selftest: bpf: Test copying a sockmap and sockhash

Since we can now call map_update_elem(sockmap) from bpf_iter context it's possible to copy a sockmap or sockhash in the kernel. Add a selftest which exercises this. Signed-off-by: Lorenz Bauer <lmb@cloudflare.com> Signed-off-by: Alexei Starovoitov <ast@kernel.org> Link: https://lore.kernel.org/bpf/20200928090805.23343-5-lmb@cloudflare.com

Author: lmb

tools/testing/selftests/bpf/prog_tests/sockmap_basic.c

@@ -194,7 +194,7 @@ static void test_sockmap_invalid_update(void)
 test_sockmap_invalid_update__destroy(skel);
 }
 
-static void test_sockmap_iter(enum bpf_map_type map_type)
+static void test_sockmap_copy(enum bpf_map_type map_type)
 {
 DECLARE_LIBBPF_OPTS(bpf_iter_attach_opts, opts);
 int err, len, src_fd, iter_fd, duration = 0;
@@ -242,7 +242,7 @@ static void test_sockmap_iter(enum bpf_map_type map_type)
 linfo.map.map_fd = src_fd;
 opts.link_info = &linfo;
 opts.link_info_len = sizeof(linfo);
-link = bpf_program__attach_iter(skel->progs.count_elems, &opts);
+link = bpf_program__attach_iter(skel->progs.copy, &opts);
 if (CHECK(IS_ERR(link), "attach_iter", "attach_iter failed\n"))
 goto out;
 
@@ -265,6 +265,8 @@ static void test_sockmap_iter(enum bpf_map_type map_type)
  skel->bss->socks, num_sockets))
 goto close_iter;
 
+compare_cookies(src, skel->maps.dst);
+
 close_iter:
 close(iter_fd);
 free_link:
@@ -294,8 +296,8 @@ void test_sockmap_basic(void)
 test_sockmap_update(BPF_MAP_TYPE_SOCKHASH);
 if (test__start_subtest("sockmap update in unsafe context"))
 test_sockmap_invalid_update();
-if (test__start_subtest("sockmap iter"))
-test_sockmap_iter(BPF_MAP_TYPE_SOCKMAP);
-if (test__start_subtest("sockhash iter"))
-test_sockmap_iter(BPF_MAP_TYPE_SOCKHASH);
+if (test__start_subtest("sockmap copy"))
+test_sockmap_copy(BPF_MAP_TYPE_SOCKMAP);
+if (test__start_subtest("sockhash copy"))
+test_sockmap_copy(BPF_MAP_TYPE_SOCKHASH);
 }

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

@@ -22,21 +22,38 @@ struct {
 __type(value, __u64);
 } sockhash SEC(".maps");
 
+struct {
+__uint(type, BPF_MAP_TYPE_SOCKHASH);
+__uint(max_entries, 64);
+__type(key, __u32);
+__type(value, __u64);
+} dst SEC(".maps");
+
 __u32 elems = 0;
 __u32 socks = 0;
 
 SEC("iter/sockmap")
-int count_elems(struct bpf_iter__sockmap *ctx)
+int copy(struct bpf_iter__sockmap *ctx)
 {
 struct sock *sk = ctx->sk;
 __u32 tmp, *key = ctx->key;
 int ret;
 
-if (key)
-elems++;
+if (!key)
+return 0;
+
+elems++;
+
+/* We need a temporary buffer on the stack, since the verifier doesn't
+ * let us use the pointer from the context as an argument to the helper.
+ */
+tmp = *key;
 
-if (sk)
+if (sk) {
 socks++;
+return bpf_map_update_elem(&dst, &tmp, sk, 0) != 0;
+}
 
-return 0;
+ret = bpf_map_delete_elem(&dst, &tmp);
+return ret && ret != -ENOENT;
 }