CVE-2024-56770 (GCVE-0-2024-56770)
Vulnerability from cvelistv5 – Published: 2025-01-08 16:36 – Updated: 2026-10-15 01:00
VLAI
EPSS
VEX
Title
net/sched: netem: account for backlog updates from child qdisc
Summary
In the Linux kernel, the following vulnerability has been resolved:
net/sched: netem: account for backlog updates from child qdisc
In general, 'qlen' of any classful qdisc should keep track of the
number of packets that the qdisc itself and all of its children holds.
In case of netem, 'qlen' only accounts for the packets in its internal
tfifo. When netem is used with a child qdisc, the child qdisc can use
'qdisc_tree_reduce_backlog' to inform its parent, netem, about created
or dropped SKBs. This function updates 'qlen' and the backlog statistics
of netem, but netem does not account for changes made by a child qdisc.
'qlen' then indicates the wrong number of packets in the tfifo.
If a child qdisc creates new SKBs during enqueue and informs its parent
about this, netem's 'qlen' value is increased. When netem dequeues the
newly created SKBs from the child, the 'qlen' in netem is not updated.
If 'qlen' reaches the configured sch->limit, the enqueue function stops
working, even though the tfifo is not full.
Reproduce the bug:
Ensure that the sender machine has GSO enabled. Configure netem as root
qdisc and tbf as its child on the outgoing interface of the machine
as follows:
$ tc qdisc add dev <oif> root handle 1: netem delay 100ms limit 100
$ tc qdisc add dev <oif> parent 1:0 tbf rate 50Mbit burst 1542 latency 50ms
Send bulk TCP traffic out via this interface, e.g., by running an iPerf3
client on the machine. Check the qdisc statistics:
$ tc -s qdisc show dev <oif>
Statistics after 10s of iPerf3 TCP test before the fix (note that
netem's backlog > limit, netem stopped accepting packets):
qdisc netem 1: root refcnt 2 limit 1000 delay 100ms
Sent 2767766 bytes 1848 pkt (dropped 652, overlimits 0 requeues 0)
backlog 4294528236b 1155p requeues 0
qdisc tbf 10: parent 1:1 rate 50Mbit burst 1537b lat 50ms
Sent 2767766 bytes 1848 pkt (dropped 327, overlimits 7601 requeues 0)
backlog 0b 0p requeues 0
Statistics after the fix:
qdisc netem 1: root refcnt 2 limit 1000 delay 100ms
Sent 37766372 bytes 24974 pkt (dropped 9, overlimits 0 requeues 0)
backlog 0b 0p requeues 0
qdisc tbf 10: parent 1:1 rate 50Mbit burst 1537b lat 50ms
Sent 37766372 bytes 24974 pkt (dropped 327, overlimits 96017 requeues 0)
backlog 0b 0p requeues 0
tbf segments the GSO SKBs (tbf_segment) and updates the netem's 'qlen'.
The interface fully stops transferring packets and "locks". In this case,
the child qdisc and tfifo are empty, but 'qlen' indicates the tfifo is at
its limit and no more packets are accepted.
This patch adds a counter for the entries in the tfifo. Netem's 'qlen' is
only decreased when a packet is returned by its dequeue function, and not
during enqueuing into the child qdisc. External updates to 'qlen' are thus
accounted for and only the behavior of the backlog statistics changes. As
in other qdiscs, 'qlen' then keeps track of how many packets are held in
netem and all of its children. As before, sch->limit remains as the
maximum number of packets in the tfifo. The same applies to netem's
backlog statistics.
