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 <ec...@solarflare.com>
Acked-by: Daniel Borkmann <dan...@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)
