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Groups > linux.kernel > #1693747
| From | Daniel Borkmann <daniel@iogearbox.net> |
|---|---|
| Newsgroups | linux.kernel |
| Subject | Re: [PATCH net 1/2] selftests/bpf: subtraction bounds test |
| Date | 2017-07-21 16:30 +0200 |
| Message-ID | <u5H6h-5Wt-1@gated-at.bofh.it> (permalink) |
| References | <u5GjT-5qP-9@gated-at.bofh.it> <u5GjT-5qP-7@gated-at.bofh.it> |
| Organization | linux.* mail to news gateway |
On 07/21/2017 03:36 PM, Edward Cree wrote:
> There is a bug in the verifier's handling of BPF_SUB: [a,b] - [c,d] yields
> was [a-c, b-d] rather than the correct [a-d, b-c]. So here is a test
> which, with the bogus handling, will produce ranges of [0,0] and thus
> allowed accesses; whereas the correct handling will give a range of
> [-255, 255] (and hence the right-shift will give a range of [0, 255]) and
> the accesses will be rejected.
>
> Signed-off-by: Edward Cree <ecree@solarflare.com>
Acked-by: Daniel Borkmann <daniel@iogearbox.net>
> tools/testing/selftests/bpf/test_verifier.c | 28 ++++++++++++++++++++++++++++
> 1 file changed, 28 insertions(+)
>
> diff --git a/tools/testing/selftests/bpf/test_verifier.c b/tools/testing/selftests/bpf/test_verifier.c
> index af7d173..addea82 100644
> --- a/tools/testing/selftests/bpf/test_verifier.c
> +++ b/tools/testing/selftests/bpf/test_verifier.c
> @@ -5980,6 +5980,34 @@ static struct bpf_test tests[] = {
> .result = REJECT,
> .result_unpriv = REJECT,
> },
> + {
> + "subtraction bounds (map value)",
> + .insns = {
> + BPF_ST_MEM(BPF_DW, BPF_REG_10, -8, 0),
> + BPF_MOV64_REG(BPF_REG_2, BPF_REG_10),
> + BPF_ALU64_IMM(BPF_ADD, BPF_REG_2, -8),
> + BPF_LD_MAP_FD(BPF_REG_1, 0),
> + BPF_RAW_INSN(BPF_JMP | BPF_CALL, 0, 0, 0,
> + BPF_FUNC_map_lookup_elem),
> + BPF_JMP_IMM(BPF_JEQ, BPF_REG_0, 0, 9),
> + BPF_LDX_MEM(BPF_B, BPF_REG_1, BPF_REG_0, 0),
> + BPF_JMP_IMM(BPF_JGT, BPF_REG_1, 0xff, 7),
> + BPF_LDX_MEM(BPF_B, BPF_REG_3, BPF_REG_0, 1),
> + BPF_JMP_IMM(BPF_JGT, BPF_REG_3, 0xff, 5),
> + BPF_ALU64_REG(BPF_SUB, BPF_REG_1, BPF_REG_3),
> + BPF_ALU64_IMM(BPF_RSH, BPF_REG_1, 56),
> + BPF_ALU64_REG(BPF_ADD, BPF_REG_0, BPF_REG_1),
> + BPF_LDX_MEM(BPF_B, BPF_REG_0, BPF_REG_0, 0),
> + BPF_EXIT_INSN(),
> + BPF_MOV64_IMM(BPF_REG_0, 0),
> + BPF_EXIT_INSN(),
> + },
> + .fixup_map1 = { 3 },
> + .errstr_unpriv = "R0 pointer arithmetic prohibited",
> + .errstr = "R0 min value is negative, either use unsigned index or do a if (index >=0) check.",
> + .result = REJECT,
> + .result_unpriv = REJECT,
> + },
> };
>
> static int probe_filter_length(const struct bpf_insn *fp)
>
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[PATCH net 1/2] selftests/bpf: subtraction bounds test Edward Cree <ecree@solarflare.com> - 2017-07-21 15:40 +0200 Re: [PATCH net 1/2] selftests/bpf: subtraction bounds test Daniel Borkmann <daniel@iogearbox.net> - 2017-07-21 16:30 +0200
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