Severity
5.5 (Medium)
SSVC
Exploitation: none
Automatable: no
Technical Impact: partial
CISA Coordinator · CISA-ADP (v2.0.3)
Decision recorded 2025-10-01 19:56 UTC
Assigner
References
11 references
Impacted products
8 products
| Vendor | Product | Version | CPE status | |
|---|---|---|---|---|
| Linux | Linux |
Affected:
50612537e9ab29693122fab20fc1eed235054ffe , < 83c6ab12f08dcc09d4c5ac86fdb89736b28f1d31
(git)
Affected: 50612537e9ab29693122fab20fc1eed235054ffe , < 216509dda290f6db92c816dd54b83c1df9da9e76 (git) Affected: 50612537e9ab29693122fab20fc1eed235054ffe , < c2047b0e216c8edce227d7c42f99ac2877dad0e4 (git) Affected: 50612537e9ab29693122fab20fc1eed235054ffe , < 10df49cfca73dfbbdb6c4150d859f7e8926ae427 (git) Affected: 50612537e9ab29693122fab20fc1eed235054ffe , < 3824c5fad18eeb7abe0c4fc966f29959552dca3e (git) Affected: 50612537e9ab29693122fab20fc1eed235054ffe , < 356078a5c55ec8d2061fcc009fb8599f5b0527f9 (git) Affected: 50612537e9ab29693122fab20fc1eed235054ffe , < f8d4bc455047cf3903cd6f85f49978987dbb3027 (git) |
guessed | |
| Linux | Linux |
Affected:
3.3
Unaffected: 0 , < 3.3 (semver) Unaffected: 5.4.288 , ≤ 5.4.* (semver) Unaffected: 5.10.232 , ≤ 5.10.* (semver) Unaffected: 5.15.175 , ≤ 5.15.* (semver) Unaffected: 6.1.121 , ≤ 6.1.* (semver) Unaffected: 6.6.67 , ≤ 6.6.* (semver) Unaffected: 6.12.6 , ≤ 6.12.* (semver) Unaffected: 6.13 , ≤ * (original_commit_for_fix) |
guessed | |
| Siemens | SIMATIC S7-1500 CPU 1518-4 PN/DP MFP |
Affected:
V3.1.0 , < V3.1.5
(custom)
|
guessed | |
| Siemens | SIMATIC S7-1500 CPU 1518F-4 PN/DP MFP |
Affected:
V3.1.0 , < V3.1.5
(custom)
|
guessed | |
| Siemens | SIPLUS S7-1500 CPU 1518-4 PN/DP MFP |
Affected:
V3.1.0 , < V3.1.5
(custom)
|
guessed | |
| Siemens | RUGGEDCOM RST2428P |
Affected:
0 , < V3.2
(custom)
|
guessed | |
| Siemens | SCALANCE XC-300/XR-300/XC-400/XR-500WG/XR-500 family |
Affected:
0 , < V3.2
(custom)
|
guessed | |
| Siemens | SCALANCE XCM-/XRM-/XCH-/XRH-300 family |
Affected:
0 , < V3.2
(custom)
|
guessed |
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"value": "In the Linux kernel, the following vulnerability has been resolved:\n\nnet/sched: netem: account for backlog updates from child qdisc\n\nIn general, \u0027qlen\u0027 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, \u0027qlen\u0027 only accounts for the packets in its internal\ntfifo. When netem is used with a child qdisc, the child qdisc can use\n\u0027qdisc_tree_reduce_backlog\u0027 to inform its parent, netem, about created\nor dropped SKBs. This function updates \u0027qlen\u0027 and the backlog statistics\nof netem, but netem does not account for changes made by a child qdisc.\n\u0027qlen\u0027 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\u0027s \u0027qlen\u0027 value is increased. When netem dequeues the\nnewly created SKBs from the child, the \u0027qlen\u0027 in netem is not updated.\nIf \u0027qlen\u0027 reaches the configured sch-\u003elimit, 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 \u003coif\u003e root handle 1: netem delay 100ms limit 100\n$ tc qdisc add dev \u003coif\u003e 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 \u003coif\u003e\n\nStatistics after 10s of iPerf3 TCP test before the fix (note that\nnetem\u0027s backlog \u003e 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\u0027s \u0027qlen\u0027.\nThe interface fully stops transferring packets and \"locks\". In this case,\nthe child qdisc and tfifo are empty, but \u0027qlen\u0027 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\u0027s \u0027qlen\u0027 is\nonly decreased when a packet is returned by its dequeue function, and not\nduring enqueuing into the child qdisc. External updates to \u0027qlen\u0027 are thus\naccounted for and only the behavior of the backlog statistics changes. As\nin other qdiscs, \u0027qlen\u0027 then keeps track of how many packets are held in\nnetem and all of its children. As before, sch-\u003elimit remains as the\nmaximum number of packets in the tfifo. The same applies to netem\u0027s\nbacklog statistics."
