libbpf: fix attach of prog with multiple sections

When BPF programs which consists of multiple executable sections via
iproute2+libbpf (configured with LIBBPF_FORCE=on), we noticed that a
wrong section can be attached to a device. E.g.:

    # tc qdisc replace dev lxc_health clsact
    # tc filter replace dev lxc_health ingress prio 1 \
        handle 1 bpf da obj bpf_lxc.o sec from-container
    # tc filter show dev lxc_health ingress filter protocol all
        pref 1 bpf chain 0 filter protocol all pref 1 bpf chain 0
        handle 0x1 bpf_lxc.o:[__send_drop_notify] <-- WRONG SECTION
        direct-action not_in_hw id 38 tag 7d891814eda6809e jited

After taking a closer look into load_bpf_object() in lib/bpf_libbpf.c,
we noticed that the filter used in the program iterator does not check
whether a program section name matches a requested section name
(cfg->section). This can lead to a wrong prog FD being used to attach
the program.

Fixes: 6d61a2b55799 ("lib: add libbpf support")
Signed-off-by: Martynas Pumputis <m@lambda.lt>
Acked-by: Hangbin Liu <haliu@redhat.com>
Signed-off-by: Stephen Hemminger <stephen@networkplumber.org>

diff --git a/lib/bpf_libbpf.c b/lib/bpf_libbpf.c
index 864f8c351b7d38e056121d93cefa0d5ce35f2563..dbec2cb560ccc0c6977d9e754bcb2f60a94d0dca 100644 (file)
--- a/lib/bpf_libbpf.c
+++ b/lib/bpf_libbpf.c
@@ -268,10 +268,12 @@ static int load_bpf_object(struct bpf_cfg_in *cfg)
        }
 
        bpf_object__for_each_program(p, obj) {
+               bool prog_to_attach = !prog && cfg->section &&
+                       !strcmp(get_bpf_program__section_name(p), cfg->section);
+
                /* Only load the programs that will either be subsequently
                 * attached or inserted into a tail call map */
-               if (find_legacy_tail_calls(p, obj) < 0 && cfg->section &&
-                   strcmp(get_bpf_program__section_name(p), cfg->section)) {
+               if (find_legacy_tail_calls(p, obj) < 0 && !prog_to_attach) {
                        ret = bpf_program__set_autoload(p, false);
                        if (ret)
                                return -EINVAL;
@@ -280,7 +282,8 @@ static int load_bpf_object(struct bpf_cfg_in *cfg)
 
                bpf_program__set_type(p, cfg->type);
                bpf_program__set_ifindex(p, cfg->ifindex);
-               if (!prog)
+
+               if (prog_to_attach)
                        prog = p;
        }