tools/bpftool: Fix attaching flow dissector

My earlier patch to reject non-zero arguments to flow dissector attach
broke attaching via bpftool. Instead of 0 it uses -1 for target_fd.
Fix this by passing a zero argument when attaching the flow dissector.

Fixes: 1b514239e859 ("bpf: flow_dissector: Check value of unused flags to BPF_PROG_ATTACH")
Reported-by: Jiri Benc <jbenc@redhat.com>
Signed-off-by: Lorenz Bauer <lmb@cloudflare.com>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Acked-by: Song Liu <songliubraving@fb.com>
Link: https://lore.kernel.org/bpf/20201105115230.296657-1-lmb@cloudflare.com

diff --git a/tools/bpf/bpftool/prog.c b/tools/bpf/bpftool/prog.c
index d942c1e..acdb2c2 100644 (file)
--- a/tools/bpf/bpftool/prog.c
+++ b/tools/bpf/bpftool/prog.c
@@ -940,7 +940,7 @@ static int parse_attach_detach_args(int argc, char **argv, int *progfd,
        }
 
        if (*attach_type == BPF_FLOW_DISSECTOR) {
        }
 
        if (*attach_type == BPF_FLOW_DISSECTOR) {

-               *mapfd = -1;
+               *mapfd = 0;

                return 0;
        }
 
                return 0;
        }