CVE-2025-39766 (GCVE-0-2025-39766)

Vulnerability from cvelistv5 – Published: 2025-09-11 16:56 – Updated: 2025-11-03 17:43
VLAI?
Title
net/sched: Make cake_enqueue return NET_XMIT_CN when past buffer_limit
Summary
In the Linux kernel, the following vulnerability has been resolved: net/sched: Make cake_enqueue return NET_XMIT_CN when past buffer_limit The following setup can trigger a WARNING in htb_activate due to the condition: !cl->leaf.q->q.qlen tc qdisc del dev lo root tc qdisc add dev lo root handle 1: htb default 1 tc class add dev lo parent 1: classid 1:1 \ htb rate 64bit tc qdisc add dev lo parent 1:1 handle f: \ cake memlimit 1b ping -I lo -f -c1 -s64 -W0.001 127.0.0.1 This is because the low memlimit leads to a low buffer_limit, which causes packet dropping. However, cake_enqueue still returns NET_XMIT_SUCCESS, causing htb_enqueue to call htb_activate with an empty child qdisc. We should return NET_XMIT_CN when packets are dropped from the same tin and flow. I do not believe return value of NET_XMIT_CN is necessary for packet drops in the case of ack filtering, as that is meant to optimize performance, not to signal congestion.
Severity ?
No CVSS data available.
Assigner
References
Impacted products
Vendor Product Version
Linux Linux Affected: 046f6fd5daefac7f5abdafb436b30f63bc7c602b , < 7689ab22de36f8db19095f6bdf11f28cfde92f5c (git)
Affected: 046f6fd5daefac7f5abdafb436b30f63bc7c602b , < de04ddd2980b48caa8d7e24a7db2742917a8b280 (git)
Affected: 046f6fd5daefac7f5abdafb436b30f63bc7c602b , < 0dacfc5372e314d1219f03e64dde3ab495a5a25e (git)
Affected: 046f6fd5daefac7f5abdafb436b30f63bc7c602b , < 710866fc0a64eafcb8bacd91bcb1329eb7e5035f (git)
Affected: 046f6fd5daefac7f5abdafb436b30f63bc7c602b , < aa12ee1c1bd260943fd6ab556d8635811c332eeb (git)
Affected: 046f6fd5daefac7f5abdafb436b30f63bc7c602b , < ff57186b2cc39766672c4c0332323933e5faaa88 (git)
Affected: 046f6fd5daefac7f5abdafb436b30f63bc7c602b , < 62d591dde4defb1333d202410609c4ddeae060b3 (git)
Affected: 046f6fd5daefac7f5abdafb436b30f63bc7c602b , < 15de71d06a400f7fdc15bf377a2552b0ec437cf5 (git)
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    Linux Linux Affected: 4.19
Unaffected: 0 , < 4.19 (semver)
Unaffected: 5.4.297 , ≤ 5.4.* (semver)
Unaffected: 5.10.241 , ≤ 5.10.* (semver)
Unaffected: 5.15.190 , ≤ 5.15.* (semver)
Unaffected: 6.1.149 , ≤ 6.1.* (semver)
Unaffected: 6.6.103 , ≤ 6.6.* (semver)
Unaffected: 6.12.44 , ≤ 6.12.* (semver)
Unaffected: 6.16.4 , ≤ 6.16.* (semver)
Unaffected: 6.17 , ≤ * (original_commit_for_fix)
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          "value": "In the Linux kernel, the following vulnerability has been resolved:\n\nnet/sched: Make cake_enqueue return NET_XMIT_CN when past buffer_limit\n\nThe following setup can trigger a WARNING in htb_activate due to\nthe condition: !cl-\u003eleaf.q-\u003eq.qlen\n\ntc qdisc del dev lo root\ntc qdisc add dev lo root handle 1: htb default 1\ntc class add dev lo parent 1: classid 1:1 \\\n       htb rate 64bit\ntc qdisc add dev lo parent 1:1 handle f: \\\n       cake memlimit 1b\nping -I lo -f -c1 -s64 -W0.001 127.0.0.1\n\nThis is because the low memlimit leads to a low buffer_limit, which\ncauses packet dropping. However, cake_enqueue still returns\nNET_XMIT_SUCCESS, causing htb_enqueue to call htb_activate with an\nempty child qdisc. We should return NET_XMIT_CN when packets are\ndropped from the same tin and flow.\n\nI do not believe return value of NET_XMIT_CN is necessary for packet\ndrops in the case of ack filtering, as that is meant to optimize\nperformance, not to signal congestion."
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