bpf: Rework ptr_limit into alu_limit and add common error path

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>

diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
index a21d7f1..b8e0171 100644 (file)
--- a/kernel/bpf/verifier.c
+++ b/kernel/bpf/verifier.c
@@ -5858,12 +5858,12 @@ static struct bpf_insn_aux_data *cur_aux(struct bpf_verifier_env *env)
 
 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))
@@ -5880,22 +5880,27 @@ static int retrieve_ptr_limit(const struct bpf_reg_state *ptr_reg,
                 */
                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,