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selftests/bpf: subtraction bounds test

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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>
Signed-off-by: David S. Miller <davem@davemloft.net>
This commit is contained in:
Edward Cree 2017-07-21 14:36:57 +01:00 committed by David S. Miller
parent 70dba204a3
commit 545722cb0f
1 changed files with 28 additions and 0 deletions
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28
tools/testing/selftests/bpf/test_verifier.c
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@ -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)