{"id":"CVE-2026-90076","state":"PUBLISHED","title":"net/sched: fq: add overflow bounds to quantum and initial quantum","description":"In the Linux kernel, the following vulnerability has been resolved:\n\nnet/sched: fq: add overflow bounds to quantum and initial quantum\n\nfq_init() computes quantum = 2 * psched_mtu() and initial_quantum = 10 *\npsched_mtu() with no overflow check. A device with a huge MTU (e.g. dummy\nwith max_mtu == 0 accepting MTU 2147483634) makes psched_mtu() return\n0x80000000; the 2 * and 10 * multiplications wrap to 0 in 32-bit\narithmetic, so q->quantum == 0. Then in fq_dequeue() the credit-refill\nloop adds 0 to f->credit (which stays <= 0) and goto begin loops\nforever under the qdisc lock, creating a soft lockup.\n\nClamp psched_mtu() to [1, 1 << 20] before multiplying so the product\ncannot wrap, then cap the result at 1 << 20, matching the bound already\nenforced on TCA_FQ_QUANTUM in fq_change().\n\nConditions to recreate the bug: a device whose MTU (plus\nhard_header_len) is large enough that 2 * psched_mtu() wraps (e.g. a\ndummy device with max_mtu == 0 accepting MTU 2147483634). Requires\nCAP_NET_ADMIN in a user namespace.","publishedAt":"2026-09-17T16:05:55.517Z","updatedAt":"2026-10-30T12:34:01.376Z","severity":null,"assigner":"Linux","products":["Linux Linux"],"affected":[{"vendor":"Linux","product":"Linux","defaultStatus":"unaffected","versions":[{"version":"afe4fd062416b158a8a8538b23adc1930a9b88dc","status":"affected","lessThan":"cf398f67d9caa71af3b9fb9319058b22fe6b524e","versionType":"git"},{"version":"afe4fd062416b158a8a8538b23adc1930a9b88dc","status":"affected","lessThan":"fd63409b669f9951f1cc6b02486a5254103800d1","versionType":"git"},{"version":"afe4fd062416b158a8a8538b23adc1930a9b88dc","status":"affected","lessThan":"d16dac3925be95ad46e986d4b139c9898b6e227f","versionType":"git"},{"version":"afe4fd062416b158a8a8538b23adc1930a9b88dc","status":"affected","lessThan":"f6b3e3848a5fca63438984acd6d9eceac80814c1","versionType":"git"},{"version":"afe4fd062416b158a8a8538b23adc1930a9b88dc","status":"affected","lessThan":"e35acd56f244d94355f9ab237c2ecc8fba5e6f04","versionType":"git"},{"version":"afe4fd062416b158a8a8538b23adc1930a9b88dc","status":"affected","lessThan":"709f34f7c28dc4dd6c40343d101850f11e172312","versionType":"git"}],"repo":"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git","programFiles":["net/sched/sch_fq.c"]},{"vendor":"Linux","product":"Linux","defaultStatus":"affected","versions":[{"version":"3.12","status":"affected"},{"version":"0","status":"unaffected","lessThan":"3.12","versionType":"semver"},{"version":"6.1.191","status":"unaffected","lessThanOrEqual":"6.1.*","versionType":"semver"},{"version":"6.6.160","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.c"]}],"references":["https://git.kernel.org/stable/c/cf398f67d9caa71af3b9fb9319058b22fe6b524e","https://git.kernel.org/stable/c/fd63409b669f9951f1cc6b02486a5254103800d1","https://git.kernel.org/stable/c/d16dac3925be95ad46e986d4b139c9898b6e227f","https://git.kernel.org/stable/c/f6b3e3848a5fca63438984acd6d9eceac80814c1","https://git.kernel.org/stable/c/e35acd56f244d94355f9ab237c2ecc8fba5e6f04","https://git.kernel.org/stable/c/709f34f7c28dc4dd6c40343d101850f11e172312"],"weaknesses":[],"ingestedAt":"2026-10-30T12:52:04.348Z","source":{"repository":"CVEProject/cvelistV5","path":"cves/2026/90xxx/CVE-2026-90076.json","commit":"1f312381e38164a43607eebab851b151dd16861e","baselineCommit":"556c9d3a8cd17e218bb8e452ba7cd619a384ff47"},"raw":{"dataType":"CVE_RECORD","dataVersion":"5.2","cveMetadata":{"cveId":"CVE-2026-90076","state":"PUBLISHED","datePublished":"2026-09-17T16:05:55.517Z","dateUpdated":"2026-10-30T12:34:01.376Z","assignerShortName":"Linux","assignerOrgId":"416baaa9-dc9f-4396-8d5f-8c081fb06d67","dateReserved":"2026-09-11T19:38:34.785Z"},"containers":{"cna":{"title":"net/sched: fq: add overflow bounds to quantum and initial quantum","descriptions":[{"lang":"en","value":"In the Linux kernel, the following vulnerability has been resolved:\n\nnet/sched: fq: add overflow bounds to quantum and initial quantum\n\nfq_init() computes quantum = 2 * psched_mtu() and initial_quantum = 10 *\npsched_mtu() with no overflow check. A device with a huge MTU (e.g. dummy\nwith max_mtu == 0 accepting MTU 2147483634) makes psched_mtu() return\n0x80000000; the 2 * and 10 * multiplications wrap to 0 in 32-bit\narithmetic, so q->quantum == 0. Then in fq_dequeue() the credit-refill\nloop adds 0 to f->credit (which stays <= 0) and goto begin loops\nforever under the qdisc lock, creating a soft lockup.