[PATCH 5.11 120/122] bpf: Rework ptr_limit into alu_limit and add common error path

Greg Kroah-Hartman
2021-04-19T13:17:15Z

From: Daniel Borkmann <daniel@iogearbox.net>

commit b658bbb844e28f1862867f37e8ca11a8e2aa94a3 upstream.

Small refactor with no semantic changes in order to consolidate the max
ptr_limit boundary check.

Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Reviewed-by: John Fastabend <john.fastabend@gmail.com>
Acked-by: Alexei Starovoitov <ast@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
kernel/bpf/verifier.c | 21 +++++++++++++--------
1 file changed, 13 insertions(+), 8 deletions(-)

--- a/kernel/bpf/verifier.c
+++ b/kernel/bpf/verifier.c
@@ -5386,12 +5386,12 @@ static struct bpf_insn_aux_data *cur_aux

static int retrieve_ptr_limit(const struct bpf_reg_state *ptr_reg,
const struct bpf_reg_state *off_reg,
- u32 *ptr_limit, u8 opcode)
+ u32 *alu_limit, u8 opcode)
{
bool off_is_neg = off_reg->smin_value < 0;
bool mask_to_left = (opcode == BPF_ADD && off_is_neg) ||
(opcode == BPF_SUB && !off_is_neg);
- u32 off, max;
+ u32 off, max = 0, ptr_limit = 0;

if (!tnum_is_const(off_reg->var_off) &&
(off_reg->smin_value < 0) != (off_reg->smax_value < 0))
@@ -5408,22 +5408,27 @@ static int retrieve_ptr_limit(const stru
*/
off = ptr_reg->off + ptr_reg->var_off.value;
if (mask_to_left)
- *ptr_limit = MAX_BPF_STACK + off;
+ ptr_limit = MAX_BPF_STACK + off;
else
- *ptr_limit = -off - 1;
- return *ptr_limit >= max ? -ERANGE : 0;
+ ptr_limit = -off - 1;
+ break;
case PTR_TO_MAP_VALUE:
max = ptr_reg->map_ptr->value_size;
if (mask_to_left) {
- *ptr_limit = ptr_reg->umax_value + ptr_reg->off;
+ ptr_limit = ptr_reg->umax_value + ptr_reg->off;
} else {
off = ptr_reg->smin_value + ptr_reg->off;
- *ptr_limit = ptr_reg->map_ptr->value_size - off - 1;
+ ptr_limit = ptr_reg->map_ptr->value_size - off - 1;
}
- return *ptr_limit >= max ? -ERANGE : 0;
+ break;
default:
return -EINVAL;
}
+
+ if (ptr_limit >= max)
+ return -ERANGE;
+ *alu_limit = ptr_limit;
+ return 0;
}

static bool can_skip_alu_sanitation(const struct bpf_verifier_env *env,