{"api_version":"1","generated_at":"2026-11-11T16:05:31+00:00","cve":"CVE-2024-56770","urls":{"html":"https://cve.report/CVE-2024-56770","api":"https://cve.report/api/cve/CVE-2024-56770.json","docs":"https://cve.report/api","cve_org":"https://www.cve.org/CVERecord?id=CVE-2024-56770","nvd":"https://nvd.nist.gov/vuln/detail/CVE-2024-56770"},"summary":{"title":"net/sched: netem: account for backlog updates from child qdisc","description":"In the Linux kernel, the following vulnerability has been resolved:\n\nnet/sched: netem: account for backlog updates from child qdisc\n\nIn general, 'qlen' of any classful qdisc should keep track of the\nnumber of packets that the qdisc itself and all of its children holds.\nIn case of netem, 'qlen' only accounts for the packets in its internal\ntfifo. When netem is used with a child qdisc, the child qdisc can use\n'qdisc_tree_reduce_backlog' to inform its parent, netem, about created\nor dropped SKBs. This function updates 'qlen' and the backlog statistics\nof netem, but netem does not account for changes made by a child qdisc.\n'qlen' then indicates the wrong number of packets in the tfifo.\nIf a child qdisc creates new SKBs during enqueue and informs its parent\nabout this, netem's 'qlen' value is increased. When netem dequeues the\nnewly created SKBs from the child, the 'qlen' in netem is not updated.\nIf 'qlen' reaches the configured sch->limit, the enqueue function stops\nworking, even though the tfifo is not full.\n\nReproduce the bug:\nEnsure that the sender machine has GSO enabled. Configure netem as root\nqdisc and tbf as its child on the outgoing interface of the machine\nas follows:\n$ tc qdisc add dev <oif> root handle 1: netem delay 100ms limit 100\n$ tc qdisc add dev <oif> parent 1:0 tbf rate 50Mbit burst 1542 latency 50ms\n\nSend bulk TCP traffic out via this interface, e.g., by running an iPerf3\nclient on the machine. Check the qdisc statistics:\n$ tc -s qdisc show dev <oif>\n\nStatistics after 10s of iPerf3 TCP test before the fix (note that\nnetem's backlog > limit, netem stopped accepting packets):\nqdisc netem 1: root refcnt 2 limit 1000 delay 100ms\n Sent 2767766 bytes 1848 pkt (dropped 652, overlimits 0 requeues 0)\n backlog 4294528236b 1155p requeues 0\nqdisc tbf 10: parent 1:1 rate 50Mbit burst 1537b lat 50ms\n Sent 2767766 bytes 1848 pkt (dropped 327, overlimits 7601 requeues 0)\n backlog 0b 0p requeues 0\n\nStatistics after the fix:\nqdisc netem 1: root refcnt 2 limit 1000 delay 100ms\n Sent 37766372 bytes 24974 pkt (dropped 9, overlimits 0 requeues 0)\n backlog 0b 0p requeues 0\nqdisc tbf 10: parent 1:1 rate 50Mbit burst 1537b lat 50ms\n Sent 37766372 bytes 24974 pkt (dropped 327, overlimits 96017 requeues 0)\n backlog 0b 0p requeues 0\n\ntbf segments the GSO SKBs (tbf_segment) and updates the netem's 'qlen'.\nThe interface fully stops transferring packets and \"locks\". In this case,\nthe child qdisc and tfifo are empty, but 'qlen' indicates the tfifo is at\nits limit and no more packets are accepted.\n\nThis patch adds a counter for the entries in the tfifo. Netem's 'qlen' is\nonly decreased when a packet is returned by its dequeue function, and not\nduring enqueuing into the child qdisc. External updates to 'qlen' are thus\naccounted for and only the behavior of the backlog statistics changes. As\nin other qdiscs, 'qlen' then keeps track of  how many packets are held in\nnetem and all of its children. As before, sch->limit remains as the\nmaximum number of packets in the tfifo. The same applies to netem's\nbacklog statistics.","state":"PUBLISHED","assigner":"Linux","published_at":"2025-01-08 17:15:15","updated_at":"2026-10-15 02:17:10"},"problem_types":["NVD-CWE-noinfo","CWE-noinfo Not enough 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the Linux kernel, the following vulnerability has been resolved:\n\nnet/sched: netem: account for backlog updates from child qdisc\n\nIn general, 'qlen' of any classful qdisc should keep track of the\nnumber of packets that the qdisc itself and all of its children holds.\nIn case of netem, 'qlen' only accounts for the packets in its internal\ntfifo. When netem is used with a child qdisc, the child qdisc can use\n'qdisc_tree_reduce_backlog' to inform its parent, netem, about created\nor dropped SKBs. This function updates 'qlen' and the backlog statistics\nof netem, but netem does not account for changes made by a child qdisc.\n'qlen' then indicates the wrong number of packets in the tfifo.\nIf a child qdisc creates new SKBs during enqueue and informs its parent\nabout this, netem's 'qlen' value is increased. When netem dequeues the\nnewly created SKBs from the child, the 'qlen' in netem is not updated.\nIf 'qlen' reaches the configured sch->limit, the enqueue function stops\nworking, even though the tfifo is not full.\n\nReproduce the bug:\nEnsure that the sender machine has GSO enabled. Configure netem as root\nqdisc and tbf as its child on the outgoing interface of the machine\nas follows:\n$ tc qdisc add dev <oif> root handle 1: netem delay 100ms limit 100\n$ tc qdisc add dev <oif> parent 1:0 tbf rate 50Mbit burst 1542 latency 50ms\n\nSend bulk TCP traffic out via this interface, e.g., by running an iPerf3\nclient on the machine. Check the qdisc statistics:\n$ tc -s qdisc show dev <oif>\n\nStatistics after 10s of iPerf3 TCP test before the fix (note that\nnetem's backlog > limit, netem stopped accepting packets):\nqdisc netem 1: root refcnt 2 limit 1000 delay 100ms\n Sent 2767766 bytes 1848 pkt (dropped 652, overlimits 0 requeues 0)\n backlog 4294528236b 1155p requeues 0\nqdisc tbf 10: parent 1:1 rate 50Mbit burst 1537b lat 50ms\n Sent 2767766 bytes 1848 pkt (dropped 327, overlimits 7601 requeues 0)\n backlog 0b 0p requeues 0\n\nStatistics after the fix:\nqdisc netem 1: root refcnt 2 limit 1000 delay 100ms\n Sent 37766372 bytes 24974 pkt (dropped 9, overlimits 0 requeues 0)\n backlog 0b 0p requeues 0\nqdisc tbf 10: parent 1:1 rate 50Mbit burst 1537b lat 50ms\n Sent 37766372 bytes 24974 pkt (dropped 327, overlimits 96017 requeues 0)\n backlog 0b 0p requeues 0\n\ntbf segments the GSO SKBs (tbf_segment) and updates the netem's 'qlen'.\nThe interface fully stops transferring packets and \"locks\". In this case,\nthe child qdisc and tfifo are empty, but 'qlen' indicates the tfifo is at\nits limit and no more packets are accepted.\n\nThis patch adds a counter for the entries in the tfifo. Netem's 'qlen' is\nonly decreased when a packet is returned by its dequeue function, and not\nduring enqueuing into the child qdisc. External updates to 'qlen' are thus\naccounted for and only the behavior of the backlog statistics changes. As\nin other qdiscs, 'qlen' then keeps track of  how many packets are held in\nnetem and all of its children. As before, sch->limit remains as the\nmaximum number of packets in the tfifo. The same applies to netem's\nbacklog statistics."}],"providerMetadata":{"dateUpdated":"2026-05-11T20:58:44.252Z","orgId":"416baaa9-dc9f-4396-8d5f-8c081fb06d67","shortName":"Linux"},"references":[{"url":"https://git.kernel.org/stable/c/83c6ab12f08dcc09d4c5ac86fdb89736b28f1d31"},{"url":"https://git.kernel.org/stable/c/216509dda290f6db92c816dd54b83c1df9da9e76"},{"url":"https://git.kernel.org/stable/c/c2047b0e216c8edce227d7c42f99ac2877dad0e4"},{"url":"https://git.kernel.org/stable/c/10df49cfca73dfbbdb6c4150d859f7e8926ae427"},{"url":"https://git.kernel.org/stable/c/3824c5fad18eeb7abe0c4fc966f29959552dca3e"},{"url":"https://git.kernel.org/stable/c/356078a5c55ec8d2061fcc009fb8599f5b0527f9"},{"url":"https://git.kernel.org/stable/c/f8d4bc455047cf3903cd6f85f49978987dbb3027"}],"title":"net/sched: netem: account for backlog updates from child qdisc","x_generator":{"engine":"bippy-1.2.0"}}},"cveMetadata":{"assignerOrgId":"416baaa9-dc9f-4396-8d5f-8c081fb06d67","assignerShortName":"Linux","cveId":"CVE-2024-56770","datePublished":"2025-01-08T16:36:59.315Z","dateReserved":"2024-12-29T11:26:39.763Z","dateUpdated":"2026-10-15T01:00:21.313Z","state":"PUBLISHED"},"dataType":"CVE_RECORD","dataVersion":"5.2"},"nvd":{"publishedDate":"2025-01-08 17:15:15","lastModifiedDate":"2026-10-15 02:17:10","problem_types":["NVD-CWE-noinfo","CWE-noinfo Not enough information"],"metrics":{"cvssMetricV31":[{"source":"nvd@nist.gov","type":"Primary","cvssData":{"version":"3.1","vectorString":"CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H","baseScore":5.5,"baseSeverity":"MEDIUM","attackVector":"LOCAL","attackComplexity":"LOW","privilegesRequired":"LOW","userInteraction":"NONE","scope":"UNCHANGED","confidentialityImpact":"NONE","integrityImpact":"NONE","availabilityImpact":"HIGH"},"exploitabilityScore":1.8,"impactScore":3.6},{"source":"134c704f-9b21-4f2e-91b3-4a467353bcc0","type":"Secondary","cvssData":{"version":"3.1","vectorString":"CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H","baseScore":5.5,"baseSeverity":"MEDIUM","attackVector":"LOCAL","attackComplexity":"LOW","privilegesRequired":"LOW","userInteraction":"NONE","scope":"UNCHANGED","confidentialityImpact":"NONE","integrityImpact":"NONE","availabilityImpact":"HIGH"},"exploitabilityScore":1.8,"impactScore":3.6}],"ssvcV203":[{"source":"134c704f-9b21-4f2e-91b3-4a467353bcc0","ssvcData":{"timestamp":"2025-10-01T19:56:54.954468Z","id":"CVE-2024-56770","options":[{"exploitation":"none"},{"automatable":"no"},{"technicalImpact":"partial"}],"role":"CISA Coordinator","version":"2.0.3"}}]},"configurations":[{"nodes":[{"operator":"OR","negate":false,"cpeMatch":[{"vulnerable":true,"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionStartIncluding":"3.3","versionEndExcluding":"5.4.288","matchCriteriaId":"2BBFF06A-6037-47B4-A3CF-B6B0F51D3491"},{"vulnerable":true,"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionStartIncluding":"5.5","versionEndExcluding":"5.10.232","matchCriteriaId":"0B975945-2894-4433-BA59-0988B75B4C12"},{"vulnerable":true,"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionStartIncluding":"5.11","versionEndExcluding":"5.15.175","matchCriteriaId":"7A1F3620-6900-4852-9229-C3527377EBDA"},{"vulnerable":true,"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionStartIncluding":"5.16","versionEndExcluding":"6.1.121","matchCriteriaId":"D8DA16A0-9C6E-493E-90EE-309A34901477"},{"vulnerable":true,"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionStartIncluding":"6.2","versionEndExcluding":"6.6.67","matchCriteriaId":"BF4F2CD1-2CA6-4D6B-9B0C-57C3C4D6544A"},{"vulnerable":true,"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionStartIncluding":"6.7","versionEndExcluding":"6.12.6","matchCriteriaId":"0CB1A9BB-F95E-43DD-A2FD-147912FD91E5"},{"vulnerable":true,"criteria":"cpe:2.3:o:linux:linux_kernel:6.13:rc1:*:*:*:*:*:*","matchCriteriaId":"62567B3C-6CEE-46D0-BC2E-B3717FBF7D13"},{"vulnerable":true,"criteria":"cpe:2.3:o:linux:linux_kernel:6.13:rc2:*:*:*:*:*:*","matchCriteriaId":"5A073481-106D-4B15-B4C7-FB0213B8E1D4"}]}]}]},"legacy_mitre":{"record":{"CveYear":"2024","CveId":"56770","Ordinal":"1","Title":"net/sched: