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

["Emil Tsalapatis" <emil@etsalapatis.com>]

On Mon Jun 22, 2026 at 9:40 PM EDT, Sun Jian wrote:
> 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>

Reviewed-by: Emil Tsalapatis <emil@etsalapatis.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;
> +}