net/sched: fq_codel: clamp default quantum and mtu

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Summary

CVECVE-2026-90075
StatePUBLISHED
AssignerLinux
Source PriorityCVE Program / NVD first with legacy fallback
Published2026-09-17 17:16:56 UTC
Updated2026-09-17 17:16:56 UTC
DescriptionIn the Linux kernel, the following vulnerability has been resolved: net/sched: fq_codel: clamp default quantum and mtu fq_codel_init() sets q->quantum = psched_mtu(qdisc_dev(sch)) without clamping. A device with a huge MTU (e.g. dummy with max_mtu == 0 accepting MTU 2147483634) makes psched_mtu() return 0x80000000, which overflows the signed flow->deficit to INT_MIN in fq_codel_dequeue(), causing an infinite loop and soft lockup. Emulate fq_codel_change() and constrain to [256, FQ_CODEL_QUANTUM_MAX]. The same unclamped psched_mtu() is assigned to q->cparams.mtu a bit below, and fq_codel_change() never updates it. codel_should_drop() tests "*backlog <= params->mtu"; with mtu == 0x80000000 (~2 GiB) and the default 32 MiB memory_limit, the test is always true, so CoDel is silently and completely disabled (no drops, no ECN). Declare a single clamped mtu and assign both q->quantum and q->cparams.mtu from it, which also removes the double psched_mtu() call. Conditions to recreate the bug: a device whose MTU (plus hard_header_len) wraps psched_mtu() into the sign bit (e.g. a dummy device with max_mtu == 0 accepting MTU 2147483634). Requires CAP_NET_ADMIN in a user namespace.

Vendor Declared Affected Products

SourceVendorProductVersionPlatforms
CNA Linux Linux affected 4b549a2ef4bef9965d97cbd992ba67930cd3e0fe d315ee8a07fd1810880227319cf60e6cd925ef22 git Not specified
CNA Linux Linux affected 4b549a2ef4bef9965d97cbd992ba67930cd3e0fe a9a5b2943a00df2ab81a2209f31dd9e87016f120 git Not specified
CNA Linux Linux affected 4b549a2ef4bef9965d97cbd992ba67930cd3e0fe 3782067ec0d485628b6f1f9ede3eeeb4f611fcf2 git Not specified
CNA Linux Linux affected 4b549a2ef4bef9965d97cbd992ba67930cd3e0fe 397e2b1f71d9f15b8b4e47d24eb620e4dff8878d git Not specified
CNA Linux Linux affected 4b549a2ef4bef9965d97cbd992ba67930cd3e0fe 324f86806673ae4a55f66d28db84577f46f615e1 git Not specified
CNA Linux Linux affected 4b549a2ef4bef9965d97cbd992ba67930cd3e0fe dfb4b61db886917244284b18b44b23d2254b82c2 git Not specified
CNA Linux Linux affected 4b549a2ef4bef9965d97cbd992ba67930cd3e0fe 9f499e5827fdb6d7fdb46a7ce731852f6b1a1bb9 git Not specified
CNA Linux Linux affected 4b549a2ef4bef9965d97cbd992ba67930cd3e0fe d9ebd8f9aa8b2773235889cb903fafd61f2d8585 git Not specified
CNA Linux Linux affected 3.5 Not specified
CNA Linux Linux unaffected 3.5 semver Not specified
CNA Linux Linux unaffected 5.10.270 5.10.* semver Not specified
CNA Linux Linux unaffected 5.15.221 5.15.* semver Not specified
CNA Linux Linux unaffected 6.1.188 6.1.* semver Not specified
CNA Linux Linux unaffected 6.6.157 6.6.* semver Not specified
CNA Linux Linux unaffected 6.12.110 6.12.* semver Not specified
CNA Linux Linux unaffected 6.18.52 6.18.* semver Not specified
CNA Linux Linux unaffected 7.2.6 7.2.* semver Not specified
CNA Linux Linux unaffected 7.3-rc1 * original_commit_for_fix Not specified

References

ReferenceSourceLinkTags
git.kernel.org/stable/c/397e2b1f71d9f15b8b4e47d24eb620e4dff8878d 416baaa9-dc9f-4396-8d5f-8c081fb06d67 git.kernel.org
git.kernel.org/stable/c/9f499e5827fdb6d7fdb46a7ce731852f6b1a1bb9 416baaa9-dc9f-4396-8d5f-8c081fb06d67 git.kernel.org
git.kernel.org/stable/c/324f86806673ae4a55f66d28db84577f46f615e1 416baaa9-dc9f-4396-8d5f-8c081fb06d67 git.kernel.org
git.kernel.org/stable/c/a9a5b2943a00df2ab81a2209f31dd9e87016f120 416baaa9-dc9f-4396-8d5f-8c081fb06d67 git.kernel.org
git.kernel.org/stable/c/dfb4b61db886917244284b18b44b23d2254b82c2 416baaa9-dc9f-4396-8d5f-8c081fb06d67 git.kernel.org
git.kernel.org/stable/c/3782067ec0d485628b6f1f9ede3eeeb4f611fcf2 416baaa9-dc9f-4396-8d5f-8c081fb06d67 git.kernel.org
git.kernel.org/stable/c/d315ee8a07fd1810880227319cf60e6cd925ef22 416baaa9-dc9f-4396-8d5f-8c081fb06d67 git.kernel.org
git.kernel.org/stable/c/d9ebd8f9aa8b2773235889cb903fafd61f2d8585 416baaa9-dc9f-4396-8d5f-8c081fb06d67 git.kernel.org
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