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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: Stanislav Fomichev <sdf@google.com>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
This commit is contained in:
Stanislav Fomichev 2019-04-22 08:55:49 -07:00 committed by Daniel Borkmann
parent c43f1255b8
commit c9cb2c1e11
1 changed files with 48 additions and 0 deletions
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48
tools/testing/selftests/bpf/prog_tests/flow_dissector_load_bytes.c Normal file
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// 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);
}