[PATCH bpf-next v4 13/13] selftests/bpf: add a test for out of bound rdonly buf access

[Yonghong Song]

If the bpf program contains out of bound access w.r.t. a
particular map key/value size, the verification will be
still okay, e.g., it will be accepted by verifier. But
it will be rejected during link_create time. A test
is added here to ensure link_create failure did happen
if out of bound access happened.
  $ ./test_progs -n 4
  ...
  #4/23 rdonly-buf-out-of-bound:OK
  ...

Signed-off-by: Yonghong Song <y...@fb.com>
---
 .../selftests/bpf/prog_tests/bpf_iter.c       | 22 ++++++++++++
 .../selftests/bpf/progs/bpf_iter_test_kern5.c | 35 +++++++++++++++++++
 2 files changed, 57 insertions(+)
 create mode 100644 tools/testing/selftests/bpf/progs/bpf_iter_test_kern5.c

diff --git a/tools/testing/selftests/bpf/prog_tests/bpf_iter.c 
b/tools/testing/selftests/bpf/prog_tests/bpf_iter.c
index ffbbeb9fa268..d95de80b1851 100644
--- a/tools/testing/selftests/bpf/prog_tests/bpf_iter.c
+++ b/tools/testing/selftests/bpf/prog_tests/bpf_iter.c
@@ -20,6 +20,7 @@
 #include "bpf_iter_bpf_array_map.skel.h"
 #include "bpf_iter_bpf_percpu_array_map.skel.h"
 #include "bpf_iter_bpf_sk_storage_map.skel.h"
+#include "bpf_iter_test_kern5.skel.h"
 
 static int duration;
 
@@ -865,6 +866,25 @@ static void test_bpf_sk_storage_map(void)
        bpf_iter_bpf_sk_storage_map__destroy(skel);
 }
 
+static void test_rdonly_buf_out_of_bound(void)
+{
+       DECLARE_LIBBPF_OPTS(bpf_iter_attach_opts, opts);
+       struct bpf_iter_test_kern5 *skel;
+       struct bpf_link *link;
+
+       skel = bpf_iter_test_kern5__open_and_load();
+       if (CHECK(!skel, "bpf_iter_test_kern5__open_and_load",
+                 "skeleton open_and_load failed\n"))
+               return;
+
+       opts.map_fd = bpf_map__fd(skel->maps.hashmap1);
+       link = bpf_program__attach_iter(skel->progs.dump_bpf_hash_map, &opts);
+       if (CHECK(!IS_ERR(link), "attach_iter", "unexpected success\n"))
+               bpf_link__destroy(link);
+
+       bpf_iter_test_kern5__destroy(skel);
+}
+
 void test_bpf_iter(void)
 {
        if (test__start_subtest("btf_id_or_null"))
@@ -911,4 +931,6 @@ void test_bpf_iter(void)
                test_bpf_percpu_array_map();
        if (test__start_subtest("bpf_sk_storage_map"))
                test_bpf_sk_storage_map();
+       if (test__start_subtest("rdonly-buf-out-of-bound"))
+               test_rdonly_buf_out_of_bound();
 }
diff --git a/tools/testing/selftests/bpf/progs/bpf_iter_test_kern5.c 
b/tools/testing/selftests/bpf/progs/bpf_iter_test_kern5.c
new file mode 100644
index 000000000000..e3a7575e81d2
--- /dev/null
+++ b/tools/testing/selftests/bpf/progs/bpf_iter_test_kern5.c
@@ -0,0 +1,35 @@
+// SPDX-License-Identifier: GPL-2.0
+/* Copyright (c) 2020 Facebook */
+#include "bpf_iter.h"
+#include <bpf/bpf_helpers.h>
+#include <bpf/bpf_tracing.h>
+
+char _license[] SEC("license") = "GPL";
+
+struct key_t {
+       int a;
+       int b;
+       int c;
+};
+
+struct {
+       __uint(type, BPF_MAP_TYPE_HASH);
+       __uint(max_entries, 3);
+       __type(key, struct key_t);
+       __type(value, __u64);
+} hashmap1 SEC(".maps");
+
+__u32 key_sum = 0;
+
+SEC("iter/bpf_map_elem")
+int dump_bpf_hash_map(struct bpf_iter__bpf_map_elem *ctx)
+{
+       void *key = ctx->key;
+
+       if (key == (void *)0)
+               return 0;
+
+       /* out of bound access w.r.t. hashmap1 */
+       key_sum += *(__u32 *)(key + sizeof(struct key_t));
+       return 0;
+}
-- 
2.24.1