[PATCH bpf-next v3 4/4] selftest: bpf: Test copying a sockmap and sockhash

[Lorenz Bauer]

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 <l...@cloudflare.com>
---
 .../selftests/bpf/prog_tests/sockmap_basic.c  | 14 +++++-----
 .../selftests/bpf/progs/bpf_iter_sockmap.c    | 27 +++++++++++++++----
 2 files changed, 30 insertions(+), 11 deletions(-)

diff --git a/tools/testing/selftests/bpf/prog_tests/sockmap_basic.c 
b/tools/testing/selftests/bpf/prog_tests/sockmap_basic.c
index 316c4e271b36..4c4224e3e10a 100644
--- a/tools/testing/selftests/bpf/prog_tests/sockmap_basic.c
+++ b/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);
 }
diff --git a/tools/testing/selftests/bpf/progs/bpf_iter_sockmap.c 
b/tools/testing/selftests/bpf/progs/bpf_iter_sockmap.c
index 1af7555f6057..f3af0e30cead 100644
--- a/tools/testing/selftests/bpf/progs/bpf_iter_sockmap.c
+++ b/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;
 
-       if (sk)
+       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) {
                socks++;
+               return bpf_map_update_elem(&dst, &tmp, sk, 0) != 0;
+       }
 
-       return 0;
+       ret = bpf_map_delete_elem(&dst, &tmp);
+       return ret && ret != -ENOENT;
 }
-- 
2.25.1