[PATCH 1/1] netfilter: nf_tables: fib: Drop IPV6 packages if IPv6 is disabled on boot

[PATCH 1/1] netfilter: nf_tables: fib: Drop IPV6 packages if IPv6 is disabled on boot

[Leonardo Bras]

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.

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().

Signed-off-by: Leonardo Bras <leonardo@linux.ibm.com>
---
 net/netfilter/nft_fib_inet.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/net/netfilter/nft_fib_inet.c b/net/netfilter/nft_fib_inet.c
index 465432e0531b..0017afab3c51 100644
--- a/net/netfilter/nft_fib_inet.c
+++ b/net/netfilter/nft_fib_inet.c
@@ -2,6 +2,7 @@
 
 #include <linux/kernel.h>
 #include <linux/init.h>
+#include <linux/ipv6.h>
 #include <linux/module.h>
 #include <linux/netlink.h>
 #include <linux/netfilter.h>
@@ -28,6 +29,8 @@ static void nft_fib_inet_eval(const struct nft_expr *expr,
 		}
 		break;
 	case NFPROTO_IPV6:
+		if (!ipv6_mod_enabled())
+			break;
 		switch (priv->result) {
 		case NFT_FIB_RESULT_OIF:
 		case NFT_FIB_RESULT_OIFNAME:
-- 
2.20.1

Re: [PATCH 1/1] netfilter: nf_tables: fib: Drop IPV6 packages if IPv6 is disabled on boot

[Florian Westphal]

Leonardo Bras <leonardo@linux.ibm.com> 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.
> 
> 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().

Wouldn't fib_netdev.c have the same problem?

If so, might be better to place this test in both
nft_fib6_eval_type and nft_fib6_eval.

Re: [PATCH 1/1] netfilter: nf_tables: fib: Drop IPV6 packages if IPv6 is disabled on boot

[Leonardo Bras]

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On Tue, 2019-08-20 at 07:36 +0200, Florian Westphal wrote:
> Wouldn't fib_netdev.c have the same problem?
Probably, but I haven't hit this issue yet.

> If so, might be better to place this test in both
> nft_fib6_eval_type and nft_fib6_eval.
I think that is possible, and not very hard to do.

But in my humble viewpoint, it looks like it's nft_fib_inet_eval() and
nft_fib_netdev_eval() have the responsibility to choose a valid
protocol or drop the package. 
I am not sure if it would be a good move to transfer this
responsibility to nft_fib6_eval_type() and nft_fib6_eval(), so I would
rather add the same test to nft_fib_netdev_eval().

Does it make sense?

Thanks for the feedback!

Leonardo Bras


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Re: [PATCH 1/1] netfilter: nf_tables: fib: Drop IPV6 packages if IPv6 is disabled on boot

[Pablo Neira Ayuso]

On Tue, Aug 20, 2019 at 01:15:58PM -0300, Leonardo Bras wrote:
> On Tue, 2019-08-20 at 07:36 +0200, Florian Westphal wrote:
> > Wouldn't fib_netdev.c have the same problem?
> Probably, but I haven't hit this issue yet.
> 
> > If so, might be better to place this test in both
> > nft_fib6_eval_type and nft_fib6_eval.
>
> I think that is possible, and not very hard to do.
> 
> But in my humble viewpoint, it looks like it's nft_fib_inet_eval() and
> nft_fib_netdev_eval() have the responsibility to choose a valid
> protocol or drop the package. 
> I am not sure if it would be a good move to transfer this
> responsibility to nft_fib6_eval_type() and nft_fib6_eval(), so I would
> rather add the same test to nft_fib_netdev_eval().
> 
> Does it make sense?

Please, update common code to netdev and ip6 extensions as Florian
suggests.

Thanks.

Re: [PATCH 1/1] netfilter: nf_tables: fib: Drop IPV6 packages if IPv6 is disabled on boot

[Leonardo Bras]

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On Wed, 2019-08-21 at 11:58 +0200, Pablo Neira Ayuso wrote:
> On Tue, Aug 20, 2019 at 01:15:58PM -0300, Leonardo Bras wrote:
> > On Tue, 2019-08-20 at 07:36 +0200, Florian Westphal wrote:
> > > Wouldn't fib_netdev.c have the same problem?
> > Probably, but I haven't hit this issue yet.
> > 
> > > If so, might be better to place this test in both
> > > nft_fib6_eval_type and nft_fib6_eval.
> > 
> > I think that is possible, and not very hard to do.
> > 
> > But in my humble viewpoint, it looks like it's nft_fib_inet_eval() and
> > nft_fib_netdev_eval() have the responsibility to choose a valid
> > protocol or drop the package. 
> > I am not sure if it would be a good move to transfer this
> > responsibility to nft_fib6_eval_type() and nft_fib6_eval(), so I would
> > rather add the same test to nft_fib_netdev_eval().
> > 
> > Does it make sense?
> 
> Please, update common code to netdev and ip6 extensions as Florian
> suggests.
> 
> Thanks.

Ok then, I will send a v2 with that change.

Thanks,

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Re: [PATCH 1/1] netfilter: nf_tables: fib: Drop IPV6 packages if IPv6 is disabled on boot

[Leonardo Bras]

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Hello Pablo, Florian,

I implemented a V2 of this patch with the changes you proposed.
Could you please give your feedback on that patch?
https://lkml.org/lkml/2019/8/21/527

Thanks!

On Wed, 2019-08-21 at 11:58 +0200, Pablo Neira Ayuso wrote:
> On Tue, Aug 20, 2019 at 01:15:58PM -0300, Leonardo Bras wrote:
> > On Tue, 2019-08-20 at 07:36 +0200, Florian Westphal wrote:
> > > Wouldn't fib_netdev.c have the same problem?
> > Probably, but I haven't hit this issue yet.
> > 
> > > If so, might be better to place this test in both
> > > nft_fib6_eval_type and nft_fib6_eval.
> > 
> > I think that is possible, and not very hard to do.
> > 
> > But in my humble viewpoint, it looks like it's nft_fib_inet_eval() and
> > nft_fib_netdev_eval() have the responsibility to choose a valid
> > protocol or drop the package. 
> > I am not sure if it would be a good move to transfer this
> > responsibility to nft_fib6_eval_type() and nft_fib6_eval(), so I would
> > rather add the same test to nft_fib_netdev_eval().
> > 
> > Does it make sense?
> 
> Please, update common code to netdev and ip6 extensions as Florian
> suggests.
> 
> Thanks.

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