selftests/bpf: add sockopt test that exercises sk helpers

socktop test that introduces new SOL_CUSTOM sockopt level and
stores whatever users sets in sk storage. Whenever getsockopt
is called, the original value is retrieved.

v9:
* SO_SNDBUF example to override user-supplied buffer

v7:
* use retval=0 and optlen-1

v6:
* test 'ret=1' use-case as well (Alexei Starovoitov)

v4:
* don't call bpf_sk_fullsock helper

v3:
* drop (__u8 *)(long) casts for optval{,_end}

v2:
* new test

Cc: Andrii Nakryiko <andriin@fb.com>
Cc: Martin Lau <kafai@fb.com>
Signed-off-by: Stanislav Fomichev <sdf@google.com>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>

1 files changed, 111 insertions, 0 deletions

diff --git a/tools/testing/selftests/bpf/progs/sockopt_sk.c b/tools/testing/selftests/bpf/progs/sockopt_sk.c
new file mode 100644
index 000000000000..076122c898e9
--- /dev/null
+++ b/tools/testing/selftests/bpf/progs/sockopt_sk.c
@@ -0,0 +1,111 @@
+// SPDX-License-Identifier: GPL-2.0
+#include <netinet/in.h>
+#include <linux/bpf.h>
+#include "bpf_helpers.h"
+
+char _license[] SEC("license") = "GPL";
+__u32 _version SEC("version") = 1;
+
+#define SOL_CUSTOM			0xdeadbeef
+
+struct sockopt_sk {
+	__u8 val;
+};
+
+struct bpf_map_def SEC("maps") socket_storage_map = {
+	.type = BPF_MAP_TYPE_SK_STORAGE,
+	.key_size = sizeof(int),
+	.value_size = sizeof(struct sockopt_sk),
+	.map_flags = BPF_F_NO_PREALLOC,
+};
+BPF_ANNOTATE_KV_PAIR(socket_storage_map, int, struct sockopt_sk);
+
+SEC("cgroup/getsockopt")
+int _getsockopt(struct bpf_sockopt *ctx)
+{
+	__u8 *optval_end = ctx->optval_end;
+	__u8 *optval = ctx->optval;
+	struct sockopt_sk *storage;
+
+	if (ctx->level == SOL_IP && ctx->optname == IP_TOS)
+		/* Not interested in SOL_IP:IP_TOS;
+		 * let next BPF program in the cgroup chain or kernel
+		 * handle it.
+		 */
+		return 1;
+
+	if (ctx->level == SOL_SOCKET && ctx->optname == SO_SNDBUF) {
+		/* Not interested in SOL_SOCKET:SO_SNDBUF;
+		 * let next BPF program in the cgroup chain or kernel
+		 * handle it.
+		 */
+		return 1;
+	}
+
+	if (ctx->level != SOL_CUSTOM)
+		return 0; /* EPERM, deny everything except custom level */
+
+	if (optval + 1 > optval_end)
+		return 0; /* EPERM, bounds check */
+
+	storage = bpf_sk_storage_get(&socket_storage_map, ctx->sk, 0,
+				     BPF_SK_STORAGE_GET_F_CREATE);
+	if (!storage)
+		return 0; /* EPERM, couldn't get sk storage */
+
+	if (!ctx->retval)
+		return 0; /* EPERM, kernel should not have handled
+			   * SOL_CUSTOM, something is wrong!
+			   */
+	ctx->retval = 0; /* Reset system call return value to zero */
+
+	optval[0] = storage->val;
+	ctx->optlen = 1;
+
+	return 1;
+}
+
+SEC("cgroup/setsockopt")
+int _setsockopt(struct bpf_sockopt *ctx)
+{
+	__u8 *optval_end = ctx->optval_end;
+	__u8 *optval = ctx->optval;
+	struct sockopt_sk *storage;
+
+	if (ctx->level == SOL_IP && ctx->optname == IP_TOS)
+		/* Not interested in SOL_IP:IP_TOS;
+		 * let next BPF program in the cgroup chain or kernel
+		 * handle it.
+		 */
+		return 1;
+
+	if (ctx->level == SOL_SOCKET && ctx->optname == SO_SNDBUF) {
+		/* Overwrite SO_SNDBUF value */
+
+		if (optval + sizeof(__u32) > optval_end)
+			return 0; /* EPERM, bounds check */
+
+		*(__u32 *)optval = 0x55AA;
+		ctx->optlen = 4;
+
+		return 1;
+	}
+
+	if (ctx->level != SOL_CUSTOM)
+		return 0; /* EPERM, deny everything except custom level */
+
+	if (optval + 1 > optval_end)
+		return 0; /* EPERM, bounds check */
+
+	storage = bpf_sk_storage_get(&socket_storage_map, ctx->sk, 0,
+				     BPF_SK_STORAGE_GET_F_CREATE);
+	if (!storage)
+		return 0; /* EPERM, couldn't get sk storage */
+
+	storage->val = optval[0];
+	ctx->optlen = -1; /* BPF has consumed this option, don't call kernel
+			   * setsockopt handler.
+			   */
+
+	return 1;
+}