\n\nClamp psched_mtu() to [1, 1 << 20] before multiplying so the product\ncannot wrap, then cap the result at 1 << 20, matching the bound already\nenforced on TCA_FQ_QUANTUM in fq_change().\n\nConditions to recreate the bug: a device whose MTU (plus\nhard_header_len) is large enough that 2 * psched_mtu() wraps (e.g. a\ndummy device with max_mtu == 0 accepting MTU 2147483634). Requires\nCAP_NET_ADMIN in a user namespace."}],"affected":[{"vendor":"Linux","product":"Linux","defaultStatus":"unaffected","versions":[{"version":"afe4fd062416b158a8a8538b23adc1930a9b88dc","status":"affected","lessThan":"cf398f67d9caa71af3b9fb9319058b22fe6b524e","versionType":"git"},{"version":"afe4fd062416b158a8a8538b23adc1930a9b88dc","status":"affected","lessThan":"fd63409b669f9951f1cc6b02486a5254103800d1","versionType":"git"},{"version":"afe4fd062416b158a8a8538b23adc1930a9b88dc","status":"affected","lessThan":"d16dac3925be95ad46e986d4b139c9898b6e227f","versionType":"git"},{"version":"afe4fd062416b158a8a8538b23adc1930a9b88dc","status":"affected","lessThan":"f6b3e3848a5fca63438984acd6d9eceac80814c1","versionType":"git"},{"version":"afe4fd062416b158a8a8538b23adc1930a9b88dc","status":"affected","lessThan":"e35acd56f244d94355f9ab237c2ecc8fba5e6f04","versionType":"git"},{"version":"afe4fd062416b158a8a8538b23adc1930a9b88dc","status":"affected","lessThan":"709f34f7c28dc4dd6c40343d101850f11e172312","versionType":"git"}],"repo":"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git","programFiles":["net/sched/sch_fq.c"]},{"vendor":"Linux","product":"Linux","defaultStatus":"affected","versions":[{"version":"3.12","status":"affected"},{"version":"0","status":"unaffected","lessThan":"3.12","versionType":"semver"},{"version":"6.1.191","status":"unaffected","lessThanOrEqual":"6.1.*","versionType":"semver"},{"version":"6.6.160","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.c"]}],"references":[{"url":"https://git.kernel.org/stable/c/cf398f67d9caa71af3b9fb9319058b22fe6b524e"},{"url":"https://git.kernel.org/stable/c/fd63409b669f9951f1cc6b02486a5254103800d1"},{"url":"https://git.kernel.org/stable/c/d16dac3925be95ad46e986d4b139c9898b6e227f"},{"url":"https://git.kernel.org/stable/c/f6b3e3848a5fca63438984acd6d9eceac80814c1"},{"url":"https://git.kernel.org/stable/c/e35acd56f244d94355f9ab237c2ecc8fba5e6f04"},{"url":"https://git.kernel.org/stable/c/709f34f7c28dc4dd6c40343d101850f11e172312"}],"providerMetadata":{"shortName":"Linux","orgId":"416baaa9-dc9f-4396-8d5f-8c081fb06d67","dateUpdated":"2026-10-30T12:34:01.376Z"},"cpeApplicability":[{"nodes":[{"operator":"OR","negate":false,"cpeMatch":[{"vulnerable":true,"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionStartIncluding":"3.12","versionEndExcluding":"6.1.191"},{"vulnerable":true,"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionStartIncluding":"3.12","versionEndExcluding":"6.6.160"},{"vulnerable":true,"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionStartIncluding":"3.12","versionEndExcluding":"6.12.110"},{"vulnerable":true,"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionStartIncluding":"3.12","versionEndExcluding":"6.18.52"},{"vulnerable":true,"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionStartIncluding":"3.12","versionEndExcluding":"7.2.6"},{"vulnerable":true,"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionStartIncluding":"3.12","versionEndExcluding":"7.3"}]}]}],"x_generator":{"engine":"bippy-1.2.0"}}}}}