CVE-2026-68337: bpf: Reject redirect helpers without a bpf_net_context

[Greg Kroah-Hartman <gregkh@linuxfoundation.org>]

From: Greg Kroah-Hartman <gregkh@kernel.org>

Description
===========

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

bpf: Reject redirect helpers without a bpf_net_context

The bpf_redirect*() helpers and skb_do_redirect() obtain the per-task
bpf_redirect_info via bpf_net_ctx_get_ri(), which dereferences the
current->bpf_net_context unconditionally. That context is established
on the paths that run tc BPF such as sch_handle_{ingress,egress}(),
*except* for the case where {cls,act}_bpf was attached to a proper
qdisc. A program running from there reaches the NULL deref in two ways:

* It calls bpf_redirect() directly, which dereferences the context at
  the top of the helper:

     tc qdisc add dev eth0 root handle 1: red limit 1MB min 10KB max 20KB \
        avpkt 1000 burst 100 qevent early_drop block 10
     tc filter add block 10 pref 1 bpf obj redirect.o

* It simply returns TC_ACT_REDIRECT without helper call: tcf_qevent_handle()
  then dispatches to skb_do_redirect(), which dereferences the context

Rather than extending bpf_net_context management into the qdisc path,
make the redirect helpers refuse to operate when no context exists, and
have tcf_qevent_handle() drop a TC_ACT_REDIRECT verdict instead of
calling skb_do_redirect(). Previous behaviour was a crash, so nothing
regresses by not supporting it.

The Linux kernel CVE team has assigned CVE-2026-68337 to this issue.


Affected and fixed versions
===========================

	Issue introduced in 5.9 with commit 3625750f05ecce21a0fce429c1ff85acfffb461b and fixed in 7.1.6 with commit cabfacbd5af09d3ae898ca224c4a1459e9bba15d
	Issue introduced in 5.9 with commit 3625750f05ecce21a0fce429c1ff85acfffb461b and fixed in 7.2-rc5 with commit 3f4920d165b29052255527d8ae7619e7ec132ece

Please see https://www.kernel.org for a full list of currently supported
kernel versions by the kernel community.

Unaffected versions might change over time as fixes are backported to
older supported kernel versions.  The official CVE entry at
	https://cve.org/CVERecord/?id=CVE-2026-68337
will be updated if fixes are backported, please check that for the most
up to date information about this issue.


Affected files
==============

The file(s) affected by this issue are:
	net/core/filter.c
	net/sched/cls_api.c


Mitigation
==========

The Linux kernel CVE team recommends that you update to the latest
stable kernel version for this, and many other bugfixes.  Individual
changes are never tested alone, but rather are part of a larger kernel
release.  Cherry-picking individual commits is not recommended or
supported by the Linux kernel community at all.  If however, updating to
the latest release is impossible, the individual changes to resolve this
issue can be found at these commits:
	https://git.kernel.org/stable/c/cabfacbd5af09d3ae898ca224c4a1459e9bba15d
	https://git.kernel.org/stable/c/3f4920d165b29052255527d8ae7619e7ec132ece