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, 46 insertions, 3 deletions

diff --git a/samples/bpf/xdp_redirect_map_user.c b/samples/bpf/xdp_redirect_map_user.c
index 470e1a7e8810..327226be5a06 100644
--- a/samples/bpf/xdp_redirect_map_user.c
+++ b/samples/bpf/xdp_redirect_map_user.c
@@ -29,15 +29,41 @@
 static int ifindex_in;
 static int ifindex_out;
 static bool ifindex_out_xdp_dummy_attached = true;
+static __u32 prog_id;
+static __u32 dummy_prog_id;
 
 static __u32 xdp_flags = XDP_FLAGS_UPDATE_IF_NOEXIST;
 static int rxcnt_map_fd;
 
 static void int_exit(int sig)
 {
-	bpf_set_link_xdp_fd(ifindex_in, -1, xdp_flags);
-	if (ifindex_out_xdp_dummy_attached)
-		bpf_set_link_xdp_fd(ifindex_out, -1, xdp_flags);
+	__u32 curr_prog_id = 0;
+
+	if (bpf_get_link_xdp_id(ifindex_in, &curr_prog_id, xdp_flags)) {
+		printf("bpf_get_link_xdp_id failed\n");
+		exit(1);
+	}
+	if (prog_id == curr_prog_id)
+		bpf_set_link_xdp_fd(ifindex_in, -1, xdp_flags);
+	else if (!curr_prog_id)
+		printf("couldn't find a prog id on iface IN\n");
+	else
+		printf("program on iface IN changed, not removing\n");
+
+	if (ifindex_out_xdp_dummy_attached) {
+		curr_prog_id = 0;
+		if (bpf_get_link_xdp_id(ifindex_out, &curr_prog_id,
+					xdp_flags)) {
+			printf("bpf_get_link_xdp_id failed\n");
+			exit(1);
+		}
+		if (prog_id == curr_prog_id)
+			bpf_set_link_xdp_fd(ifindex_out, -1, xdp_flags);
+		else if (!curr_prog_id)
+			printf("couldn't find a prog id on iface OUT\n");
+		else
+			printf("program on iface OUT changed, not removing\n");
+	}
 	exit(0);
 }
 
@@ -82,6 +108,8 @@ int main(int argc, char **argv)
 		.prog_type	= BPF_PROG_TYPE_XDP,
 	};
 	struct bpf_program *prog, *dummy_prog;
+	struct bpf_prog_info info = {};
+	__u32 info_len = sizeof(info);
 	int prog_fd, dummy_prog_fd;
 	const char *optstr = "FSN";
 	struct bpf_object *obj;
@@ -153,6 +181,13 @@ int main(int argc, char **argv)
 		return 1;
 	}
 
+	ret = bpf_obj_get_info_by_fd(prog_fd, &info, &info_len);
+	if (ret) {
+		printf("can't get prog info - %s\n", strerror(errno));
+		return ret;
+	}
+	prog_id = info.id;
+
 	/* Loading dummy XDP prog on out-device */
 	if (bpf_set_link_xdp_fd(ifindex_out, dummy_prog_fd,
 			    (xdp_flags | XDP_FLAGS_UPDATE_IF_NOEXIST)) < 0) {
@@ -160,6 +195,14 @@ int main(int argc, char **argv)
 		ifindex_out_xdp_dummy_attached = false;
 	}
 
+	memset(&info, 0, sizeof(info));
+	ret = bpf_obj_get_info_by_fd(dummy_prog_fd, &info, &info_len);
+	if (ret) {
+		printf("can't get prog info - %s\n", strerror(errno));
+		return ret;
+	}
+	dummy_prog_id = info.id;
+
 	signal(SIGINT, int_exit);
 	signal(SIGTERM, int_exit);