net/sched: netem: account for backlog updates from child qdisc

MITRE NVD CVE.ORG JSON API

Summary

CVECVE-2024-56770
StatePUBLISHED
AssignerLinux
Source PriorityCVE Program / NVD first with legacy fallback
Published2025-01-08 17:15:15 UTC
Updated2026-10-15 02:17:10 UTC
DescriptionIn 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.

Risk And Classification

Primary CVSS: v3.1 5.5 MEDIUM from [email protected]

CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H

Problem Types: NVD-CWE-noinfo | CWE-noinfo Not enough information

VersionSourceTypeScoreSeverityVector
3.1[email protected]Primary5.5MEDIUMCVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H
3.1ADPDECLARED5.5MEDIUMCVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H
3.1134c704f-9b21-4f2e-91b3-4a467353bcc0Secondary5.5MEDIUMCVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H

CVSS v3.1 Breakdown

Attack Vector
Local
Attack Complexity
Low
Privileges Required
Low
User Interaction
None
Scope
Unchanged
Confidentiality
None
Integrity
None
Availability
High

CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H

NVD Known Affected Configurations (CPE 2.3)

TypeVendorProductVersionUpdateEditionLanguage
Operating System Linux Linux Kernel All All All All

Vendor Declared Affected Products

SourceVendorProductVersionPlatforms
CNA Linux Linux affected 50612537e9ab29693122fab20fc1eed235054ffe 83c6ab12f08dcc09d4c5ac86fdb89736b28f1d31 git Not specified
CNA Linux Linux affected 50612537e9ab29693122fab20fc1eed235054ffe 216509dda290f6db92c816dd54b83c1df9da9e76 git Not specified
CNA Linux Linux affected 50612537e9ab29693122fab20fc1eed235054ffe c2047b0e216c8edce227d7c42f99ac2877dad0e4 git Not specified
CNA Linux Linux affected 50612537e9ab29693122fab20fc1eed235054ffe 10df49cfca73dfbbdb6c4150d859f7e8926ae427 git Not specified
CNA Linux Linux affected 50612537e9ab29693122fab20fc1eed235054ffe 3824c5fad18eeb7abe0c4fc966f29959552dca3e git Not specified
CNA Linux Linux affected 50612537e9ab29693122fab20fc1eed235054ffe 356078a5c55ec8d2061fcc009fb8599f5b0527f9 git Not specified
CNA Linux Linux affected 50612537e9ab29693122fab20fc1eed235054ffe f8d4bc455047cf3903cd6f85f49978987dbb3027 git Not specified
CNA Linux Linux affected 3.3 Not specified
CNA Linux Linux unaffected 3.3 semver Not specified
CNA Linux Linux unaffected 5.4.288 5.4.* semver Not specified
CNA Linux Linux unaffected 5.10.232 5.10.* semver Not specified
CNA Linux Linux unaffected 5.15.175 5.15.* semver Not specified
CNA Linux Linux unaffected 6.1.121 6.1.* semver Not specified
CNA Linux Linux unaffected 6.6.67 6.6.* semver Not specified
CNA Linux Linux unaffected 6.12.6 6.12.* semver Not specified
CNA Linux Linux unaffected 6.13 * original_commit_for_fix Not specified
ADP Siemens SIMATIC S7-1500 CPU 1518-4 PN/DP MFP affected V3.1.0 V3.1.5 custom Not specified
ADP Siemens SIMATIC S7-1500 CPU 1518-4 PN/DP MFP affected V3.1.0 V3.1.5 custom Not specified
ADP Siemens SIMATIC S7-1500 CPU 1518F-4 PN/DP MFP affected V3.1.0 V3.1.5 custom Not specified
ADP Siemens SIMATIC S7-1500 CPU 1518F-4 PN/DP MFP affected V3.1.0 V3.1.5 custom Not specified
ADP Siemens SIPLUS S7-1500 CPU 1518-4 PN/DP MFP affected V3.1.0 V3.1.5 custom Not specified
ADP Siemens RUGGEDCOM RST2428P affected V3.2 custom Not specified
ADP Siemens SCALANCE XC-300/XR-300/XC-400/XR-500WG/XR-500 Family affected V3.2 custom Not specified
ADP Siemens SCALANCE XCM-/XRM-/XCH-/XRH-300 Family affected V3.2 custom Not specified

References

ReferenceSourceLinkTags
cert-portal.siemens.com/productcert/html/ssa-398330.html 0b142b55-0307-4c5a-b3c9-f314f3fb7c5e cert-portal.siemens.com
lists.debian.org/debian-lts-announce/2025/03/msg00002.html af854a3a-2127-422b-91ae-364da2661108 lists.debian.org
git.kernel.org/stable/c/83c6ab12f08dcc09d4c5ac86fdb89736b28f1d31 416baaa9-dc9f-4396-8d5f-8c081fb06d67 git.kernel.org Patch
git.kernel.org/stable/c/3824c5fad18eeb7abe0c4fc966f29959552dca3e 416baaa9-dc9f-4396-8d5f-8c081fb06d67 git.kernel.org Patch
git.kernel.org/stable/c/356078a5c55ec8d2061fcc009fb8599f5b0527f9 416baaa9-dc9f-4396-8d5f-8c081fb06d67 git.kernel.org Patch
git.kernel.org/stable/c/f8d4bc455047cf3903cd6f85f49978987dbb3027 416baaa9-dc9f-4396-8d5f-8c081fb06d67 git.kernel.org Patch
git.kernel.org/stable/c/c2047b0e216c8edce227d7c42f99ac2877dad0e4 416baaa9-dc9f-4396-8d5f-8c081fb06d67 git.kernel.org Patch
lists.debian.org/debian-lts-announce/2025/03/msg00001.html af854a3a-2127-422b-91ae-364da2661108 lists.debian.org
git.kernel.org/stable/c/10df49cfca73dfbbdb6c4150d859f7e8926ae427 416baaa9-dc9f-4396-8d5f-8c081fb06d67 git.kernel.org Patch
cert-portal.siemens.com/productcert/html/ssa-355557.html 0b142b55-0307-4c5a-b3c9-f314f3fb7c5e cert-portal.siemens.com
git.kernel.org/stable/c/216509dda290f6db92c816dd54b83c1df9da9e76 416baaa9-dc9f-4396-8d5f-8c081fb06d67 git.kernel.org Patch
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