net/sched: cls_fw: fix NULL pointer dereference on shared blocks
In the Linux kernel, the following vulnerability has been resolved: net/sched: cls_fw: fix NULL pointer dereference on shared blocks The old-method path in fw_classify() calls tcf_block_q() and dereferences q->handle. Shared blocks leave block->q NULL, causing a NULL deref when an empty cls_fw filter is attached to a shared block and a packet with a nonzero major skb mark is classified. Reject the configuration in fw_change() when the old method (no TCA_OPTIONS) is used on a shared block, since fw_classify()'s old-method path needs block->q which is NULL for shared blocks. The fixed null-ptr-deref calling stack: KASAN: null-ptr-deref in range [0x0000000000000038-0x000000000000003f] RIP: 0010:fw_classify (net/sched/cls_fw.c:81) Call Trace: tcf_classify (./include/net/tc_wrapper.h:197 net/sched/cls_api.c:1764 net/sched/cls_api.c:1860) tc_run (net/core/dev.c:4401) __dev_queue_xmit (net/core/dev.c:4535 net/core/dev.c:4790)
CVE-2026-31421
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-2026-31421
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": "1abf272022cf1d18469405f47b4ec49c6a3125db",
"lessThan": "d6d5bd62a09650856e1e2010eb09853eba0d64e1",
"versionType": "git"
},
{
"status": "affected",
"version": "1abf272022cf1d18469405f47b4ec49c6a3125db",
"lessThan": "febf64ca79a2d6540ab6e5e197fa0f4f7e84473e",
"versionType": "git"
},
{
"status": "affected",
"version": "1abf272022cf1d18469405f47b4ec49c6a3125db",
"lessThan": "3d41f9a314afa94b1c7c7c75405920123220e8cd",
"versionType": "git"
},
{
"status": "affected",
"version": "1abf272022cf1d18469405f47b4ec49c6a3125db",
"lessThan": "18328eff2f97d1a6adcdb6d4a0f42f2f83a31e28",
"versionType": "git"
},
{
"status": "affected",
"version": "1abf272022cf1d18469405f47b4ec49c6a3125db",
"lessThan": "5cf41031922c154aa5ccda8bcdb0f5e6226582ec",
"versionType": "git"
},
{
"status": "affected",
"version": "1abf272022cf1d18469405f47b4ec49c6a3125db",
"lessThan": "3cb055df9e8625ce699a259d8178d67b37f2b160",
"versionType": "git"
},
{
"status": "affected",
"version": "1abf272022cf1d18469405f47b4ec49c6a3125db",
"lessThan": "96426c348def662b06bfdc65be3002905604927a",
"versionType": "git"
},
{
"status": "affected",
"version": "1abf272022cf1d18469405f47b4ec49c6a3125db",
"lessThan": "faeea8bbf6e958bf3c00cb08263109661975987c",
"versionType": "git"
}
],
"programFiles": [
"net/sched/cls_fw.c"
],
"defaultStatus": "unaffected"
},
{
"repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git",
"vendor": "Linux",
"product": "Linux",
"versions": [
{
"status": "affected",
"version": "4.15"
},
{
"status": "unaffected",
"version": "0",
"lessThan": "4.15",
"versionType": "semver"
},
{
"status": "unaffected",
"version": "5.10.253",
"versionType": "semver",
"lessThanOrEqual": "5.10.*"
},
{
"status": "unaffected",
"version": "5.15.203",
"versionType": "semver",
"lessThanOrEqual": "5.15.*"
},
{
"status": "unaffected",
"version": "6.1.168",
"versionType": "semver",
"lessThanOrEqual": "6.1.*"
},
{
"status": "unaffected",
"version": "6.6.134",
"versionType": "semver",
"lessThanOrEqual": "6.6.*"
},
{
"status": "unaffected",
"version": "6.12.81",
"versionType": "semver",
"lessThanOrEqual": "6.12.*"
},
{
"status": "unaffected",
"version": "6.18.22",
"versionType": "semver",
"lessThanOrEqual": "6.18.*"
},
{
"status": "unaffected",
"version": "6.19.12",
"versionType": "semver",
"lessThanOrEqual": "6.19.*"
},
{
"status": "unaffected",
"version": "7.0",
"versionType": "original_commit_for_fix",
"lessThanOrEqual": "*"
}
],
"programFiles": [
"net/sched/cls_fw.c"
],
"defaultStatus": "affected"
}
]- Related CVEs
- CVE-2026-31421
Source reference:
/cveMetadata/cveId
Publisher severity
No explicit severity was provided.
- Event
- #28272 · Revision 1
- Added to Heist Feed
- Publisher date