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, 34 insertions, 17 deletions

diff --git a/samples/bpf/xdp_router_ipv4_user.c b/samples/bpf/xdp_router_ipv4_user.c
index 208d6a996478..79fe7bc26ab4 100644
--- a/samples/bpf/xdp_router_ipv4_user.c
+++ b/samples/bpf/xdp_router_ipv4_user.c
@@ -30,7 +30,8 @@
 
 int sock, sock_arp, flags = XDP_FLAGS_UPDATE_IF_NOEXIST;
 static int total_ifindex;
-int *ifindex_list;
+static int *ifindex_list;
+static __u32 *prog_id_list;
 char buf[8192];
 static int lpm_map_fd;
 static int rxcnt_map_fd;
@@ -41,23 +42,34 @@ static int tx_port_map_fd;
 static int get_route_table(int rtm_family);
 static void int_exit(int sig)
 {
+	__u32 prog_id = 0;
 	int i = 0;
 
-	for (i = 0; i < total_ifindex; i++)
-		bpf_set_link_xdp_fd(ifindex_list[i], -1, flags);
+	for (i = 0; i < total_ifindex; i++) {
+		if (bpf_get_link_xdp_id(ifindex_list[i], &prog_id, flags)) {
+			printf("bpf_get_link_xdp_id on iface %d failed\n",
+			       ifindex_list[i]);
+			exit(1);
+		}
+		if (prog_id_list[i] == prog_id)
+			bpf_set_link_xdp_fd(ifindex_list[i], -1, flags);
+		else if (!prog_id)
+			printf("couldn't find a prog id on iface %d\n",
+			       ifindex_list[i]);
+		else
+			printf("program on iface %d changed, not removing\n",
+			       ifindex_list[i]);
+		prog_id = 0;
+	}
 	exit(0);
 }
 
 static void close_and_exit(int sig)
 {
-	int i = 0;
-
 	close(sock);
 	close(sock_arp);
 
-	for (i = 0; i < total_ifindex; i++)
-		bpf_set_link_xdp_fd(ifindex_list[i], -1, flags);
-	exit(0);
+	int_exit(0);
 }
 
 /* Get the mac address of the interface given interface name */
@@ -186,13 +198,8 @@ static void read_route(struct nlmsghdr *nh, int nll)
 		route.iface_name = alloca(sizeof(char *) * IFNAMSIZ);
 		route.iface_name = if_indextoname(route.iface, route.iface_name);
 		route.mac = getmac(route.iface_name);
-		if (route.mac == -1) {
-			int i = 0;
-
-			for (i = 0; i < total_ifindex; i++)
-				bpf_set_link_xdp_fd(ifindex_list[i], -1, flags);
-			exit(0);
-		}
+		if (route.mac == -1)
+			int_exit(0);
 		assert(bpf_map_update_elem(tx_port_map_fd,
 					   &route.iface, &route.iface, 0) == 0);
 		if (rtm_family == AF_INET) {
@@ -625,12 +632,14 @@ int main(int ac, 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);
 	const char *optstr = "SF";
 	struct bpf_object *obj;
 	char filename[256];
 	char **ifname_list;
 	int prog_fd, opt;
-	int i = 1;
+	int err, i = 1;
 
 	snprintf(filename, sizeof(filename), "%s_kern.o", argv[0]);
 	prog_load_attr.file = filename;
@@ -687,7 +696,7 @@ int main(int ac, char **argv)
 		return 1;
 	}
 
-	ifindex_list = (int *)malloc(total_ifindex * sizeof(int *));
+	ifindex_list = (int *)calloc(total_ifindex, sizeof(int *));
 	for (i = 0; i < total_ifindex; i++) {
 		ifindex_list[i] = if_nametoindex(ifname_list[i]);
 		if (!ifindex_list[i]) {
@@ -696,6 +705,7 @@ int main(int ac, char **argv)
 			return 1;
 		}
 	}
+	prog_id_list = (__u32 *)calloc(total_ifindex, sizeof(__u32 *));
 	for (i = 0; i < total_ifindex; i++) {
 		if (bpf_set_link_xdp_fd(ifindex_list[i], prog_fd, flags) < 0) {
 			printf("link set xdp fd failed\n");
@@ -706,6 +716,13 @@ int main(int ac, char **argv)
 
 			return 1;
 		}
+		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_list[i] = info.id;
+		memset(&info, 0, sizeof(info));
 		printf("Attached to %d\n", ifindex_list[i]);
 	}
 	signal(SIGINT, int_exit);