CVE-2026-31422

In the Linux kernel, the following vulnerability has been resolved:

net/sched: cls_flow: fix NULL pointer dereference on shared blocks

flow_change() calls tcf_block_q() and dereferences q->handle to derive

a default baseclass. Shared blocks leave block->q NULL, causing a NULL

deref when a flow filter without a fully qualified baseclass is created

on a shared block.

Check tcf_block_shared() before accessing block->q and return -EINVAL

for shared blocks. This avoids the null-deref shown below:

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KASAN: null-ptr-deref in range [0x0000000000000038-0x000000000000003f]

RIP: 0010:flow_change (net/sched/cls_flow.c:508)

Call Trace:

tc_new_tfilter (net/sched/cls_api.c:2432)

rtnetlink_rcv_msg (net/core/rtnetlink.c:6980)

[...]

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