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, 29 insertions, 5 deletions

diff --git a/samples/bpf/xdp_sample_pkts_user.c b/samples/bpf/xdp_sample_pkts_user.c
index 62f34827c775..dc66345a929a 100644
--- a/samples/bpf/xdp_sample_pkts_user.c
+++ b/samples/bpf/xdp_sample_pkts_user.c
@@ -24,25 +24,49 @@ static int pmu_fds[MAX_CPUS], if_idx;
 static struct perf_event_mmap_page *headers[MAX_CPUS];
 static char *if_name;
 static __u32 xdp_flags = XDP_FLAGS_UPDATE_IF_NOEXIST;
+static __u32 prog_id;
 
 static int do_attach(int idx, int fd, const char *name)
 {
+	struct bpf_prog_info info = {};
+	__u32 info_len = sizeof(info);
 	int err;
 
 	err = bpf_set_link_xdp_fd(idx, fd, xdp_flags);
-	if (err < 0)
+	if (err < 0) {
 		printf("ERROR: failed to attach program to %s\n", name);
+		return err;
+	}
+
+	err = bpf_obj_get_info_by_fd(fd, &info, &info_len);
+	if (err) {
+		printf("can't get prog info - %s\n", strerror(errno));
+		return err;
+	}
+	prog_id = info.id;
 
 	return err;
 }
 
 static int do_detach(int idx, const char *name)
 {
-	int err;
+	__u32 curr_prog_id = 0;
+	int err = 0;
 
-	err = bpf_set_link_xdp_fd(idx, -1, 0);
-	if (err < 0)
-		printf("ERROR: failed to detach program from %s\n", name);
+	err = bpf_get_link_xdp_id(idx, &curr_prog_id, 0);
+	if (err) {
+		printf("bpf_get_link_xdp_id failed\n");
+		return err;
+	}
+	if (prog_id == curr_prog_id) {
+		err = bpf_set_link_xdp_fd(idx, -1, 0);
+		if (err < 0)
+			printf("ERROR: failed to detach prog from %s\n", name);
+	} else if (!curr_prog_id) {
+		printf("couldn't find a prog id on a %s\n", name);
+	} else {
+		printf("program on interface changed, not removing\n");
+	}
 
 	return err;
 }