netem: account for backlog updates from child qdisc","CVE":"CVE-2024-56770","Year":"2024"},"notes":[{"CveYear":"2024","CveId":"56770","Ordinal":"1","NoteData":"In the Linux kernel, the following vulnerability has been resolved:\n\nnet/sched: netem: account for backlog updates from child qdisc\n\nIn general, 'qlen' of any classful qdisc should keep track of the\nnumber of packets that the qdisc itself and all of its children holds.\nIn case of netem, 'qlen' only accounts for the packets in its internal\ntfifo. When netem is used with a child qdisc, the child qdisc can use\n'qdisc_tree_reduce_backlog' to inform its parent, netem, about created\nor dropped SKBs. This function updates 'qlen' and the backlog statistics\nof netem, but netem does not account for changes made by a child qdisc.\n'qlen' then indicates the wrong number of packets in the tfifo.\nIf a child qdisc creates new SKBs during enqueue and informs its parent\nabout this, netem's 'qlen' value is increased. When netem dequeues the\nnewly created SKBs from the child, the 'qlen' in netem is not updated.\nIf 'qlen' reaches the configured sch->limit, the enqueue function stops\nworking, even though the tfifo is not full.\n\nReproduce the bug:\nEnsure that the sender machine has GSO enabled. Configure netem as root\nqdisc and tbf as its child on the outgoing interface of the machine\nas follows:\n$ tc qdisc add dev <oif> root handle 1: netem delay 100ms limit 100\n$ tc qdisc add dev <oif> parent 1:0 tbf rate 50Mbit burst 1542 latency 50ms\n\nSend bulk TCP traffic out via this interface, e.g., by running an iPerf3\nclient on the machine. Check the qdisc statistics:\n$ tc -s qdisc show dev <oif>\n\nStatistics after 10s of iPerf3 TCP test before the fix (note that\nnetem's backlog > limit, netem stopped accepting packets):\nqdisc netem 1: root refcnt 2 limit 1000 delay 100ms\n Sent 2767766 bytes 1848 pkt (dropped 652, overlimits 0 requeues 0)\n backlog 4294528236b 1155p requeues 0\nqdisc tbf 10: parent 1:1 rate 50Mbit burst 1537b lat 50ms\n Sent 2767766 bytes 1848 pkt (dropped 327, overlimits 7601 requeues 0)\n backlog 0b 0p requeues 0\n\nStatistics after the fix:\nqdisc netem 1: root refcnt 2 limit 1000 delay 100ms\n Sent 37766372 bytes 24974 pkt (dropped 9, overlimits 0 requeues 0)\n backlog 0b 0p requeues 0\nqdisc tbf 10: parent 1:1 rate 50Mbit burst 1537b lat 50ms\n Sent 37766372 bytes 24974 pkt (dropped 327, overlimits 96017 requeues 0)\n backlog 0b 0p requeues 0\n\ntbf segments the GSO SKBs (tbf_segment) and updates the netem's 'qlen'.\nThe interface fully stops transferring packets and \"locks\". In this case,\nthe child qdisc and tfifo are empty, but 'qlen' indicates the tfifo is at\nits limit and no more packets are accepted.\n\nThis patch adds a counter for the entries in the tfifo. Netem's 'qlen' is\nonly decreased when a packet is returned by its dequeue function, and not\nduring enqueuing into the child qdisc. External updates to 'qlen' are thus\naccounted for and only the behavior of the backlog statistics changes. As\nin other qdiscs, 'qlen' then keeps track of  how many packets are held in\nnetem and all of its children. As before, sch->limit remains as the\nmaximum number of packets in the tfifo. The same applies to netem's\nbacklog statistics.","Type":"Description","Title":"net/sched: netem: account for backlog updates from child qdisc"}]}}}