EUVD-2026-21945
GHSA-pmqm-g7jm-76hf
CVSS VectorNVD
CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H
Lifecycle Timeline
6DescriptionNVD
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)
AnalysisAI
NULL pointer dereference in the Linux kernel's cls_fw traffic classifier (net/sched/cls_fw.c) crashes the kernel when authenticated local users configure an old-method cls_fw filter on a shared tc block and traffic with a nonzero major skb mark is processed. The flaw exists because the old classification path in fw_classify() calls tcf_block_q() and dereferences q->handle, but shared blocks hold a NULL block->q pointer. …
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