[PATCH bpf v4] selftests/bpf: Cover partial copy of non-linear test_run output

[Sun Jian <sun.jian.kdev@gmail.com>]

prog_run_opts already verifies that BPF_PROG_TEST_RUN returns -ENOSPC
for a short data_out buffer while still reporting the full output size
through data_size_out.

Add the same coverage for non-linear test_run output. Use pass-through
TC and XDP programs with a 9000-byte packet, a 64-byte linear data area,
and a 100-byte data_out buffer. The expected output spans both the linear
data and the first fragment.

Verify that test_run returns -ENOSPC, reports the full packet length
through data_size_out, and copies the packet prefix into data_out for
both non-linear skb and XDP frags paths.

Signed-off-by: Sun Jian <sun.jian.kdev@gmail.com>
---

v4:
- Send only the selftest patch; the fix patch has been applied to bpf/master.
- Initialize data_out buffers to avoid reading uninitialized stack memory if
  bpf_prog_test_run_opts() fails unexpectedly.

 .../selftests/bpf/prog_tests/prog_run_opts.c  | 70 +++++++++++++++++++
 .../selftests/bpf/progs/test_pkt_access.c     | 12 ++++
 2 files changed, 82 insertions(+)

diff --git a/tools/testing/selftests/bpf/prog_tests/prog_run_opts.c b/tools/testing/selftests/bpf/prog_tests/prog_run_opts.c
index 01f1d1b6715a..beb6fa78fd94 100644
--- a/tools/testing/selftests/bpf/prog_tests/prog_run_opts.c
+++ b/tools/testing/selftests/bpf/prog_tests/prog_run_opts.c
@@ -4,6 +4,10 @@
 
 #include "test_pkt_access.skel.h"
 
+#define NONLINEAR_PKT_LEN 9000
+#define NONLINEAR_LINEAR_DATA_LEN 64
+#define SHORT_OUT_LEN 100
+
 static const __u32 duration;
 
 static void check_run_cnt(int prog_fd, __u64 run_cnt)
@@ -20,6 +24,69 @@ static void check_run_cnt(int prog_fd, __u64 run_cnt)
 	      "incorrect number of repetitions, want %llu have %llu\n", run_cnt, info.run_cnt);
 }
 
+static void init_pkt(__u8 *pkt, size_t len)
+{
+	size_t i;
+
+	for (i = 0; i < len; i++)
+		pkt[i] = i & 0xff;
+}
+
+static void test_skb_nonlinear_data_out_partial(struct test_pkt_access *skel)
+{
+	LIBBPF_OPTS(bpf_test_run_opts, topts);
+	__u8 pkt[NONLINEAR_PKT_LEN];
+	__u8 out[SHORT_OUT_LEN] = {};
+	struct __sk_buff skb = {};
+	int prog_fd, err;
+
+	init_pkt(pkt, sizeof(pkt));
+
+	skb.data_end = NONLINEAR_LINEAR_DATA_LEN;
+
+	topts.data_in = pkt;
+	topts.data_size_in = sizeof(pkt);
+	topts.data_out = out;
+	topts.data_size_out = sizeof(out);
+	topts.ctx_in = &skb;
+	topts.ctx_size_in = sizeof(skb);
+
+	prog_fd = bpf_program__fd(skel->progs.tc_pass_prog);
+	err = bpf_prog_test_run_opts(prog_fd, &topts);
+
+	ASSERT_EQ(err, -ENOSPC, "skb_partial_err");
+	ASSERT_EQ(topts.data_size_out, sizeof(pkt), "skb_partial_size");
+	ASSERT_OK(memcmp(out, pkt, sizeof(out)), "skb_partial_data");
+}
+
+static void test_xdp_nonlinear_data_out_partial(struct test_pkt_access *skel)
+{
+	LIBBPF_OPTS(bpf_test_run_opts, topts);
+	__u8 pkt[NONLINEAR_PKT_LEN];
+	__u8 out[SHORT_OUT_LEN] = {};
+	struct xdp_md ctx = {};
+	int prog_fd, err;
+
+	init_pkt(pkt, sizeof(pkt));
+
+	ctx.data = 0;
+	ctx.data_end = NONLINEAR_LINEAR_DATA_LEN;
+
+	topts.data_in = pkt;
+	topts.data_size_in = sizeof(pkt);
+	topts.data_out = out;
+	topts.data_size_out = sizeof(out);
+	topts.ctx_in = &ctx;
+	topts.ctx_size_in = sizeof(ctx);
+
+	prog_fd = bpf_program__fd(skel->progs.xdp_frags_pass_prog);
+	err = bpf_prog_test_run_opts(prog_fd, &topts);
+
+	ASSERT_EQ(err, -ENOSPC, "xdp_partial_err");
+	ASSERT_EQ(topts.data_size_out, sizeof(pkt), "xdp_partial_size");
+	ASSERT_OK(memcmp(out, pkt, sizeof(out)), "xdp_partial_data");
+}
+
 void test_prog_run_opts(void)
 {
 	struct test_pkt_access *skel;
@@ -69,6 +136,9 @@ void test_prog_run_opts(void)
 	run_cnt += topts.repeat;
 	check_run_cnt(prog_fd, run_cnt);
 
+	test_skb_nonlinear_data_out_partial(skel);
+	test_xdp_nonlinear_data_out_partial(skel);
+
 cleanup:
 	if (skel)
 		test_pkt_access__destroy(skel);
diff --git a/tools/testing/selftests/bpf/progs/test_pkt_access.c b/tools/testing/selftests/bpf/progs/test_pkt_access.c
index bce7173152c6..cd284401eebd 100644
--- a/tools/testing/selftests/bpf/progs/test_pkt_access.c
+++ b/tools/testing/selftests/bpf/progs/test_pkt_access.c
@@ -150,3 +150,15 @@ int test_pkt_access(struct __sk_buff *skb)
 
 	return TC_ACT_UNSPEC;
 }
+
+SEC("tc")
+int tc_pass_prog(struct __sk_buff *skb)
+{
+	return TC_ACT_OK;
+}
+
+SEC("xdp.frags")
+int xdp_frags_pass_prog(struct xdp_md *ctx)
+{
+	return XDP_PASS;
+}
-- 
2.43.0