[PATCH bpf v2 2/2] selftests/bpf: add test for bpf_msg_pop_data() overflow

[Sechang Lim <rhkrqnwk98@gmail.com>]

Add a test in sockmap_basic.c that calls bpf_msg_pop_data() with a length
close to U32_MAX, which overflows the start + len bounds check. The sk_msg
program records the return value over a sendmsg and the test checks that
the call is rejected with -EINVAL.

Signed-off-by: Sechang Lim <rhkrqnwk98@gmail.com>
---
 .../selftests/bpf/prog_tests/sockmap_basic.c  | 48 +++++++++++++++++++
 .../bpf/progs/test_sockmap_msg_pop_data.c     | 27 +++++++++++
 2 files changed, 75 insertions(+)
 create mode 100644 tools/testing/selftests/bpf/progs/test_sockmap_msg_pop_data.c

diff --git a/tools/testing/selftests/bpf/prog_tests/sockmap_basic.c b/tools/testing/selftests/bpf/prog_tests/sockmap_basic.c
index d2846579285f..cb3229711f93 100644
--- a/tools/testing/selftests/bpf/prog_tests/sockmap_basic.c
+++ b/tools/testing/selftests/bpf/prog_tests/sockmap_basic.c
@@ -14,6 +14,7 @@
 #include "test_sockmap_pass_prog.skel.h"
 #include "test_sockmap_drop_prog.skel.h"
 #include "test_sockmap_change_tail.skel.h"
+#include "test_sockmap_msg_pop_data.skel.h"
 #include "bpf_iter_sockmap.skel.h"
 
 #include "sockmap_helpers.h"
@@ -666,6 +667,51 @@ static void test_sockmap_skb_verdict_change_tail(void)
 	test_sockmap_change_tail__destroy(skel);
 }
 
+static void test_sockmap_msg_verdict_pop_data(void)
+{
+	struct test_sockmap_msg_pop_data *skel;
+	int err, map, verdict;
+	int c1 = -1, p1 = -1, sent;
+	int zero = 0;
+	char *buf;
+	const size_t len = 32 * 1024;
+
+	skel = test_sockmap_msg_pop_data__open_and_load();
+	if (!ASSERT_OK_PTR(skel, "open_and_load"))
+		return;
+
+	verdict = bpf_program__fd(skel->progs.prog_msg_pop_data);
+	map = bpf_map__fd(skel->maps.sock_map);
+
+	err = bpf_prog_attach(verdict, map, BPF_SK_MSG_VERDICT, 0);
+	if (!ASSERT_OK(err, "bpf_prog_attach"))
+		goto out;
+
+	err = create_pair(AF_INET, SOCK_STREAM, &c1, &p1);
+	if (!ASSERT_OK(err, "create_pair"))
+		goto out;
+
+	err = bpf_map_update_elem(map, &zero, &c1, BPF_NOEXIST);
+	if (!ASSERT_OK(err, "bpf_map_update_elem"))
+		goto out_close;
+
+	buf = calloc(len, 1);
+	if (!ASSERT_OK_PTR(buf, "calloc"))
+		goto out_close;
+
+	sent = xsend(c1, buf, len, 0);
+	ASSERT_EQ(sent, (ssize_t)len, "xsend");
+	ASSERT_EQ(skel->data->pop_data_ret, -EINVAL, "pop_data_rejects overflow");
+
+	free(buf);
+
+out_close:
+	close(c1);
+	close(p1);
+out:
+	test_sockmap_msg_pop_data__destroy(skel);
+}
+
 static void test_sockmap_skb_verdict_peek_helper(int map)
 {
 	int err, c1, p1, zero = 0, sent, recvd, avail;
@@ -1373,6 +1419,8 @@ void test_sockmap_basic(void)
 		test_sockmap_skb_verdict_fionread(false);
 	if (test__start_subtest("sockmap skb_verdict change tail"))
 		test_sockmap_skb_verdict_change_tail();
+	if (test__start_subtest("sockmap msg_verdict pop_data overflow"))
+		test_sockmap_msg_verdict_pop_data();
 	if (test__start_subtest("sockmap skb_verdict msg_f_peek"))
 		test_sockmap_skb_verdict_peek();
 	if (test__start_subtest("sockmap skb_verdict msg_f_peek with link"))
diff --git a/tools/testing/selftests/bpf/progs/test_sockmap_msg_pop_data.c b/tools/testing/selftests/bpf/progs/test_sockmap_msg_pop_data.c
new file mode 100644
index 000000000000..301e65b95256
--- /dev/null
+++ b/tools/testing/selftests/bpf/progs/test_sockmap_msg_pop_data.c
@@ -0,0 +1,27 @@
+// SPDX-License-Identifier: GPL-2.0
+#include "vmlinux.h"
+#include <bpf/bpf_helpers.h>
+
+struct {
+	__uint(type, BPF_MAP_TYPE_SOCKMAP);
+	__uint(max_entries, 1);
+	__type(key, int);
+	__type(value, int);
+} sock_map SEC(".maps");
+
+#define POP_START 0x48a3
+#define POP_LEN   0xfffffffd
+
+long pop_data_ret = 1;
+
+SEC("sk_msg")
+int prog_msg_pop_data(struct sk_msg_md *msg)
+{
+	if (msg->size <= POP_START)
+		return SK_PASS;
+
+	pop_data_ret = bpf_msg_pop_data(msg, POP_START, POP_LEN, 0);
+	return SK_PASS;
+}
+
+char _license[] SEC("license") = "GPL";
-- 
2.43.0