selftests/bpf: Add test for SO_BINDTODEVICE opt of bpf_setsockopt

This test intended to verify if SO_BINDTODEVICE option works in
bpf_setsockopt. Because we already in the SOL_SOCKET level in this
connect bpf prog its safe to verify the sanity in the beginning of
the connect_v4_prog by calling the bind_to_device test helper.

The testing environment already created by the test_sock_addr.sh
script so this test assume that two netdevices already existing in
the system: veth pair with names test_sock_addr1 and test_sock_addr2.
The test will try to bind the socket to those devices first.
Then the test assume there are no netdevice with "nonexistent_dev"
name so the bpf_setsockopt will give use ENODEV error.
At the end the test remove the device binding from the socket
by binding it to an empty name.
Signed-off-by: Ferenc Fejes <fejes@inf.elte.hu>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Link: https://lore.kernel.org/bpf/3f055b8e45c65639c5c73d0b4b6c589e60b86f15.1590871065.git.fejes@inf.elte.hu

tools/testing/selftests/bpf/progs/connect4_prog.c

@@ -9,6 +9,8 @@
 #include <linux/in6.h>
 #include <sys/socket.h>
 #include <netinet/tcp.h>
+#include <linux/if.h>
+#include <errno.h>
 
 #include <bpf/bpf_helpers.h>
 #include <bpf/bpf_endian.h>
@@ -21,6 +23,10 @@
 #define TCP_CA_NAME_MAX 16
 #endif
 
+#ifndef IFNAMSIZ
+#define IFNAMSIZ 16
+#endif
+
 int _version SEC("version") = 1;
 
 __attribute__ ((noinline))
@@ -75,6 +81,29 @@ static __inline int set_cc(struct bpf_sock_addr *ctx)
 	return 0;
 }
 
+static __inline int bind_to_device(struct bpf_sock_addr *ctx)
+{
+	char veth1[IFNAMSIZ] = "test_sock_addr1";
+	char veth2[IFNAMSIZ] = "test_sock_addr2";
+	char missing[IFNAMSIZ] = "nonexistent_dev";
+	char del_bind[IFNAMSIZ] = "";
+
+	if (bpf_setsockopt(ctx, SOL_SOCKET, SO_BINDTODEVICE,
+				&veth1, sizeof(veth1)))
+		return 1;
+	if (bpf_setsockopt(ctx, SOL_SOCKET, SO_BINDTODEVICE,
+				&veth2, sizeof(veth2)))
+		return 1;
+	if (bpf_setsockopt(ctx, SOL_SOCKET, SO_BINDTODEVICE,
+				&missing, sizeof(missing)) != -ENODEV)
+		return 1;
+	if (bpf_setsockopt(ctx, SOL_SOCKET, SO_BINDTODEVICE,
+				&del_bind, sizeof(del_bind)))
+		return 1;
+
+	return 0;
+}
+
 SEC("cgroup/connect4")
 int connect_v4_prog(struct bpf_sock_addr *ctx)
 {
@@ -88,6 +117,10 @@ int connect_v4_prog(struct bpf_sock_addr *ctx)
 	tuple.ipv4.daddr = bpf_htonl(DST_REWRITE_IP4);
 	tuple.ipv4.dport = bpf_htons(DST_REWRITE_PORT4);
 
+	/* Bind to device and unbind it. */
+	if (bind_to_device(ctx))
+		return 0;
+
 	if (ctx->type != SOCK_STREAM && ctx->type != SOCK_DGRAM)
 		return 0;
 	else if (ctx->type == SOCK_STREAM)