Commit 34c5bd66 introduced the possibility that an
uninitialized pointer on the stack (orig_fp) can call into
sk_unattached_filter_destroy() when its value is non NULL.

Before that commit orig_fp was only destroyed in the same
block where it was assigned a valid BPF prog before. Fix it
up by initializing it to NULL.

Fixes: 34c5bd66 ("net: filter: don't release unattached filter through call_rcu()")
Signed-off-by: Daniel Borkmann <dborkman@redhat.com>
Cc: Pablo Neira <pablo@netfilter.org>
Cc: Alexei Starovoitov <ast@plumgrid.com>
Cc: Jiri Pirko <jiri@resnulli.us>
Signed-off-by: David S. Miller <davem@davemloft.net>