net/sched: Fix backlog accounting in qdisc_dequeue_internal
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
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