bpf: sockmap, add sample option to test apply_bytes helper

This adds an option to test the apply_bytes helper. This option lets
the user specify an int on the command line specifying how much data
each verdict should apply to.

When this is set a map entry is set with the bytes input by the user
and then the specified program --txmsg or --txmsg_redir will use the
value and set the applied data. If no other option is set then a
default --txmsg_apply program is run. This program will drop pkts
if an error is detected on the bytes map lookup. Useful to verify
the map lookup and apply helper are working and causing a hard
error if it is not.

Signed-off-by: John Fastabend <john.fastabend@gmail.com>
Acked-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>

samples/sockmap/sockmap_kern.c

@@ -57,6 +57,13 @@ struct bpf_map_def SEC("maps") sock_map_redir = {
 	.max_entries = 1,
 };
 
+struct bpf_map_def SEC("maps") sock_apply_bytes = {
+	.type = BPF_MAP_TYPE_ARRAY,
+	.key_size = sizeof(int),
+	.value_size = sizeof(int),
+	.max_entries = 1
+};
+
 SEC("sk_skb1")
 int bpf_prog1(struct __sk_buff *skb)
 {
@@ -123,6 +130,11 @@ int bpf_sockmap(struct bpf_sock_ops *skops)
 SEC("sk_msg1")
 int bpf_prog4(struct sk_msg_md *msg)
 {
+	int *bytes, zero = 0;
+
+	bytes = bpf_map_lookup_elem(&sock_apply_bytes, &zero);
+	if (bytes)
+		bpf_msg_apply_bytes(msg, *bytes);
 	return SK_PASS;
 }
 
@@ -131,8 +143,13 @@ int bpf_prog5(struct sk_msg_md *msg)
 {
 	void *data_end = (void *)(long) msg->data_end;
 	void *data = (void *)(long) msg->data;
+	int *bytes, err = 0, zero = 0;
 
-	bpf_printk("sk_msg2: data length %i\n", (__u32)data_end - (__u32)data);
+	bytes = bpf_map_lookup_elem(&sock_apply_bytes, &zero);
+	if (bytes)
+		err = bpf_msg_apply_bytes(msg, *bytes);
+	bpf_printk("sk_msg2: data length %i err %i\n",
+		   (__u64)data_end - (__u64)data, err);
 	return SK_PASS;
 }
 
@@ -141,9 +158,12 @@ int bpf_prog6(struct sk_msg_md *msg)
 {
 	void *data_end = (void *)(long) msg->data_end;
 	void *data = (void *)(long) msg->data;
-	int ret = 0;
+	int *bytes, zero = 0;
 
-	return bpf_msg_redirect_map(msg, &sock_map_redir, ret, 0);
+	bytes = bpf_map_lookup_elem(&sock_apply_bytes, &zero);
+	if (bytes)
+		bpf_msg_apply_bytes(msg, *bytes);
+	return bpf_msg_redirect_map(msg, &sock_map_redir, zero, 0);
 }
 
 SEC("sk_msg4")
@@ -151,10 +171,32 @@ int bpf_prog7(struct sk_msg_md *msg)
 {
 	void *data_end = (void *)(long) msg->data_end;
 	void *data = (void *)(long) msg->data;
-	int ret = 0;
+	int *bytes, err = 0, zero = 0;
 
-	bpf_printk("sk_msg3: redirect(%iB)\n", (__u32)data_end - (__u32)data);
-	return bpf_msg_redirect_map(msg, &sock_map_redir, ret, 0);
+	bytes = bpf_map_lookup_elem(&sock_apply_bytes, &zero);
+	if (bytes)
+		err = bpf_msg_apply_bytes(msg, *bytes);
+	bpf_printk("sk_msg3: redirect(%iB) err=%i\n",
+		   (__u64)data_end - (__u64)data, err);
+	return bpf_msg_redirect_map(msg, &sock_map_redir, zero, 0);
+}
+
+SEC("sk_msg5")
+int bpf_prog8(struct sk_msg_md *msg)
+{
+	void *data_end = (void *)(long) msg->data_end;
+	void *data = (void *)(long) msg->data;
+	int ret = 0, *bytes, zero = 0;
+
+	bytes = bpf_map_lookup_elem(&sock_apply_bytes, &zero);
+	if (bytes) {
+		ret = bpf_msg_apply_bytes(msg, *bytes);
+		if (ret)
+			return SK_DROP;
+	} else {
+		return SK_DROP;
+	}
+	return SK_PASS;
 }
 
 char _license[] SEC("license") = "GPL";

samples/sockmap/sockmap_user.c

@@ -59,6 +59,7 @@ int txmsg_pass;
 int txmsg_noisy;
 int txmsg_redir;
 int txmsg_redir_noisy;
+int txmsg_apply;
 
 static const struct option long_options[] = {
 	{"help",	no_argument,		NULL, 'h' },
@@ -73,6 +74,7 @@ static const struct option long_options[] = {
 	{"txmsg_noisy",		no_argument,	&txmsg_noisy, 1  },
 	{"txmsg_redir",		no_argument,	&txmsg_redir, 1  },
 	{"txmsg_redir_noisy",	no_argument,	&txmsg_redir_noisy, 1},
+	{"txmsg_apply",	required_argument,	NULL, 'a'},
 	{0, 0, NULL, 0 }
 };
 
@@ -546,7 +548,9 @@ int main(int argc, char **argv)
 	while ((opt = getopt_long(argc, argv, ":dhvc:r:i:l:t:",
 				  long_options, &longindex)) != -1) {
 		switch (opt) {
-		/* Cgroup configuration */
+		case 'a':
+			txmsg_apply = atoi(optarg);
+			break;
 		case 'c':
 			cg_fd = open(optarg, O_DIRECTORY, O_RDONLY);
 			if (cg_fd < 0) {
@@ -665,6 +669,8 @@ run:
 		tx_prog_fd = prog_fd[5];
 	else if (txmsg_redir_noisy)
 		tx_prog_fd = prog_fd[6];
+	else if (txmsg_apply)
+		tx_prog_fd = prog_fd[7];
 	else
 		tx_prog_fd = 0;
 
@@ -699,6 +705,17 @@ run:
 				err, strerror(errno));
 			return err;
 		}
+
+		if (txmsg_apply) {
+			err = bpf_map_update_elem(map_fd[3],
+						  &i, &txmsg_apply, BPF_ANY);
+			if (err) {
+				fprintf(stderr,
+					"ERROR: bpf_map_update_elem (apply_bytes):  %d (%s\n",
+					err, strerror(errno));
+				return err;
+			}
+		}
 	}
 	if (test == PING_PONG)
 		err = forever_ping_pong(rate, &options);

tools/testing/selftests/bpf/bpf_helpers.h

@@ -88,7 +88,8 @@ static int (*bpf_override_return)(void *ctx, unsigned long rc) =
 	(void *) BPF_FUNC_override_return;
 static int (*bpf_msg_redirect_map)(void *ctx, void *map, int key, int flags) =
 	(void *) BPF_FUNC_msg_redirect_map;
-
+static int (*bpf_msg_apply_bytes)(void *ctx, int len) =
+	(void *) BPF_FUNC_msg_apply_bytes;
 
 /* llvm builtin functions that eBPF C program may use to
  * emit BPF_LD_ABS and BPF_LD_IND instructions