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bpf/verifier: fix min/max handling in BPF_SUB 

We have to subtract the src max from the dst min, and vice-versa, since
 (e.g.) the smallest result comes from the largest subtrahend.

Fixes: 484611357c ("bpf: allow access into map value arrays")
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 14:37:34 +01:00 committed by David S. Miller
parent 545722cb0f
commit 9305706c2e
1 changed files with 15 additions and 6 deletions
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21
kernel/bpf/verifier.c
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@ -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: