UPSTREAM: bpf: Add a check for struct bpf_fib_lookup size

[ Upstream commit 59b418c7063d30e0a3e1f592d47df096db83185c ]

The struct bpf_fib_lookup should not grow outside of its 64 bytes.
Add a static assert to validate this.

Suggested-by: David Ahern <dsahern@kernel.org>
Change-Id: I65c2aaa9ae8c055a2ee11af346ee73684a9496d7
Signed-off-by: Anton Protopopov <aspsk@isovalent.com>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Link: https://lore.kernel.org/bpf/20240326101742.17421-4-aspsk@isovalent.com
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>
Signed-off-by: Naveen <133593113+elohim-etz@users.noreply.github.com>

Author: aspsk

net/core/filter.c

@@ -81,6 +81,9 @@
 #include <linux/btf_ids.h>
 #include <net/tls.h>
 
+/* Keep the struct bpf_fib_lookup small so that it fits into a cacheline */
+static_assert(sizeof(struct bpf_fib_lookup) == 64, "struct bpf_fib_lookup size check");
+
 static const struct bpf_func_proto *
 bpf_sk_base_func_proto(enum bpf_func_id func_id);