{"id":"CVE-2026-90075","state":"PUBLISHED","title":"net/sched: fq_codel: clamp default quantum and mtu","description":"In the Linux kernel, the following vulnerability has been resolved:\n\nnet/sched: fq_codel: clamp default quantum and mtu\n\nfq_codel_init() sets q->quantum = psched_mtu(qdisc_dev(sch)) without\nclamping. A device with a huge MTU (e.g. dummy with max_mtu == 0\naccepting MTU 2147483634) makes psched_mtu() return 0x80000000, which\noverflows the signed flow->deficit to INT_MIN in fq_codel_dequeue(),\ncausing an infinite loop and soft lockup. Emulate fq_codel_change()\nand constrain to [256, FQ_CODEL_QUANTUM_MAX].\n\nThe same unclamped psched_mtu() is assigned to q->cparams.mtu a bit\nbelow, and fq_codel_change() never updates it. codel_should_drop()\ntests \"*backlog <= params->mtu\"; with mtu == 0x80000000 (~2 GiB) and\nthe default 32 MiB memory_limit, the test is always true, so CoDel is\nsilently and completely disabled (no drops, no ECN). Declare a single\nclamped mtu and assign both q->quantum and q->cparams.mtu from it,\nwhich also removes the double psched_mtu() call.\n\nConditions to recreate the bug: a device whose MTU (plus\nhard_header_len) wraps psched_mtu() into the sign bit (e.g. a dummy\ndevice with max_mtu == 0 accepting MTU 2147483634). Requires\nCAP_NET_ADMIN in a user namespace.","publishedAt":"2026-09-17T16:05:54.851Z","updatedAt":"2026-10-19T08:57:32.110Z","severity":null,"assigner":"Linux","products":["Linux Linux"],"affected":[{"vendor":"Linux","product":"Linux","defaultStatus":"unaffected","versions":[{"version":"4b549a2ef4bef9965d97cbd992ba67930cd3e0fe","status":"affected","lessThan":"d315ee8a07fd1810880227319cf60e6cd925ef22","versionType":"git"},{"version":"4b549a2ef4bef9965d97cbd992ba67930cd3e0fe","status":"affected","lessThan":"a9a5b2943a00df2ab81a2209f31dd9e87016f120","versionType":"git"},{"version":"4b549a2ef4bef9965d97cbd992ba67930cd3e0fe","status":"affected","lessThan":"3782067ec0d485628b6f1f9ede3eeeb4f611fcf2","versionType":"git"},{"version":"4b549a2ef4bef9965d97cbd992ba67930cd3e0fe","status":"affected","lessThan":"397e2b1f71d9f15b8b4e47d24eb620e4dff8878d","versionType":"git"},{"version":"4b549a2ef4bef9965d97cbd992ba67930cd3e0fe","status":"affected","lessThan":"324f86806673ae4a55f66d28db84577f46f615e1","versionType":"git"},{"version":"4b549a2ef4bef9965d97cbd992ba67930cd3e0fe","status":"affected","lessThan":"dfb4b61db886917244284b18b44b23d2254b82c2","versionType":"git"},{"version":"4b549a2ef4bef9965d97cbd992ba67930cd3e0fe","status":"affected","lessThan":"9f499e5827fdb6d7fdb46a7ce731852f6b1a1bb9","versionType":"git"},{"version":"4b549a2ef4bef9965d97cbd992ba67930cd3e0fe","status":"affected","lessThan":"d9ebd8f9aa8b2773235889cb903fafd61f2d8585","versionType":"git"}],"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":"3.5","status":"affected"},{"version":"0","status":"unaffected","lessThan":"3.5","versionType":"semver"},{"version":"5.10.270","status":"unaffected","lessThanOrEqual":"5.10.*","versionType":"semver"},{"version":"5.15.221","status":"unaffected","lessThanOrEqual":"5.15.*","versionType":"semver"},{"version":"6.1.188","status":"unaffected","lessThanOrEqual":"6.1.*","versionType":"semver"},{"version":"6.6.157","status":"unaffected","lessThanOrEqual":"6.6.*","versionType":"semver"},{"version":"6.12.110","status":"unaffected","lessThanOrEqual":"6.12.