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Commit c9cb2c1e authored by Stanislav Fomichev's avatar Stanislav Fomichev Committed by Daniel Borkmann
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selftests/bpf: add flow dissector bpf_skb_load_bytes helper test 



When flow dissector is called without skb, we want to make sure
bpf_skb_load_bytes invocations return error. Add small test which tries
to read single byte from a packet.

bpf_skb_load_bytes should always fail under BPF_PROG_TEST_RUN because
it was converted to the skb-less mode.

Signed-off-by: default avatarStanislav Fomichev <sdf@google.com>
Signed-off-by: default avatarDaniel Borkmann <daniel@iogearbox.net>
parent c43f1255

tools/testing/selftests/bpf/prog_tests/flow_dissector_load_bytes.c

0 → 100644
+48 −0
Original line number Diff line number Diff line 
// SPDX-License-Identifier: GPL-2.0

#include <test_progs.h>



void test_flow_dissector_load_bytes(void)

{

	struct bpf_flow_keys flow_keys;

	__u32 duration = 0, retval, size;

	struct bpf_insn prog[] = {

		// BPF_REG_1 - 1st argument: context

		// BPF_REG_2 - 2nd argument: offset, start at first byte

		BPF_MOV64_IMM(BPF_REG_2, 0),

		// BPF_REG_3 - 3rd argument: destination, reserve byte on stack

		BPF_ALU64_REG(BPF_MOV, BPF_REG_3, BPF_REG_10),

		BPF_ALU64_IMM(BPF_ADD, BPF_REG_3, -1),

		// BPF_REG_4 - 4th argument: copy one byte

		BPF_MOV64_IMM(BPF_REG_4, 1),

		// bpf_skb_load_bytes(ctx, sizeof(pkt_v4), ptr, 1)

		BPF_RAW_INSN(BPF_JMP | BPF_CALL, 0, 0, 0,

			     BPF_FUNC_skb_load_bytes),

		BPF_JMP_IMM(BPF_JNE, BPF_REG_0, 0, 2),

		// if (ret == 0) return BPF_DROP (2)

		BPF_MOV64_IMM(BPF_REG_0, BPF_DROP),

		BPF_EXIT_INSN(),

		// if (ret != 0) return BPF_OK (0)

		BPF_MOV64_IMM(BPF_REG_0, BPF_OK),

		BPF_EXIT_INSN(),

	};

	int fd, err;



	/* make sure bpf_skb_load_bytes is not allowed from skb-less context

	 */

	fd = bpf_load_program(BPF_PROG_TYPE_FLOW_DISSECTOR, prog,

			      ARRAY_SIZE(prog), "GPL", 0, NULL, 0);

	CHECK(fd < 0,

	      "flow_dissector-bpf_skb_load_bytes-load",

	      "fd %d errno %d\n",

	      fd, errno);



	err = bpf_prog_test_run(fd, 1, &pkt_v4, sizeof(pkt_v4),

				&flow_keys, &size, &retval, &duration);

	CHECK(size != sizeof(flow_keys) || err || retval != 1,

	      "flow_dissector-bpf_skb_load_bytes",

	      "err %d errno %d retval %d duration %d size %u/%zu\n",

	      err, errno, retval, duration, size, sizeof(flow_keys));



	if (fd >= -1)

		close(fd);

}