This is a note to let you know that I've just added the patch titled net, bpf: Fix ip6ip6 crash with collect_md populated skbs to the 5.11-stable tree which can be found at: http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary The filename of the patch is: net-bpf-fix-ip6ip6-crash-with-collect_md-populated-s.patch and it can be found in the queue-5.11 subdirectory. If you, or anyone else, feels it should not be added to the stable tree, please let <stable@xxxxxxxxxxxxxxx> know about it. commit 84c0068ca83ee33f07fe9a1b2d4f0f648dff9c8d Author: Daniel Borkmann <daniel@xxxxxxxxxxxxx> Date: Wed Mar 10 01:38:10 2021 +0100 net, bpf: Fix ip6ip6 crash with collect_md populated skbs [ Upstream commit a188bb5638d41aa99090ebf2f85d3505ab13fba5 ] 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@xxxxxxxxxxxxx> Signed-off-by: David S. Miller <davem@xxxxxxxxxxxxx> Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx> 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; }