*","versionType":"semver"},{"version":"6.18.52","status":"unaffected","lessThanOrEqual":"6.18.*","versionType":"semver"},{"version":"7.2.6","status":"unaffected","lessThanOrEqual":"7.2.*","versionType":"semver"},{"version":"7.3","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/d315ee8a07fd1810880227319cf60e6cd925ef22","https://git.kernel.org/stable/c/a9a5b2943a00df2ab81a2209f31dd9e87016f120","https://git.kernel.org/stable/c/3782067ec0d485628b6f1f9ede3eeeb4f611fcf2","https://git.kernel.org/stable/c/397e2b1f71d9f15b8b4e47d24eb620e4dff8878d","https://git.kernel.org/stable/c/324f86806673ae4a55f66d28db84577f46f615e1","https://git.kernel.org/stable/c/dfb4b61db886917244284b18b44b23d2254b82c2","https://git.kernel.org/stable/c/9f499e5827fdb6d7fdb46a7ce731852f6b1a1bb9","https://git.kernel.org/stable/c/d9ebd8f9aa8b2773235889cb903fafd61f2d8585"],"weaknesses":[],"ingestedAt":"2026-10-29T20:13:34.582Z","source":{"repository":"CVEProject/cvelistV5","path":"cves/2026/90xxx/CVE-2026-90075.json","commit":"556c9d3a8cd17e218bb8e452ba7cd619a384ff47"},"raw":{"dataType":"CVE_RECORD","dataVersion":"5.2","cveMetadata":{"cveId":"CVE-2026-90075","state":"PUBLISHED","datePublished":"2026-09-17T16:05:54.851Z","dateUpdated":"2026-10-19T08:57:32.110Z","assignerShortName":"Linux","assignerOrgId":"416baaa9-dc9f-4396-8d5f-8c081fb06d67","dateReserved":"2026-09-11T19:38:34.785Z"},"containers":{"cna":{"title":"net/sched: fq_codel: clamp default quantum and mtu","descriptions":[{"lang":"en","value":"In the Linux kernel, the following vulnerability has been resolved:\n\nnet/sched: fq_codel: clamp default quantum and mtu\n\nfq_codel_init() sets q->quantum = psched_mtu(qdisc_dev(sch)) without\nclamping. A device with a huge MTU (e.g. dummy with max_mtu == 0\naccepting MTU 2147483634) makes psched_mtu() return 0x80000000, which\noverflows the signed flow->deficit to INT_MIN in fq_codel_dequeue(),\ncausing an infinite loop and soft lockup. Emulate fq_codel_change()\nand constrain to [256, FQ_CODEL_QUANTUM_MAX].\n\nThe same unclamped psched_mtu() is assigned to q->cparams.mtu a bit\nbelow, and fq_codel_change() never updates it. codel_should_drop()\ntests \"*backlog <= params->mtu\"; with mtu == 0x80000000 (~2 GiB) and\nthe default 32 MiB memory_limit, the test is always true, so CoDel is\nsilently and completely disabled (no drops, no ECN). Declare a single\nclamped mtu and assign both q->quantum and q->cparams.mtu from it,\nwhich also removes the double psched_mtu() call.\n\nConditions to recreate the bug: a device whose MTU (plus\nhard_header_len) wraps psched_mtu() into the sign bit (e.g. a dummy\ndevice with max_mtu == 0 accepting MTU 2147483634). Requires\nCAP_NET_ADMIN in a user namespace."}],"affected":[{"vendor":"Linux","product":"Linux","defaultStatus":"unaffected","versions":[{"version":"4b549a2ef4bef9965d97cbd992ba67930cd3e0fe","status":"affected","lessThan":"d315ee8a07fd1810880227319cf60e6cd925ef22","versionType":"git"},{"version":"4b549a2ef4bef9965d97cbd992ba67930cd3e0fe","status":"affected","lessThan":"a9a5b2943a00df2ab81a2209f31dd9e87016f120","versionType":"git"},{"version":"4b549a2ef4bef9965d97cbd992ba67930cd3e0fe","status":"affected","lessThan":"3782067ec0d485628b6f1f9ede3eeeb4f611fcf2","versionType":"git"},{"version":"4b549a2ef4bef9965d97cbd992ba67930cd3e0fe","status":"affected","lessThan":"397e2b1f71d9f15b8b4e47d24eb620e4dff8878d","versionType":"git"},{"version":"4b549