The patch below does not apply to the 4.9-stable tree. If someone wants it applied there, or to any other stable or longterm tree, then please email the backport, including the original git commit id to stable@vger.kernel.org.

Thanks, Sasha

------------------ original commit in Linus's tree ------------------

From a188bb5638d41aa99090ebf2f85d3505ab13fba5 Mon Sep 17 00:00:00 2001

From: Daniel Borkmann daniel@iogearbox.net Date: Wed, 10 Mar 2021 01:38:10 +0100 Subject: [PATCH] net, bpf: Fix ip6ip6 crash with collect_md populated skbs

I ran into a crash where setting up a ip6ip6 tunnel device which was /not/ set to collect_md mode was receiving collect_md populated skbs for xmit.

The BPF prog was populating the skb via bpf_skb_set_tunnel_key() which is assigning special metadata dst entry and then redirecting the skb to the device, taking ip6_tnl_start_xmit() -> ipxip6_tnl_xmit() -> ip6_tnl_xmit() and in the latter it performs a neigh lookup based on skb_dst(skb) where we trigger a NULL pointer dereference on dst->ops->neigh_lookup() since the md_dst_ops do not populate neigh_lookup callback with a fake handler.

Transform the md_dst_ops into generic dst_blackhole_ops that can also be reused elsewhere when needed, and use them for the metadata dst entries as callback ops.

Also, remove the dst_md_discard{,_out}() ops and rely on dst_discard{,_out}() from dst_init() which free the skb the same way modulo the splat. Given we will be able to recover just fine from there, avoid any potential splats iff this gets ever triggered in future (or worse, panic on warns when set).

Fixes: f38a9eb1f77b ("dst: Metadata destinations") Signed-off-by: Daniel Borkmann daniel@iogearbox.net Signed-off-by: David S. Miller davem@davemloft.net --- net/core/dst.c | 31 +++++++++---------------------- 1 file changed, 9 insertions(+), 22 deletions(-)

diff --git a/net/core/dst.c b/net/core/dst.c index 5f6315601776..fb3bcba87744 100644 --- a/net/core/dst.c +++ b/net/core/dst.c @@ -275,37 +275,24 @@ unsigned int dst_blackhole_mtu(const struct dst_entry *dst) } EXPORT_SYMBOL_GPL(dst_blackhole_mtu);

-static struct dst_ops md_dst_ops = { - .family = AF_UNSPEC, +static struct dst_ops dst_blackhole_ops = { + .family = AF_UNSPEC, + .neigh_lookup = dst_blackhole_neigh_lookup, + .check = dst_blackhole_check, + .cow_metrics = dst_blackhole_cow_metrics, + .update_pmtu = dst_blackhole_update_pmtu, + .redirect = dst_blackhole_redirect, + .mtu = dst_blackhole_mtu, };

-static int dst_md_discard_out(struct net *net, struct sock *sk, struct sk_buff *skb) -{ - WARN_ONCE(1, "Attempting to call output on metadata dst\n"); - kfree_skb(skb); - return 0; -} - -static int dst_md_discard(struct sk_buff *skb) -{ - WARN_ONCE(1, "Attempting to call input on metadata dst\n"); - kfree_skb(skb); - return 0; -} - static void __metadata_dst_init(struct metadata_dst *md_dst, enum metadata_type type, u8 optslen) - { struct dst_entry *dst;

dst = &md_dst->dst; - dst_init(dst, &md_dst_ops, NULL, 1, DST_OBSOLETE_NONE, + dst_init(dst, &dst_blackhole_ops, NULL, 1, DST_OBSOLETE_NONE, DST_METADATA | DST_NOCOUNT); - - dst->input = dst_md_discard; - dst->output = dst_md_discard_out; - memset(dst + 1, 0, sizeof(*md_dst) + optslen - sizeof(*dst)); md_dst->type = type; }