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"value": "In the Linux kernel, the following vulnerability has been resolved:\n\nnet/sched: netem: account for backlog updates from child qdisc\n\nIn general, \u0027qlen\u0027 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, \u0027qlen\u0027 only accounts for the packets in its internal\ntfifo. When netem is used with a child qdisc, the child qdisc can use\n\u0027qdisc_tree_reduce_backlog\u0027 to inform its parent, netem, about created\nor dropped SKBs. This function updates \u0027qlen\u0027 and the backlog statistics\nof netem, but netem does not account for changes made by a child qdisc.\n\u0027qlen\u0027 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\u0027s \u0027qlen\u0027 value is increased. When netem dequeues the\nnewly created SKBs from the child, the \u0027qlen\u0027 in netem is not updated.\nIf \u0027qlen\u0027 reaches the configured sch-\u003elimit, 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 \u003coif\u003e root handle 1: netem delay 100ms limit 100\n$ tc qdisc add dev \u003coif\u003e 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 \u003coif\u003e\n\nStatistics after 10s of iPerf3 TCP test before the fix (note that\nnetem\u0027s backlog \u003e 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\u0027s \u0027qlen\u0027.\nThe interface fully stops transferring packets and \"locks\". In this case,\nthe child qdisc and tfifo are empty, but \u0027qlen\u0027 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\u0027s \u0027qlen\u0027 is\nonly decreased when a packet is returned by its dequeue function, and not\nduring enqueuing into the child qdisc. External updates to \u0027qlen\u0027 are thus\naccounted for and only the behavior of the backlog statistics changes. As\nin other qdiscs, \u0027qlen\u0027 then keeps track of how many packets are held in\nnetem and all of its children. As before, sch-\u003elimit remains as the\nmaximum number of packets in the tfifo. The same applies to netem\u0027s\nbacklog statistics."
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"value": "En el kernel de Linux, se ha resuelto la siguiente vulnerabilidad: net/sched: netem: contabilizar las actualizaciones atrasadas de la qdisc secundaria En general, \u0027qlen\u0027 de cualquier qdisc con clase debe realizar un seguimiento de la cantidad de paquetes que la propia qdisc y todos sus hijos contienen. En el caso de netem, \u0027qlen\u0027 solo contabiliza los paquetes en su tfifo interno. Cuando netem se usa con una qdisc secundaria, la qdisc secundaria puede usar \u0027qdisc_tree_reduce_backlog\u0027 para informar a su padre, netem, sobre los SKB creados o descartados. Esta funci\u00f3n actualiza \u0027qlen\u0027 y las estad\u00edsticas de atraso de netem, pero netem no contabiliza los cambios realizados por una qdisc secundaria. \u0027qlen\u0027 luego indica la cantidad incorrecta de paquetes en el tfifo. Si una qdisc secundaria crea nuevos SKB durante la puesta en cola e informa a su padre sobre esto, el valor \u0027qlen\u0027 de netem aumenta. Cuando netem saca de la cola los SKB reci\u00e9n creados del hijo, el \u0027qlen\u0027 en netem no se actualiza. Si \u0027qlen\u0027 alcanza el sch-\u0026gt;limit configurado, la funci\u00f3n de puesta en cola deja de funcionar, aunque el tfifo no est\u00e9 lleno. Reproducir el error: Aseg\u00farese de que la m\u00e1quina remitente tenga GSO habilitado. Configure netem como qdisc ra\u00edz y tbf como su hijo en la interfaz de salida de la m\u00e1quina de la siguiente manera: $ tc qdisc add dev root handle 1: netem delay 100ms limit 100 $ tc qdisc add dev parent 1:0 tbf rate 50Mbit burst 1542 latency 50ms Env\u00ede tr\u00e1fico TCP masivo a trav\u00e9s de esta interfaz, por ejemplo, ejecutando un cliente iPerf3 en la m\u00e1quina. Compruebe las estad\u00edsticas de qdisc: $ tc -s qdisc show dev Estad\u00edsticas despu\u00e9s de 10 s de prueba TCP de iPerf3 antes de la correcci\u00f3n (tenga en cuenta que el backlog de netem \u0026gt; limit, netem