samples/bpf: Check the prog id before exiting

Check the program id within the signal handler on polling xdp samples
that were previously converted to libbpf usage. Avoid the situation of
unloading the program that was not attached by sample that is exiting.
Handle also the case where bpf_get_link_xdp_id didn't exit with an error
but the xdp program was not found on an interface.

Reported-by: Michal Papaj <michal.papaj@intel.com>
Reported-by: Jakub Spizewski <jakub.spizewski@intel.com>
Signed-off-by: Maciej Fijalkowski <maciej.fijalkowski@intel.com>
Reviewed-by: Jakub Kicinski <jakub.kicinski@netronome.com>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>

1 files changed, 28 insertions, 5 deletions

diff --git a/samples/bpf/xdp_rxq_info_user.c b/samples/bpf/xdp_rxq_info_user.c
index e7a98c2a440f..1210f3b170f0 100644
--- a/samples/bpf/xdp_rxq_info_user.c
+++ b/samples/bpf/xdp_rxq_info_user.c
@@ -29,6 +29,7 @@ static const char *__doc__ = " XDP RX-queue info extract example\n\n"
 static int ifindex = -1;
 static char ifname_buf[IF_NAMESIZE];
 static char *ifname;
+static __u32 prog_id;
 
 static __u32 xdp_flags = XDP_FLAGS_UPDATE_IF_NOEXIST;
 
@@ -58,11 +59,24 @@ static const struct option long_options[] = {
 
 static void int_exit(int sig)
 {
-	fprintf(stderr,
-		"Interrupted: Removing XDP program on ifindex:%d device:%s\n",
-		ifindex, ifname);
-	if (ifindex > -1)
-		bpf_set_link_xdp_fd(ifindex, -1, xdp_flags);
+	__u32 curr_prog_id = 0;
+
+	if (ifindex > -1) {
+		if (bpf_get_link_xdp_id(ifindex, &curr_prog_id, xdp_flags)) {
+			printf("bpf_get_link_xdp_id failed\n");
+			exit(EXIT_FAIL);
+		}
+		if (prog_id == curr_prog_id) {
+			fprintf(stderr,
+				"Interrupted: Removing XDP program on ifindex:%d device:%s\n",
+				ifindex, ifname);
+			bpf_set_link_xdp_fd(ifindex, -1, xdp_flags);
+		} else if (!curr_prog_id) {
+			printf("couldn't find a prog id on a given iface\n");
+		} else {
+			printf("program on interface changed, not removing\n");
+		}
+	}
 	exit(EXIT_OK);
 }
 
@@ -447,6 +461,8 @@ int main(int argc, char **argv)
 	struct bpf_prog_load_attr prog_load_attr = {
 		.prog_type	= BPF_PROG_TYPE_XDP,
 	};
+	struct bpf_prog_info info = {};
+	__u32 info_len = sizeof(info);
 	int prog_fd, map_fd, opt, err;
 	bool use_separators = true;
 	struct config cfg = { 0 };
@@ -580,6 +596,13 @@ int main(int argc, char **argv)
 		return EXIT_FAIL_XDP;
 	}
 
+	err = bpf_obj_get_info_by_fd(prog_fd, &info, &info_len);
+	if (err) {
+		printf("can't get prog info - %s\n", strerror(errno));
+		return err;
+	}
+	prog_id = info.id;
+
 	stats_poll(interval, action, cfg_options);
 	return EXIT_OK;
 }