bpf: handle GSO in bpf_lwt_push_encap

This patch adds handling of GSO packets in bpf_lwt_push_ip_encap()
(called from bpf_lwt_push_encap):

* IPIP, GRE, and UDP encapsulation types are deduced by looking
  into iphdr->protocol or ipv6hdr->next_header;
* SCTP GSO packets are not supported (as bpf_skb_proto_4_to_6
  and similar do);
* UDP_L4 GSO packets are also not supported (although they are
  not blocked in bpf_skb_proto_4_to_6 and similar), as
  skb_decrease_gso_size() will break it;
* SKB_GSO_DODGY bit is set.

Note: it may be possible to support SCTP and UDP_L4 gso packets;
      but as these cases seem to be not well handled by other
      tunneling/encapping code paths, the solution should
      be generic enough to apply to all tunneling/encapping code.

v8 changes:
   - make sure that if GRE or UDP encap is detected, there is
     enough of pushed bytes to cover both IP[v6] + GRE|UDP headers;
   - do not reject double-encapped packets;
   - whitelist TCP GSO packets rather than block SCTP GSO and
     UDP GSO.

Signed-off-by: Peter Oskolkov <posk@google.com>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>

diff --git a/net/core/lwt_bpf.c b/net/core/lwt_bpf.c
index e5a9850..079871f 100644 (file)
--- a/net/core/lwt_bpf.c
+++ b/net/core/lwt_bpf.c
@@ -16,6 +16,7 @@
 #include <linux/types.h>
 #include <linux/bpf.h>
 #include <net/lwtunnel.h>
+#include <net/gre.h>
 
 struct bpf_lwt_prog {
        struct bpf_prog *prog;
@@ -390,10 +391,72 @@ static const struct lwtunnel_encap_ops bpf_encap_ops = {
        .owner          = THIS_MODULE,
 };
 
+static int handle_gso_type(struct sk_buff *skb, unsigned int gso_type,
+                          int encap_len)
+{
+       struct skb_shared_info *shinfo = skb_shinfo(skb);
+
+       gso_type |= SKB_GSO_DODGY;
+       shinfo->gso_type |= gso_type;
+       skb_decrease_gso_size(shinfo, encap_len);
+       shinfo->gso_segs = 0;
+       return 0;
+}
+
 static int handle_gso_encap(struct sk_buff *skb, bool ipv4, int encap_len)
 {
-       /* Handling of GSO-enabled packets is added in the next patch. */
-       return -EOPNOTSUPP;
+       int next_hdr_offset;
+       void *next_hdr;
+       __u8 protocol;
+
+       /* SCTP and UDP_L4 gso need more nuanced handling than what
+        * handle_gso_type() does above: skb_decrease_gso_size() is not enough.
+        * So at the moment only TCP GSO packets are let through.
+        */
+       if (!(skb_shinfo(skb)->gso_type & (SKB_GSO_TCPV4 | SKB_GSO_TCPV6)))
+               return -ENOTSUPP;
+
+       if (ipv4) {
+               protocol = ip_hdr(skb)->protocol;
+               next_hdr_offset = sizeof(struct iphdr);
+               next_hdr = skb_network_header(skb) + next_hdr_offset;
+       } else {
+               protocol = ipv6_hdr(skb)->nexthdr;
+               next_hdr_offset = sizeof(struct ipv6hdr);
+               next_hdr = skb_network_header(skb) + next_hdr_offset;
+       }
+
+       switch (protocol) {
+       case IPPROTO_GRE:
+               next_hdr_offset += sizeof(struct gre_base_hdr);
+               if (next_hdr_offset > encap_len)
+                       return -EINVAL;
+
+               if (((struct gre_base_hdr *)next_hdr)->flags & GRE_CSUM)
+                       return handle_gso_type(skb, SKB_GSO_GRE_CSUM,
+                                              encap_len);
+               return handle_gso_type(skb, SKB_GSO_GRE, encap_len);
+
+       case IPPROTO_UDP:
+               next_hdr_offset += sizeof(struct udphdr);
+               if (next_hdr_offset > encap_len)
+                       return -EINVAL;
+
+               if (((struct udphdr *)next_hdr)->check)
+                       return handle_gso_type(skb, SKB_GSO_UDP_TUNNEL_CSUM,
+                                              encap_len);
+               return handle_gso_type(skb, SKB_GSO_UDP_TUNNEL, encap_len);
+
+       case IPPROTO_IP:
+       case IPPROTO_IPV6:
+               if (ipv4)
+                       return handle_gso_type(skb, SKB_GSO_IPXIP4, encap_len);
+               else
+                       return handle_gso_type(skb, SKB_GSO_IPXIP6, encap_len);
+
+       default:
+               return -EPROTONOSUPPORT;
+       }
 }
 
 int bpf_lwt_push_ip_encap(struct sk_buff *skb, void *hdr, u32 len, bool ingress)