dej\u00f3 de aceptar paquetes): qdisc netem 1: root refcnt 2 limit 1000 delay 100ms Sent 2767766 bytes 1848 pkt (dropped 652, overlimits 0 requeues 0) backlog 4294528236b 1155p requeues 0 qdisc tbf 10: parent 1:1 rate 50Mbit burst 1537b lat 50ms Sent 2767766 bytes 1848 pkt (dropped 327, overlimits 7601 requeues 0) backlog 0b 0p requeues 0 Estad\u00edsticas despu\u00e9s de la correcci\u00f3n: qdisc netem 1: root refcnt 2 limit 1000 delay 100ms Enviados 37766372 bytes 24974 pkt (derramados 9, sobrepasa los l\u00edmites 0, pone en cola 0) backlog 0b 0p pone en cola 0 qdisc tbf 10: padre 1:1 tasa 50Mbit r\u00e1faga 1537b lat 50ms Enviados 37766372 bytes 24974 pkt (derramados 327, sobrepasa los l\u00edmites 96017, pone en cola 0) backlog 0b 0p pone en cola 0 tbf segmenta los SKB de GSO (tbf_segment) y actualiza el \u0027qlen\u0027 de netem. La interfaz deja de transferir paquetes por completo y se \"bloquea\". En este caso, la qdisc secundaria y la tfifo est\u00e1n vac\u00edas, pero \u0027qlen\u0027 indica que la tfifo est\u00e1 en su l\u00edmite y no se aceptan m\u00e1s paquetes. Este parche agrega un contador para las entradas en la tfifo. La \u0027qlen\u0027 de Netem solo se reduce cuando la funci\u00f3n de desencolado devuelve un paquete, y no durante la puesta en cola en la qdisc secundaria. De este modo, se tienen en cuenta las actualizaciones externas de \u0027qlen\u0027 y solo cambia el comportamiento de las estad\u00edsticas de la lista de espera. Como en otras qdisc, \u0027qlen\u0027 realiza un seguimiento de cu\u00e1ntos paquetes se mantienen en netem y en todas sus hijas. Como antes, sch-\u0026gt;limit permanece como el n\u00famero m\u00e1ximo de paquetes en la tfifo. Lo mismo se aplica a las estad\u00edsticas de la lista de espera de netem."
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"baseScore": 5.5,
"baseSeverity": "MEDIUM",
"confidentialityImpact": "NONE",
"integrityImpact": "NONE",
"privilegesRequired": "LOW",
"scope": "UNCHANGED",
"userInteraction": "NONE",
"vectorString": "CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H",
"version": "3.1"
}
},
{
"other": {
"content": {
"id": "CVE-2024-56770",
"options": [
{
"Exploitation": "none"
},
{
"Automatable": "no"
},
{
"Technical Impact": "partial"
}
],
"role": "CISA Coordinator",
"timestamp": "2025-10-01T19:56:54.954468Z",
"version": "2.0.3"
},
"type": "ssvc"
}
}
],
"problemTypes": [
{
"descriptions": [
{
"description": "CWE-noinfo Not enough information",
"lang": "en",
"type": "CWE"
}
]
}
],
"providerMetadata": {
"dateUpdated": "2025-10-01T15:50:27.416Z",
"orgId": "134c704f-9b21-4f2e-91b3-4a467353bcc0",
"shortName": "CISA-ADP"
},
"title": "CISA ADP Vulnrichment"
}
],
"cna": {
"affected": [
{
"defaultStatus": "unaffected",
"product": "Linux",
"programFiles": [
"net/sched/sch_netem.c"
],
"repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git",
"vendor": "Linux",
"versions": [
{
"lessThan": "83c6ab12f08dcc09d4c5ac86fdb89736b28f1d31",
"status": "affected",
"version": "50612537e9ab29693122fab20fc1eed235054ffe",
"versionType": "git"
},
{
"lessThan": "216509dda290f6db92c816dd54b83c1df9da9e76",
"status": "affected",
"version": "50612537e9ab29693122fab20fc1eed235054ffe",
"versionType": "git"
},
{
"lessThan": "c2047b0e216c8edce227d7c42f99ac2877dad0e4",
"status": "affected",
"version": "50612537e9ab29693122fab20fc1eed235054ffe",
"versionType": "git"
},
{
"lessThan": "10df49cfca73dfbbdb6c4150d859f7e8926ae427",
"status": "affected",
"version": "50612537e9ab29693122fab20fc1eed235054ffe",
"versionType": "git"
},
{
"lessThan": "3824c5fad18eeb7abe0c4fc966f29959552dca3e",
"status": "affected",
"version": "50612537e9ab29693122fab20fc1eed235054ffe",
"versionType": "git"
},
{
"lessThan": "356078a5c55ec8d2061fcc009fb8599f5b0527f9",
"status": "affected",
"version": "50612537e9ab29693122fab20fc1eed235054ffe",
"versionType": "git"
},
{
"lessThan": "f8d4bc455047cf3903cd6f85f49978987dbb3027",
"status": "affected",
"version": "50612537e9ab29693122fab20fc1eed235054ffe",
"versionType": "git"
}
]
},
