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Merge branch 'bpf-fix-verifier-min-max-handling-in-BPF_SUB' 

Edward Cree says:

====================
bpf: fix verifier min/max handling in BPF_SUB

I managed to come up with a test for the swapped bounds in BPF_SUB, so here
 it is along with a patch that fixes it, separated out from my 'rewrite
 everything' series so it can go to -stable.
====================

Signed-off-by: David S. Miller <davem@davemloft.net>
This commit is contained in:
David S. Miller 2017-07-24 14:02:55 -07:00
parent 70dba204a3 9305706c2e
commit 1d9b86de37
2 changed files with 43 additions and 6 deletions
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21
kernel/bpf/verifier.c
View File

@ -1865,10 +1865,12 @@ static void adjust_reg_min_max_vals(struct bpf_verifier_env *env,
* do our normal operations to the register, we need to set the values
* to the min/max since they are undefined.
*/
if (min_val == BPF_REGISTER_MIN_RANGE)
dst_reg->min_value = BPF_REGISTER_MIN_RANGE;
if (max_val == BPF_REGISTER_MAX_RANGE)
dst_reg->max_value = BPF_REGISTER_MAX_RANGE;
if (opcode != BPF_SUB) {
if (min_val == BPF_REGISTER_MIN_RANGE)
dst_reg->min_value = BPF_REGISTER_MIN_RANGE;
if (max_val == BPF_REGISTER_MAX_RANGE)
dst_reg->max_value = BPF_REGISTER_MAX_RANGE;
}
switch (opcode) {
case BPF_ADD:
@ -1879,10 +1881,17 @@ static void adjust_reg_min_max_vals(struct bpf_verifier_env *env,
dst_reg->min_align = min(src_align, dst_align);
break;
case BPF_SUB:
/* If one of our values was at the end of our ranges, then the
* _opposite_ value in the dst_reg goes to the end of our range.
*/
if (min_val == BPF_REGISTER_MIN_RANGE)
dst_reg->max_value = BPF_REGISTER_MAX_RANGE;
if (max_val == BPF_REGISTER_MAX_RANGE)
dst_reg->min_value = BPF_REGISTER_MIN_RANGE;
if (dst_reg->min_value != BPF_REGISTER_MIN_RANGE)
dst_reg->min_value -= min_val;
dst_reg->min_value -= max_val;
if (dst_reg->max_value != BPF_REGISTER_MAX_RANGE)
dst_reg->max_value -= max_val;
dst_reg->max_value -= min_val;
dst_reg->min_align = min(src_align, dst_align);
break;
case BPF_MUL:

28
tools/testing/selftests/bpf/test_verifier.c
View File

@ -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)