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net/sched: Fix backlog accounting in qdisc_dequeue_internal

Type: advisorySource: Official CVE List1 source record

In the Linux kernel, the following vulnerability has been resolved: net/sched: Fix backlog accounting in qdisc_dequeue_internal This issue applies for the following qdiscs: hhf, fq, fq_codel, and fq_pie, and occurs in their change handlers when adjusting to the new limit. The problem is the following in the values passed to the subsequent qdisc_tree_reduce_backlog call given a tbf parent: When the tbf parent runs out of tokens, skbs of these qdiscs will be placed in gso_skb. Their peek handlers are qdisc_peek_dequeued, which accounts for both qlen and backlog. However, in the case of qdisc_dequeue_internal, ONLY qlen is accounted for when pulling from gso_skb. This means that these qdiscs are missing a qdisc_qstats_backlog_dec when dropping packets to satisfy the new limit in their change handlers. One can observe this issue with the following (with tc patched to support a limit of 0): export TARGET=fq tc qdisc del dev lo root tc qdisc add dev lo root handle 1: tbf rate 8bit burst 100b latency 1ms tc qdisc replace dev lo handle 3: parent 1:1 $TARGET limit 1000 echo ''; echo 'add child'; tc -s -d qdisc show dev lo ping -I lo -f -c2 -s32 -W0.001 127.0.0.1 2>&1 >/dev/null echo ''; echo 'after ping'; tc -s -d qdisc show dev lo tc qdisc change dev lo handle 3: parent 1:1 $TARGET limit 0 echo ''; echo 'after limit drop'; tc -s -d qdisc show dev lo tc qdisc replace dev lo handle 2: parent 1:1 sfq echo ''; echo 'post graft'; tc -s -d qdisc show dev lo The second to last show command

Announced Source revision 1
Original source ↗

CVE-2025-39677

Primary source · Revision 1

Imported from structured advisory data. Source references identify upstream records or fields; verify affected versions and your deployed configuration.

Security context

Source reference: cve:CVE-2025-39677

Linux

Source reference: /containers/cna/affected/0/product

Affected versions
Not stated in this record
Fixed versions
Not stated in this record
Prerequisites
Not stated in this record

Linux

Source reference: /containers/cna/affected/1/product

Affected versions
Not stated in this record
Fixed versions
Not stated in this record
Prerequisites
Not stated in this record

Structured affected-version data

Original package identities and version rules from this source.

[
  {
    "repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git",
    "vendor": "Linux",
    "product": "Linux",
    "versions": [
      {
        "status": "affected",
        "version": "4b549a2ef4bef9965d97cbd992ba67930cd3e0fe",
        "lessThan": "dcfed7251e23cd71d32c4ecc444ff97992087e46",
        "versionType": "git"
      },
      {
        "status": "affected",
        "version": "4b549a2ef4bef9965d97cbd992ba67930cd3e0fe",
        "lessThan": "38cdf8d1f5f3ee133f6e48dd422df4057fa9bfcb",
        "versionType": "git"
      },
      {
        "status": "affected",
        "version": "4b549a2ef4bef9965d97cbd992ba67930cd3e0fe",
        "lessThan": "a225f44d84b8900d679c5f5a9ea46fe9c0cc7802",
        "versionType": "git"
      },
      {
        "status": "affected",
        "version": "4b549a2ef4bef9965d97cbd992ba67930cd3e0fe",
        "lessThan": "52bf272636bda69587952b35ae97690b8dc89941",
        "versionType": "git"
      }
    ],
    "programFiles": [
      "include/net/sch_generic.h",
      "net/sched/sch_codel.c",
      "net/sched/sch_fq.c",
      "net/sched/sch_fq_codel.c",
      "net/sched/sch_fq_pie.c",
      "net/sched/sch_hhf.c",
      "net/sched/sch_pie.c"
    ],
    "defaultStatus": "unaffected"
  },
  {
    "repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git",
    "vendor": "Linux",
    "product": "Linux",
    "versions": [
      {
        "status": "affected",
        "version": "3.5"
      },
      {
        "status": "unaffected",
        "version": "0",
        "lessThan": "3.5",
        "versionType": "semver"
      },
      {
        "status": "unaffected",
        "version": "6.6.160",
        "versionType": "semver",
        "lessThanOrEqual": "6.6.*"
      },
      {
        "status": "unaffected",
        "version": "6.12.114",
        "versionType": "semver",
        "lessThanOrEqual": "6.12.*"
      },
      {
        "status": "unaffected",
        "version": "6.16.4",
        "versionType": "semver",
        "lessThanOrEqual": "6.16.*"
      },
      {
        "status": "unaffected",
        "version": "6.17",
        "versionType": "original_commit_for_fix",
        "lessThanOrEqual": "*"
      }
    ],
    "programFiles": [
      "include/net/sch_generic.h",
      "net/sched/sch_codel.c",
      "net/sched/sch_fq.c",
      "net/sched/sch_fq_codel.c",
      "net/sched/sch_fq_pie.c",
      "net/sched/sch_hhf.c",
      "net/sched/sch_pie.c"
    ],
    "defaultStatus": "affected"
  }
]
Related CVEs
CVE-2025-39677

Source reference: /cveMetadata/cveId

Publisher severity

high

Source reference: /containers/cna/metrics

Event
#46013 · Revision 1
Added to Heist Feed
Publisher date
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