CVE-2026-98013: net/sched: fq_pie: clamp quantum in change path
In the Linux kernel, the following vulnerability has been resolved:
net/sched: fqpie: clamp quantum in change path
fqpiechange() accepts any quantum value from userspace, including 1. With a crafted size table qdiscpktlen reaches ~2 GiB, so quantum=1 makes the deficit-refill loop spin ~2^31 times under the qdisc lock (a soft lockup / denial of service).
Add max(256U, ...) matching fqcodelchange().
Conditions to recreate the bug: CONFIGNETSCHFQPIE=y. Requires CAPNETADMIN (namespace-local via unshare -Urn suffices).
tc qdisc add dev dummy0 root fqpie tc qdisc change dev dummy0 root fqpie quantum 1 stab data 32768 sizelog 15 celllog 0
Affected Software
Remediation
Recommended actions to resolve this vulnerability, in priority order.
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Fixed in 6.6.158.1-1 - Upgrade
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debian/linuxto a version that resolves this vulnerability.Fixed in 6.1.190-1Fixed in 6.12.115-2Fixed in 7.2.12-1Fixed in 7.2.15-1 - Upgrade
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debian/linux-6.12to a version that resolves this vulnerability.Fixed in 6.12.113-1~deb12u1 - Upgrade
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ubuntu/linux-hwe-7.0to a version that resolves this vulnerability.Fixed in 7.0.0-42.42~24.04.1 - Upgrade
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ubuntu/linux-riscv-7.0to a version that resolves this vulnerability.Fixed in 7.0.0-42.42.1~24.04.1 - Upgrade
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ubuntu/linuxto a version that resolves this vulnerability.Fixed in 7.0.0-42.42 - Upgrade
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ubuntu/linux-awsto a version that resolves this vulnerability.Fixed in 7.0.0-1016.17 - Upgrade
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ubuntu/linux-gcpto a version that resolves this vulnerability.Fixed in 7.0.0-1016.18 - Upgrade
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ubuntu/linux-ibmto a version that resolves this vulnerability.Fixed in 7.0.0-1017.17 - Upgrade
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ubuntu/linux-oem-7.0to a version that resolves this vulnerability.Fixed in 7.0.0-1017.17 - Upgrade
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ubuntu/linux-oracleto a version that resolves this vulnerability.Fixed in 7.0.0-1015.16 - Upgrade
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ubuntu/linux-riscvto a version that resolves this vulnerability.Fixed in 7.0.0-42.42.1 - Configuration
Clamp the userspace-supplied quantum in fq_pie_change() using max(256U, quantum), matching fq_codel_change().
Linux net/sched fq_pie quantum minimum in fq_pie_change() = 256
Event History
Frequently Asked Questions
Who can trigger this issue?
An attacker needs CAP_NET_ADMIN. This capability can be obtained within a local user and network namespace using unshare -Urn, so the issue is relevant where unprivileged users are permitted to create such namespaces.
What configurations are affected?
The kernel must be built with CONFIG_NET_SCH_FQ_PIE=y, and an fq_pie qdisc must be configured. Exploitation uses an fq_pie change operation with quantum set to 1 and a crafted size table.
What is the operational impact of exploitation?
The deficit-refill loop can run roughly 2^31 times while holding the qdisc lock. This can cause a soft lockup and denial of service.
How can administrators mitigate the issue before applying the fix?
Restrict CAP_NET_ADMIN and, where appropriate, prevent unprivileged users from creating user and network namespaces. Avoid allowing fq_pie qdisc changes with very small quantum values, particularly quantum 1.