bpf: sockmap, synchronize_rcu before free'ing map

bpf: sockmap, synchronize_rcu before free'ing map

[ Upstream commit 2bb90e5cc90e1d09f631aeab041a9cf913a5bbe5 ]

We need to have a synchronize_rcu before free'ing the sockmap because
any outstanding psock references will have a pointer to the map and
when they use this could trigger a use after free.

Fixes: 604326b41a6fb ("bpf, sockmap: convert to generic sk_msg interface")
Signed-off-by: John Fastabend <john.fastabend@gmail.com>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Signed-off-by: Sasha Levin <sashal@kernel.org>