From: Jiri Benc jbenc@redhat.com
[ Upstream commit 9e8acd9c44a0dd52b2922eeb82398c04e356c058 ]
The dst in bpf_input() has lwtstate field set. As it is of the LWTUNNEL_ENCAP_BPF type, lwtstate->data is struct bpf_lwt. When the bpf program returns BPF_LWT_REROUTE, ip_route_input_noref is directly called on this skb. This causes invalid memory access, as ip_route_input_slow calls skb_tunnel_info(skb) that expects the dst->lwstate->data to be struct ip_tunnel_info. This results to struct bpf_lwt being accessed as struct ip_tunnel_info.
Drop the dst before calling the IP route input functions (both for IPv4 and IPv6).
Reported by KASAN.
Fixes: 3bd0b15281af ("bpf: add handling of BPF_LWT_REROUTE to lwt_bpf.c") Signed-off-by: Jiri Benc jbenc@redhat.com Signed-off-by: Alexei Starovoitov ast@kernel.org Acked-by: Peter Oskolkov posk@google.com Link: https://lore.kernel.org/bpf/111664d58fe4e9dd9c8014bb3d0b2dab93086a9e.1570609... Signed-off-by: Sasha Levin sashal@kernel.org --- net/core/lwt_bpf.c | 7 ++++++- 1 file changed, 6 insertions(+), 1 deletion(-)
diff --git a/net/core/lwt_bpf.c b/net/core/lwt_bpf.c index f93785e5833c1..74cfb8b5ab330 100644 --- a/net/core/lwt_bpf.c +++ b/net/core/lwt_bpf.c @@ -88,11 +88,16 @@ static int bpf_lwt_input_reroute(struct sk_buff *skb) int err = -EINVAL;
if (skb->protocol == htons(ETH_P_IP)) { + struct net_device *dev = skb_dst(skb)->dev; struct iphdr *iph = ip_hdr(skb);
+ dev_hold(dev); + skb_dst_drop(skb); err = ip_route_input_noref(skb, iph->daddr, iph->saddr, - iph->tos, skb_dst(skb)->dev); + iph->tos, dev); + dev_put(dev); } else if (skb->protocol == htons(ETH_P_IPV6)) { + skb_dst_drop(skb); err = ipv6_stub->ipv6_route_input(skb); } else { err = -EAFNOSUPPORT;