selftests/bpf: Selftest for sys_sendmsg hooks

Add selftest for BPF_CGROUP_UDP4_SENDMSG and BPF_CGROUP_UDP6_SENDMSG
attach types.

Try to sendmsg(2) to specific IP:port and test that:
* source IP is overridden as expected.
* remote IP:port pair is overridden as expected;

Both UDPv4 and UDPv6 are tested.

Output:
  # test_sock_addr.sh 2>/dev/null
  Wait for testing IPv4/IPv6 to become available ... OK
  ... pre-existing test-cases skipped ...
  Test case: sendmsg4: load prog with wrong expected attach type .. [PASS]
  Test case: sendmsg4: attach prog with wrong attach type .. [PASS]
  Test case: sendmsg4: rewrite IP & port (asm) .. [PASS]
  Test case: sendmsg4: rewrite IP & port (C) .. [PASS]
  Test case: sendmsg4: deny call .. [PASS]
  Test case: sendmsg6: load prog with wrong expected attach type .. [PASS]
  Test case: sendmsg6: attach prog with wrong attach type .. [PASS]
  Test case: sendmsg6: rewrite IP & port (asm) .. [PASS]
  Test case: sendmsg6: rewrite IP & port (C) .. [PASS]
  Test case: sendmsg6: IPv4-mapped IPv6 .. [PASS]
  Test case: sendmsg6: deny call .. [PASS]
  Summary: 27 PASSED, 0 FAILED

Signed-off-by: Andrey Ignatov <rdna@fb.com>
Acked-by: Alexei Starovoitov <ast@kernel.org>
Acked-by: Martin KaFai Lau <kafai@fb.com>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>

1 files changed, 49 insertions, 0 deletions

diff --git a/tools/testing/selftests/bpf/sendmsg4_prog.c b/tools/testing/selftests/bpf/sendmsg4_prog.c
new file mode 100644
index 000000000000..a91536b1c47e
--- /dev/null
+++ b/tools/testing/selftests/bpf/sendmsg4_prog.c
@@ -0,0 +1,49 @@
+// SPDX-License-Identifier: GPL-2.0
+// Copyright (c) 2018 Facebook
+
+#include <linux/stddef.h>
+#include <linux/bpf.h>
+#include <sys/socket.h>
+
+#include "bpf_helpers.h"
+#include "bpf_endian.h"
+
+#define SRC1_IP4		0xAC100001U /* 172.16.0.1 */
+#define SRC2_IP4		0x00000000U
+#define SRC_REWRITE_IP4		0x7f000004U
+#define DST_IP4			0xC0A801FEU /* 192.168.1.254 */
+#define DST_REWRITE_IP4		0x7f000001U
+#define DST_PORT		4040
+#define DST_REWRITE_PORT4	4444
+
+int _version SEC("version") = 1;
+
+SEC("cgroup/sendmsg4")
+int sendmsg_v4_prog(struct bpf_sock_addr *ctx)
+{
+	if (ctx->type != SOCK_DGRAM)
+		return 0;
+
+	/* Rewrite source. */
+	if (ctx->msg_src_ip4 == bpf_htonl(SRC1_IP4) ||
+	    ctx->msg_src_ip4 == bpf_htonl(SRC2_IP4)) {
+		ctx->msg_src_ip4 = bpf_htonl(SRC_REWRITE_IP4);
+	} else {
+		/* Unexpected source. Reject sendmsg. */
+		return 0;
+	}
+
+	/* Rewrite destination. */
+	if ((ctx->user_ip4 >> 24) == (bpf_htonl(DST_IP4) >> 24) &&
+	     ctx->user_port == bpf_htons(DST_PORT)) {
+		ctx->user_ip4 = bpf_htonl(DST_REWRITE_IP4);
+		ctx->user_port = bpf_htons(DST_REWRITE_PORT4);
+	} else {
+		/* Unexpected source. Reject sendmsg. */
+		return 0;
+	}
+
+	return 1;
+}
+
+char _license[] SEC("license") = "GPL";