linux-kernel - Re: [next] BUG: kernel NULL pointer dereference, address:: selinux_ip_postroute

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Date:   Tue, 19 Oct 2021 15:10:49 +0200
From:   Florian Westphal <fw@...len.de>
To:     Naresh Kamboju <naresh.kamboju@...aro.org>
Cc:     open list <linux-kernel@...r.kernel.org>, selinux@...r.kernel.org,
        Linux-Next Mailing List <linux-next@...r.kernel.org>,
        Netdev <netdev@...r.kernel.org>, lkft-triage@...ts.linaro.org,
        Florian Westphal <fw@...len.de>,
        Paul Moore <paul@...l-moore.com>,
        Eric Paris <eparis@...isplace.org>,
        Stephen Smalley <stephen.smalley.work@...il.com>,
        Stephen Rothwell <sfr@...b.auug.org.au>
Subject: Re: [next] BUG: kernel NULL pointer dereference, address::
 selinux_ip_postroute_compat

Naresh Kamboju <naresh.kamboju@...aro.org> wrote:
> Following kernel crash noticed on linux next 20211019 tag.
> on x86, i386 and other architectures.

Paul, this might be caused by
1d1e1ded13568be81a0e19d228e310a48997bec8
("selinux: make better use of the nf_hook_state passed to the NF
 hooks"), in particular this hunk here:

-       if (sk == NULL)
+       if (state->sk == NULL)
                return NF_ACCEPT;
+       sk = skb_to_full_sk(skb);
        sksec = sk->sk_security;

state->sk might not be related to skb->sk.
I suspect that this should instead be:

+       sk = skb_to_full_sk(skb);
        if (sk == NULL)

See 7026b1ddb6b8d4e6ee33dc2bd06c0ca8746fa7ab for the origin of this
additional socket pointer.