[PATCH bpf-next v4 02/11] bpf: check scalar or invalid register in check_helper_mem_access

[Lorenz Bauer]

Move the check for a NULL or zero register to check_helper_mem_access. This
makes check_stack_boundary easier to understand.

Signed-off-by: Lorenz Bauer <l...@cloudflare.com>
Acked-by: Andrii Nakryiko <andr...@fb.com>
---
 kernel/bpf/verifier.c | 24 +++++++++++-------------
 1 file changed, 11 insertions(+), 13 deletions(-)

diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
index 814bc6c1ad16..c997f81c500b 100644
--- a/kernel/bpf/verifier.c
+++ b/kernel/bpf/verifier.c
@@ -3594,18 +3594,6 @@ static int check_stack_boundary(struct bpf_verifier_env 
*env, int regno,
        struct bpf_func_state *state = func(env, reg);
        int err, min_off, max_off, i, j, slot, spi;
 
-       if (reg->type != PTR_TO_STACK) {
-               /* Allow zero-byte read from NULL, regardless of pointer type */
-               if (zero_size_allowed && access_size == 0 &&
-                   register_is_null(reg))
-                       return 0;
-
-               verbose(env, "R%d type=%s expected=%s\n", regno,
-                       reg_type_str[reg->type],
-                       reg_type_str[PTR_TO_STACK]);
-               return -EACCES;
-       }
-
        if (tnum_is_const(reg->var_off)) {
                min_off = max_off = reg->var_off.value + reg->off;
                err = __check_stack_boundary(env, regno, min_off, access_size,
@@ -3750,9 +3738,19 @@ static int check_helper_mem_access(struct 
bpf_verifier_env *env, int regno,
                                           access_size, zero_size_allowed,
                                           "rdwr",
                                           &env->prog->aux->max_rdwr_access);
-       default: /* scalar_value|ptr_to_stack or invalid ptr */
+       case PTR_TO_STACK:
                return check_stack_boundary(env, regno, access_size,
                                            zero_size_allowed, meta);
+       default: /* scalar_value or invalid ptr */
+               /* Allow zero-byte read from NULL, regardless of pointer type */
+               if (zero_size_allowed && access_size == 0 &&
+                   register_is_null(reg))
+                       return 0;
+
+               verbose(env, "R%d type=%s expected=%s\n", regno,
+                       reg_type_str[reg->type],
+                       reg_type_str[PTR_TO_STACK]);
+               return -EACCES;
        }
 }
 
-- 
2.25.1