a2ef4bef9965d97cbd992ba67930cd3e0fe","status":"affected","lessThan":"324f86806673ae4a55f66d28db84577f46f615e1","versionType":"git"},{"version":"4b549a2ef4bef9965d97cbd992ba67930cd3e0fe","status":"affected","lessThan":"dfb4b61db886917244284b18b44b23d2254b82c2","versionType":"git"},{"version":"4b549a2ef4bef9965d97cbd992ba67930cd3e0fe","status":"affected","lessThan":"9f499e5827fdb6d7fdb46a7ce731852f6b1a1bb9","versionType":"git"},{"version":"4b549a2ef4bef9965d97cbd992ba67930cd3e0fe","status":"affected","lessThan":"d9ebd8f9aa8b2773235889cb903fafd61f2d8585","versionType":"git"}],"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":"3.5","status":"affected"},{"version":"0","status":"unaffected","lessThan":"3.5","versionType":"semver"},{"version":"5.10.270","status":"unaffected","lessThanOrEqual":"5.10.*","versionType":"semver"},{"version":"5.15.221","status":"unaffected","lessThanOrEqual":"5.15.*","versionType":"semver"},{"version":"6.1.188","status":"unaffected","lessThanOrEqual":"6.1.*","versionType":"semver"},{"version":"6.6.157","status":"unaffected","lessThanOrEqual":"6.6.*","versionType":"semver"},{"version":"6.12.110","status":"unaffected","lessThanOrEqual":"6.12.*","versionType":"semver"},{"version":"6.18.52","status":"unaffected","lessThanOrEqual":"6.18.*","versionType":"semver"},{"version":"7.2.6","status":"unaffected","lessThanOrEqual":"7.2.*","versionType":"semver"},{"version":"7.3","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/d315ee8a07fd1810880227319cf60e6cd925ef22"},{"url":"https://git.kernel.org/stable/c/a9a5b2943a00df2ab81a2209f31dd9e87016f120"},{"url":"https://git.kernel.org/stable/c/3782067ec0d485628b6f1f9ede3eeeb4f611fcf2"},{"url":"https://git.kernel.org/stable/c/397e2b1f71d9f15b8b4e47d24eb620e4dff8878d"},{"url":"https://git.kernel.org/stable/c/324f86806673ae4a55f66d28db84577f46f615e1"},{"url":"https://git.kernel.org/stable/c/dfb4b61db886917244284b18b44b23d2254b82c2"},{"url":"https://git.kernel.org/stable/c/9f499e5827fdb6d7fdb46a7ce731852f6b1a1bb9"},{"url":"https://git.kernel.org/stable/c/d9ebd8f9aa8b2773235889cb903fafd61f2d8585"}],"providerMetadata":{"shortName":"Linux","orgId":"416baaa9-dc9f-4396-8d5f-8c081fb06d67","dateUpdated":"2026-10-19T08:57:32.110Z"},"cpeApplicability":[{"nodes":[{"operator":"OR","negate":false,"cpeMatch":[{"vulnerable":true,"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionStartIncluding":"3.5","versionEndExcluding":"5.10.270"},{"vulnerable":true,"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionStartIncluding":"3.5","versionEndExcluding":"5.15.221"},{"vulnerable":true,"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionStartIncluding":"3.5","versionEndExcluding":"6.1.188"},{"vulnerable":true,"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionStartIncluding":"3.5","versionEndExcluding":"6.6.157"},{"vulnerable":true,"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionStartIncluding":"3.5","versionEndExcluding":"6.12.110"},{"vulnerable":true,"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionStartIncluding":"3.5","versionEndExcluding":"6.18.52"},{"vulnerable":true,"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionStartIncluding":"3.5","versionEndExcluding":"7.2.6"},{"vulnerable":true,"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionStartIncluding":"3.5","versionEndExcluding":"7.3"}]}]}],"x_generator":{"engine":"bippy-1.2.0"}}}}}