[PATCH iproute2] libbpf: fix attach of prog with multiple sections

[Martynas Pumputis <m@lambda.lt>]

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>
---
 lib/bpf_libbpf.c | 9 ++++++---
 1 file changed, 6 insertions(+), 3 deletions(-)

diff --git a/lib/bpf_libbpf.c b/lib/bpf_libbpf.c
index d05737a4..f76b90d2 100644
--- a/lib/bpf_libbpf.c
+++ b/lib/bpf_libbpf.c
@@ -267,10 +267,12 @@ 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;
@@ -279,7 +281,8 @@ 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;
 	}
 
-- 
2.32.0