libbpf: Fix XDP program load regression for old kernels

Fix regression in libbpf, introduced by XDP link change, which causes XDP
programs to fail to be loaded into kernel due to specified BPF_XDP
expected_attach_type. While kernel doesn't enforce expected_attach_type for
BPF_PROG_TYPE_XDP, some old kernels already support XDP program, but they
don't yet recognize expected_attach_type field in bpf_attr, so setting it to
non-zero value causes program load to fail.

Luckily, libbpf already has a mechanism to deal with such cases, so just make
expected_attach_type optional for XDP programs.

Fixes: dc8698cac7aa ("libbpf: Add support for BPF XDP link")
Reported-by: Nikita Shirokov <tehnerd@tehnerd.com>
Reported-by: Udip Pant <udippant@fb.com>
Signed-off-by: Andrii Nakryiko <andriin@fb.com>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Link: https://lore.kernel.org/bpf/20200924171705.3803628-1-andriin@fb.com

diff --git a/tools/lib/bpf/libbpf.c b/tools/lib/bpf/libbpf.c
index 7253b833576c05375632b20ce6aa4960b1ee2587..e493d6048143f0cc1ed3b7bef32ee6606b556974 100644 (file)
--- a/tools/lib/bpf/libbpf.c
+++ b/tools/lib/bpf/libbpf.c
@@ -6925,7 +6925,7 @@ static const struct bpf_sec_def section_defs[] = {
                                                BPF_XDP_DEVMAP),
        BPF_EAPROG_SEC("xdp_cpumap/",           BPF_PROG_TYPE_XDP,
                                                BPF_XDP_CPUMAP),
-       BPF_EAPROG_SEC("xdp",                   BPF_PROG_TYPE_XDP,
+       BPF_APROG_SEC("xdp",                    BPF_PROG_TYPE_XDP,
                                                BPF_XDP),
        BPF_PROG_SEC("perf_event",              BPF_PROG_TYPE_PERF_EVENT),
        BPF_PROG_SEC("lwt_in",                  BPF_PROG_TYPE_LWT_IN),