bpf: flow_dissector: Check value of unused flags to BPF_PROG_ATTACH

Using BPF_PROG_ATTACH on a flow dissector program supports neither
target_fd, attach_flags or replace_bpf_fd but accepts any value.

Enforce that all of them are zero. This is fine for replace_bpf_fd
since its presence is indicated by BPF_F_REPLACE. It's more
problematic for target_fd, since zero is a valid fd. Should we
want to use the flag later on we'd have to add an exception for
fd 0. The alternative is to force a value like -1. This requires
more changes to tests. There is also precedent for using 0,
since bpf_iter uses this for target_fd as well.

Fixes: b27f7bb590ba ("flow_dissector: Move out netns_bpf prog callbacks")
Signed-off-by: Lorenz Bauer <lmb@cloudflare.com>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Link: https://lore.kernel.org/bpf/20200629095630.7933-2-lmb@cloudflare.com

diff --git a/kernel/bpf/net_namespace.c b/kernel/bpf/net_namespace.c
index 7a34a8c..03045f4 100644 (file)
--- a/kernel/bpf/net_namespace.c
+++ b/kernel/bpf/net_namespace.c
@@ -209,6 +209,9 @@ int netns_bpf_prog_attach(const union bpf_attr *attr, struct bpf_prog *prog)
        struct net *net;
        int ret;
 
+       if (attr->target_fd || attr->attach_flags || attr->replace_bpf_fd)
+               return -EINVAL;
+
        type = to_netns_bpf_attach_type(attr->attach_type);
        if (type < 0)
                return -EINVAL;