bpf: pass sk to helper functions

BPF helper functions access socket fields through skb->sk. This is not
set in ingress cgroup and socket filters. The association is only made
in skb_set_owner_r once the filter has accepted the packet. Sk is
available as socket lookup has taken place.

Temporarily set skb->sk to sk in these cases.
Signed-off-by: Willem de Bruijn <willemb@google.com>
Acked-by: Alexei Starovoitov <ast@kernel.org>
Signed-off-by: David S. Miller <davem@davemloft.net>

kernel/bpf/cgroup.c

@@ -154,7 +154,7 @@ int __cgroup_bpf_update(struct cgroup *cgrp, struct cgroup *parent,
 
 /**
  * __cgroup_bpf_run_filter_skb() - Run a program for packet filtering
- * @sk: The socken sending or receiving traffic
+ * @sk: The socket sending or receiving traffic
  * @skb: The skb that is being sent or received
  * @type: The type of program to be exectuted
  *
@@ -189,10 +189,13 @@ int __cgroup_bpf_run_filter_skb(struct sock *sk,
 	prog = rcu_dereference(cgrp->bpf.effective[type]);
 	if (prog) {
 		unsigned int offset = skb->data - skb_network_header(skb);
+		struct sock *save_sk = skb->sk;
 
+		skb->sk = sk;
 		__skb_push(skb, offset);
 		ret = bpf_prog_run_save_cb(prog, skb) == 1 ? 0 : -EPERM;
 		__skb_pull(skb, offset);
+		skb->sk = save_sk;
 	}
 
 	rcu_read_unlock();

net/core/filter.c

@@ -92,8 +92,13 @@ int sk_filter_trim_cap(struct sock *sk, struct sk_buff *skb, unsigned int cap)
 	rcu_read_lock();
 	filter = rcu_dereference(sk->sk_filter);
 	if (filter) {
-		unsigned int pkt_len = bpf_prog_run_save_cb(filter->prog, skb);
+		struct sock *save_sk = skb->sk;
+		unsigned int pkt_len;
+
+		skb->sk = sk;
+		pkt_len = bpf_prog_run_save_cb(filter->prog, skb);
 		err = pkt_len ? pskb_trim(skb, max(cap, pkt_len)) : -EPERM;
+		skb->sk = save_sk;
 	}
 	rcu_read_unlock();