bpf: remove check in __cgroup_bpf_run_filter_skb

Originally, this patch removed a redundant check in
BPF_CGROUP_RUN_PROG_INET_EGRESS, as the check was already being done in
the function it called, __cgroup_bpf_run_filter_skb. For v2, it was
reccomended that I remove the check from __cgroup_bpf_run_filter_skb,
and add the checks to the other macro that calls that function,
BPF_CGROUP_RUN_PROG_INET_INGRESS.

To sum it up, checking that the socket exists and that it is a full
socket is now part of both macros BPF_CGROUP_RUN_PROG_INET_EGRESS and
BPF_CGROUP_RUN_PROG_INET_INGRESS, and it is no longer part of the
function they call, __cgroup_bpf_run_filter_skb.

v3->v4: Fixed weird merge conflict.
v2->v3: Sent to bpf-next instead of generic patch
v1->v2: Addressed feedback about where check should be removed.

Signed-off-by: Oliver Crumrine <ozlinuxc@gmail.com>
Acked-by: Stanislav Fomichev <sdf@google.com>
Link: https://lore.kernel.org/r/7lv62yiyvmj5a7eozv2iznglpkydkdfancgmbhiptrgvgan5sy@3fl3onchgdz3
Signed-off-by: Martin KaFai Lau <martin.lau@kernel.org>

Author: Oliver Crumrine

include/linux/bpf-cgroup.h

@@ -196,7 +196,8 @@ static inline bool cgroup_bpf_sock_enabled(struct sock *sk,
 ({									      \
 	int __ret = 0;							      \
 	if (cgroup_bpf_enabled(CGROUP_INET_INGRESS) &&			      \
-	    cgroup_bpf_sock_enabled(sk, CGROUP_INET_INGRESS))		      \
+	    cgroup_bpf_sock_enabled(sk, CGROUP_INET_INGRESS) && sk &&	      \
+	    sk_fullsock(sk))						      \
 		__ret = __cgroup_bpf_run_filter_skb(sk, skb,		      \
 						    CGROUP_INET_INGRESS); \
 									      \

kernel/bpf/cgroup.c

@@ -1364,9 +1364,6 @@ int __cgroup_bpf_run_filter_skb(struct sock *sk,
 	struct cgroup *cgrp;
 	int ret;
 
-	if (!sk || !sk_fullsock(sk))
-		return 0;
-
 	if (sk->sk_family != AF_INET && sk->sk_family != AF_INET6)
 		return 0;