{
"defaultStatus": "affected",
"product": "Linux",
"programFiles": [
"net/sched/sch_netem.c"
],
"repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git",
"vendor": "Linux",
"versions": [
{
"status": "affected",
"version": "3.3"
},
{
"lessThan": "3.3",
"status": "unaffected",
"version": "0",
"versionType": "semver"
},
{
"lessThanOrEqual": "5.4.*",
"status": "unaffected",
"version": "5.4.288",
"versionType": "semver"
},
{
"lessThanOrEqual": "5.10.*",
"status": "unaffected",
"version": "5.10.232",
"versionType": "semver"
},
{
"lessThanOrEqual": "5.15.*",
"status": "unaffected",
"version": "5.15.175",
"versionType": "semver"
},
{
"lessThanOrEqual": "6.1.*",
"status": "unaffected",
"version": "6.1.121",
"versionType": "semver"
},
{
"lessThanOrEqual": "6.6.*",
"status": "unaffected",
"version": "6.6.67",
"versionType": "semver"
},
{
"lessThanOrEqual": "6.12.*",
"status": "unaffected",
"version": "6.12.6",
"versionType": "semver"
},
{
"lessThanOrEqual": "*",
"status": "unaffected",
"version": "6.13",
"versionType": "original_commit_for_fix"
}
]
}
],
"cpeApplicability": [
{
"nodes": [
{
"cpeMatch": [
{
"criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*",
"versionEndExcluding": "5.4.288",
"versionStartIncluding": "3.3",
"vulnerable": true
},
{
"criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*",
"versionEndExcluding": "5.10.232",
"versionStartIncluding": "3.3",
"vulnerable": true
},
{
"criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*",
"versionEndExcluding": "5.15.175",
"versionStartIncluding": "3.3",
"vulnerable": true
},
{
"criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*",
"versionEndExcluding": "6.1.121",
"versionStartIncluding": "3.3",
"vulnerable": true
},
{
"criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*",
"versionEndExcluding": "6.6.67",
"versionStartIncluding": "3.3",
"vulnerable": true
},
{
"criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*",
"versionEndExcluding": "6.12.6",
"versionStartIncluding": "3.3",
"vulnerable": true
},
{
"criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*",
"versionEndExcluding": "6.13",
"versionStartIncluding": "3.3",
"vulnerable": true
}
],
"negate": false,
"operator": "OR"
}
]
}
],
"descriptions": [
{
"lang": "en",
"value": "In the Linux kernel, the following vulnerability has been resolved:\n\nnet/sched: netem: account for backlog updates from child qdisc\n\nIn general, \u0027qlen\u0027 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, \u0027qlen\u0027 only accounts for the packets in its internal\ntfifo. When netem is used with a child qdisc, the child qdisc can use\n\u0027qdisc_tree_reduce_backlog\u0027 to inform its parent, netem, about created\nor dropped SKBs. This function updates \u0027qlen\u0027 and the backlog statistics\nof netem, but netem does not account for changes made by a child qdisc.\n\u0027qlen\u0027 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\u0027s \u0027qlen\u0027 value is increased. When netem dequeues the\nnewly created SKBs from the child, the \u0027qlen\u0027 in netem is not updated.\nIf \u0027qlen\u0027 reaches the configured sch-\u003elimit, 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 \u003coif\u003e root handle 1: netem delay 100ms limit 100\n$ tc qdisc add dev \u003coif\u003e 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 \u003coif\u003e\n\nStatistics after 10s of iPerf3 TCP test before the fix (note that\nnetem\u0027s backlog \u003e 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\u0027s \u0027qlen\u0027.\nThe interface fully stops transferring packets and \"locks\". In this case,\nthe child qdisc and tfifo are empty, but \u0027qlen\u0027 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\u0027s \u0027qlen\u0027 is\nonly decreased when a packet is returned by its dequeue function, and not\nduring enqueuing into the child qdisc. External updates to \u0027qlen\u0027 are thus\naccounted for and only the behavior of the backlog statistics changes. As\nin other qdiscs, \u0027qlen\u0027 then keeps track of how many packets are held in\nnetem and all of its children. As before, sch-\u003elimit remains as the\nmaximum number of packets in the tfifo. The same applies to netem\u0027s\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"
