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, 26 insertions, 4 deletions

diff --git a/samples/bpf/xdp_adjust_tail_user.c b/samples/bpf/xdp_adjust_tail_user.c
index 049bddf7778b..07e1b9269e49 100644
--- a/samples/bpf/xdp_adjust_tail_user.c
+++ b/samples/bpf/xdp_adjust_tail_user.c
@@ -25,11 +25,24 @@
 
 static int ifindex = -1;
 static __u32 xdp_flags = XDP_FLAGS_UPDATE_IF_NOEXIST;
+static __u32 prog_id;
 
 static void int_exit(int sig)
 {
-	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(1);
+		}
+		if (prog_id == curr_prog_id)
+			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(0);
 }
 
@@ -72,11 +85,14 @@ int main(int argc, char **argv)
 	};
 	unsigned char opt_flags[256] = {};
 	const char *optstr = "i:T:SNFh";
+	struct bpf_prog_info info = {};
+	__u32 info_len = sizeof(info);
 	unsigned int kill_after_s = 0;
 	int i, prog_fd, map_fd, opt;
 	struct bpf_object *obj;
 	struct bpf_map *map;
 	char filename[256];
+	int err;
 
 	for (i = 0; i < strlen(optstr); i++)
 		if (optstr[i] != 'h' && 'a' <= optstr[i] && optstr[i] <= 'z')
@@ -146,9 +162,15 @@ int main(int argc, char **argv)
 		return 1;
 	}
 
-	poll_stats(map_fd, kill_after_s);
+	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 1;
+	}
+	prog_id = info.id;
 
-	bpf_set_link_xdp_fd(ifindex, -1, xdp_flags);
+	poll_stats(map_fd, kill_after_s);
+	int_exit(0);
 
 	return 0;
 }