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    SubjectRe: [PATCH v2 1/1] netfilter: nf_tables: fib: Drop IPV6 packages if IPv6 is disabled on boot
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    On Tue, 2019-08-27 at 12:35 +0200, Pablo Neira Ayuso wrote:
    > On Wed, Aug 21, 2019 at 11:15:06AM -0300, Leonardo Bras wrote:
    > > If IPv6 is disabled on boot (ipv6.disable=1), but nft_fib_inet ends up
    > > dealing with a IPv6 package, it causes a kernel panic in
    > > fib6_node_lookup_1(), crashing in bad_page_fault.
    >
    > Q: How do you get to see IPv6 packets if IPv6 module is disable?
    I could reproduce this bug on a host ('ipv6.disable=1') starting a
    guest with a virtio-net interface with 'filterref' over a virtual
    bridge. It crashes the host during guest boot (just before login).

    By that I could understand that a guest IPv6 network traffic (viavirtio-net) may cause this kernel panic.

    >
    > > The panic is caused by trying to deference a very low address (0x38
    > > in ppc64le), due to ipv6.fib6_main_tbl = NULL.
    > > BUG: Kernel NULL pointer dereference at 0x00000038
    > >
    > > Fix this behavior by dropping IPv6 packages if !ipv6_mod_enabled().
    >
    > I'd suggest: s/package/packet/
    Sure, I will make sure to put it on v3.
    (Sorry, I am not very used to net subsystem.)
    >
    > [...]
    > > diff --git a/net/ipv6/netfilter/nft_fib_ipv6.c b/net/ipv6/netfilter/nft_fib_ipv6.c
    > > index 7ece86afd079..75acc417e2ff 100644
    > > --- a/net/ipv6/netfilter/nft_fib_ipv6.c
    > > +++ b/net/ipv6/netfilter/nft_fib_ipv6.c
    > > @@ -125,6 +125,11 @@ void nft_fib6_eval_type(const struct nft_expr *expr, struct nft_regs *regs,
    > > u32 *dest = &regs->data[priv->dreg];
    > > struct ipv6hdr *iph, _iph;
    > >
    > > + if (!ipv6_mod_enabled()) {
    > > + regs->verdict.code = NF_DROP;
    >
    > NFT_BREAK instead to stop evaluating this rule, this results in a
    > mismatch, so you let the user decide what to do with packets that do
    > not match your policy.
    Ok, I will replace for v3.

    >
    > The drop case at the bottom of the fib eval function never actually
    > never happens.
    Which one do you mean?

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