Re: [PATCH v2 net-next 4/6] udp: flow dissector offload

On Wed, Aug 30, 2017 at 6:36 AM, Paolo Abeni [off-list ref] wrote:

On Tue, 2017-08-29 at 16:27 -0700, Tom Herbert wrote:

quoted

Add support to perform UDP specific flow dissection. This is
primarily intended for dissecting encapsulated packets in UDP
encapsulation.

This patch adds a flow_dissect offload for UDP4 and UDP6. The backend
function performs a socket lookup and calls the flow_dissect function
if a socket is found.

Signed-off-by: Tom Herbert <redacted>
---
 include/linux/udp.h      |  8 ++++++++
 include/net/udp.h        |  8 ++++++++
 include/net/udp_tunnel.h |  8 ++++++++
 net/ipv4/udp_offload.c   | 45 +++++++++++++++++++++++++++++++++++++++++++++
 net/ipv4/udp_tunnel.c    |  1 +
 net/ipv6/udp_offload.c   | 13 +++++++++++++
 6 files changed, 83 insertions(+)

diff --git a/include/linux/udp.h b/include/linux/udp.h
index eaea63bc79bb..2e90b189ef6a 100644
--- a/include/linux/udp.h
+++ b/include/linux/udp.h

@@ -79,6 +79,14 @@ struct udp_sock {
      int                     (*gro_complete)(struct sock *sk,
                                              struct sk_buff *skb,
                                              int nhoff);
+     /* Flow dissector function for a UDP socket */
+     enum flow_dissect_ret (*flow_dissect)(struct sock *sk,
+                     const struct sk_buff *skb,
+                     struct flow_dissector_key_control *key_control,
+                     struct flow_dissector *flow_dissector,
+                     void *target_container, void *data,
+                     __be16 *p_proto, u8 *p_ip_proto, int *p_nhoff,
+                     int *p_hlen, unsigned int flags);

      /* udp_recvmsg try to use this before splicing sk_receive_queue */
      struct sk_buff_head     reader_queue ____cacheline_aligned_in_smp;

diff --git a/include/net/udp.h b/include/net/udp.h
index f3d1de6f0983..499e4faf8b14 100644
--- a/include/net/udp.h
+++ b/include/net/udp.h

@@ -174,6 +174,14 @@ struct sk_buff **udp_gro_receive(struct sk_buff **head, struct sk_buff *skb,
                               struct udphdr *uh, udp_lookup_t lookup);
 int udp_gro_complete(struct sk_buff *skb, int nhoff, udp_lookup_t lookup);

+enum flow_dissect_ret udp_flow_dissect(const struct sk_buff *skb,
+                     udp_lookup_t lookup,
+                     struct flow_dissector_key_control *key_control,
+                     struct flow_dissector *flow_dissector,
+                     void *target_container, void *data,
+                     __be16 *p_proto, u8 *p_ip_proto, int *p_nhoff,
+                     int *p_hlen, unsigned int flags);
+
 static inline struct udphdr *udp_gro_udphdr(struct sk_buff *skb)
 {
      struct udphdr *uh;

diff --git a/include/net/udp_tunnel.h b/include/net/udp_tunnel.h
index 10cce0dd4450..b7102e0f41a9 100644
--- a/include/net/udp_tunnel.h
+++ b/include/net/udp_tunnel.h

@@ -69,6 +69,13 @@ typedef struct sk_buff **(*udp_tunnel_gro_receive_t)(struct sock *sk,
                                                   struct sk_buff *skb);
 typedef int (*udp_tunnel_gro_complete_t)(struct sock *sk, struct sk_buff *skb,
                                       int nhoff);
+typedef enum flow_dissect_ret (*udp_tunnel_flow_dissect_t)(struct sock *sk,
+                     const struct sk_buff *skb,
+                     struct flow_dissector_key_control *key_control,
+                     struct flow_dissector *flow_dissector,
+                     void *target_container, void *data,
+                     __be16 *p_proto, u8 *p_ip_proto, int *p_nhoff,
+                     int *p_hlen, unsigned int flags);

 struct udp_tunnel_sock_cfg {
      void *sk_user_data;     /* user data used by encap_rcv call back */

@@ -78,6 +85,7 @@ struct udp_tunnel_sock_cfg {
      udp_tunnel_encap_destroy_t encap_destroy;
      udp_tunnel_gro_receive_t gro_receive;
      udp_tunnel_gro_complete_t gro_complete;
+     udp_tunnel_flow_dissect_t flow_dissect;
 };

 /* Setup the given (UDP) sock to receive UDP encapsulated packets */

diff --git a/net/ipv4/udp_offload.c b/net/ipv4/udp_offload.c
index 97658bfc1b58..7f0a7ed4a6f7 100644
--- a/net/ipv4/udp_offload.c
+++ b/net/ipv4/udp_offload.c

@@ -328,11 +328,56 @@ static int udp4_gro_complete(struct sk_buff *skb, int nhoff)
      return udp_gro_complete(skb, nhoff, udp4_lib_lookup_skb);
 }

+enum flow_dissect_ret udp_flow_dissect(const struct sk_buff *skb,
+                     udp_lookup_t lookup,
+                     struct flow_dissector_key_control *key_control,
+                     struct flow_dissector *flow_dissector,
+                     void *target_container, void *data,
+                     __be16 *p_proto, u8 *p_ip_proto, int *p_nhoff,
+                     int *p_hlen, unsigned int flags)
+{
+     enum flow_dissect_ret ret = FLOW_DISSECT_RET_CONTINUE;
+     struct udphdr *uh, _uh;
+     struct sock *sk;
+
+     uh = __skb_header_pointer(skb, *p_nhoff, sizeof(_uh), data,
+                               *p_hlen, &_uh);
+     if (!uh)
+             return FLOW_DISSECT_RET_OUT_BAD;
+
+     rcu_read_lock();
+
+     sk = (*lookup)(skb, uh->source, uh->dest);
+
+     if (sk && udp_sk(sk)->flow_dissect)
+             ret = udp_sk(sk)->flow_dissect(sk, skb, key_control,
+                                            flow_dissector, target_container,
+                                            data, p_proto, p_ip_proto,
+                                            p_nhoff, p_hlen, flags);
+     rcu_read_unlock();
+
+     return ret;
+}
+EXPORT_SYMBOL(udp_flow_dissect);

If I read the above correctly, this is going to add another full UDP
lookup per UDP packet, can we avoid it with some static key enabled by
vxlan/fou/etc. ?

That would also limit the exposure if a bug is discovered. The
vulnerability of this critical path also came up with the recent
flow dissector expansion for ipv6 neighbor discovery.

  http://patchwork.ozlabs.org/patch/722957/

Ideally, flow dissector support for less common protocols can be
disabled administratively.

That said, the parser code looks great to me.