems where an operator has already deployed a parent qdisc with an fq_codel leaf, any remote party that can send packets into the shaped class can trigger the faulty peek/drop path with no account or capabilities on the victim host.\nUI:N - Exploitation requires only attacker-generated traffic to drive peek-time CoDel drops through the installed hierarchy; no independent action by another user or administrator is needed at trigger time.\nS:U - The flaw corrupts in-kernel QFQ/fq_codel scheduler structures and memory within the same kernel security domain; it does not cross VM, container, or IOMMU authority boundaries.\nC:H - False qlen_notify prematurely deactivates QFQ aggregates while packets remain; the fix commit shows KASAN wild-memory-access on poisoned aggregate list nodes in qfq_deactivate_agg(), giving attacker-influenced reads from freed/corrupted scheduler memory.\nI:H - Corrupted aggregate/class linkage leads to invalid hlist operations and inconsistent scheduler state that can be steered with heap layout control, yielding memory corruption primitives usable for arbitrary kernel writes or control-flow hijack.\nA:H - The published oops is a general protection fault from corrupted QFQ state during qdisc teardown, and the same corruption during live packet scheduling can reliably kernel-panic or hang affected hosts."}]}],"providerMetadata":{"shortName":"Linux","orgId":"416baaa9-dc9f-4396-8d5f-8c081fb06d67","dateUpdated":"2026-08-29T06:21:30.275Z"},"cpeApplicability":[{"nodes":[{"operator":"OR","negate":false,"cpeMatch":[{"vulnerable":true,"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionStartIncluding":"5.10.241","versionEndExcluding":"5.10.261"},{"vulnerable":true,"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionStartIncluding":"5.15.190","versionEndExcluding":"5.15.212"},{"vulnerable":true,"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionStartIncluding":"6.1.135","versionEndExcluding":"6.1.178"},{"vulnerable":true,"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionStartIncluding":"6.6.88","versionEndExcluding":"6.6.145"},{"vulnerable":true,"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionStartIncluding":"6.12.24","versionEndExcluding":"6.12.97"},{"vulnerable":true,"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionStartIncluding":"6.15","versionEndExcluding":"6.18.40"},{"vulnerable":true,"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionStartIncluding":"6.15","versionEndExcluding":"7.1.5"},{"vulnerable":true,"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionStartIncluding":"6.15","versionEndExcluding":"7.2"},{"vulnerable":true,"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionStartIncluding":"5.4.297"},{"vulnerable":true,"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionStartIncluding":"6.13.12"},{"vulnerable":true,"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionStartIncluding":"6.14.3"}]}]}],"x_generator":{"engine":"bippy-1.2.0"}},"adp":[{"title":"CISA ADP Vulnrichment","metrics":[{"other":{"type":"ssvc","content":{"id":"CVE-2026-80630","role":"CISA Coordinator","options":[{"Exploitation":"none"},{"Automatable":"yes"},{"Technical Impact":"total"}],"version":"2.0.3","timestamp":"2026-10-16T19:19:03.830771Z"}}}],"providerMetadata":{"shortName":"CISA-ADP","orgId":"134c704f-9b21-4f2e-91b3-4a467353bcc0","dateUpdated":"2026-10-16T19:26:31.257Z"}}]}}}