}
}
}
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Drag nodes to arrange them. Double-click a related vulnerability to open it, or a source to visit its link. The Physics button on the left tunes the layout and the simulation; the legend at the bottom left hides or shows nodes by kind and by sighting type.
Experimental. This forecast is provided for visualization only and may change without notice. Do not use it for operational decisions.
Forecast uses a logistic model when the trend is rising, or an exponential decay model when the trend is falling. Fitted via linearized least squares.
Sightings
| Author | Source | Type | Date | Other |
|---|
Nomenclature
- Seen: The vulnerability was mentioned, discussed, or observed by the user.
- Confirmed: The vulnerability has been validated from an analyst's perspective.
- Published Proof of Concept: A public proof of concept is available for this vulnerability.
- Exploited: The vulnerability was observed as exploited by the user who reported the sighting.
- Patched: The vulnerability was observed as successfully patched by the user who reported the sighting.
- Not exploited: The vulnerability was not observed as exploited by the user who reported the sighting.
- Not confirmed: The user expressed doubt about the validity of the vulnerability.
- Not patched: The vulnerability was not observed as successfully patched by the user who reported the sighting.
Vulnerability timeline
Sightings and recorded dates, grouped by day · UTC
How durations are calculated
Following the VTEM framework (Black Hat USA 2015), time to patch starts when the vendor or a coordinator was informed, total time to patch at discovery, and disclosure to patch at public disclosure; vendor response time runs from the report to its acknowledgement. Time to exploit and time unpatched start at the earliest discovery or report, falling back to public disclosure. Unpatched time ends at the first recorded patch, or the calculation time when no patch is recorded. Exploitation to patch shows the interval between those two events; a published proof of concept is a public exploit, not exploitation.
Each result shows its source dates. A negative interval means the end event came first; when date-only inputs leave the order open, the result says so. Date-only inputs are approximate. The earliest evidence wins: KEV report dates and sightings are labelled as such. Records describing another vulnerability are listed but never calculated from, and a PoC alone does not establish exploitation. Missing patch evidence does not prove that no patch exists. Filters below change the event list only.
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The MITRE ATT&CK techniques below are AI-generated suggestions, inferred from the description of the
vulnerability by the CIRCL/vulnerability-attack-technique-classification-roberta-base
model, served locally by ML-Gateway.
They have not been verified by an analyst and are provided for guidance only.
The approach is described in our paper Mapping CVEs to MITRE ATT&CK Techniques: A Curated Gold-Set Classifier and the Limits of LLM-Assisted Label Expansion.
Browse all ATT&CK techniques and the vulnerabilities related to each.
The approach is described in our paper Mapping CVEs to MITRE ATT&CK Techniques: A Curated Gold-Set Classifier and the Limits of LLM-Assisted Label Expansion.
Browse all ATT&CK techniques and the vulnerabilities related to each.
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Related by attack behaviour
Vulnerabilities whose description is nearest to this one in the vector space of the CIRCL/vulnerability-attack-technique-biencoder model. This is a similarity search over the bi-encoder space (plain cosine), not a classification, and it has no measured accuracy.