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py: Add MICROPY_PY_STRUCT_UNSAFE_TYPECODES.

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This is useful to turn off when fuzzing, as improper use of these
typecodes can crash MicroPython.

Signed-off-by: Jeff Epler <jepler@gmail.com>
This commit is contained in:
Jeff Epler 2025-07-21 13:31:59 -05:00
parent 658a2e3dbd
commit 05f3f8d66e
2 changed files with 23 additions and 4 deletions
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16
py/binary.c
View file

@ -69,11 +69,13 @@ size_t mp_binary_get_size(char struct_type, char val_type, size_t *palign) {
case 'Q':
size = 8;
break;
#if MICROPY_PY_STRUCT_UNSAFE_TYPECODES
case 'P':
case 'O':
case 'S':
size = sizeof(void *);
break;
#endif
case 'e':
size = 2;
break;
@ -119,12 +121,14 @@ size_t mp_binary_get_size(char struct_type, char val_type, size_t *palign) {
align = alignof(long long);
size = sizeof(long long);
break;
#if MICROPY_PY_STRUCT_UNSAFE_TYPECODES
case 'P':
case 'O':
case 'S':
align = alignof(void *);
size = sizeof(void *);
break;
#endif
case 'e':
align = 2;
size = 2;
@ -281,11 +285,13 @@ mp_obj_t mp_binary_get_val_array(char typecode, void *p, size_t index) {
return mp_obj_new_float_from_d(((double *)p)[index]);
#endif
// Extension to CPython: array of objects
#if MICROPY_PY_STRUCT_UNSAFE_TYPECODES
case 'O':
return ((mp_obj_t *)p)[index];
// Extension to CPython: array of pointers
case 'P':
return mp_obj_new_int((mp_int_t)(uintptr_t)((void **)p)[index]);
#endif
}
return MP_OBJ_NEW_SMALL_INT(val);
}
@ -334,9 +340,9 @@ mp_obj_t mp_binary_get_val(char struct_type, char val_type, byte *p_base, byte *
long long val = mp_binary_get_int(size, is_signed(val_type), (struct_type == '>'), p);
if (val_type == 'O') {
if (MICROPY_PY_STRUCT_UNSAFE_TYPECODES && val_type == 'O') {
return (mp_obj_t)(mp_uint_t)val;
} else if (val_type == 'S') {
} else if (MICROPY_PY_STRUCT_UNSAFE_TYPECODES && val_type == 'S') {
const char *s_val = (const char *)(uintptr_t)(mp_uint_t)val;
return mp_obj_new_str_from_cstr(s_val);
#if MICROPY_PY_BUILTINS_FLOAT
@ -407,9 +413,11 @@ void mp_binary_set_val(char struct_type, char val_type, mp_obj_t val_in, byte *p
mp_uint_t val;
switch (val_type) {
#if MICROPY_PY_STRUCT_UNSAFE_TYPECODES
case 'O':
val = (mp_uint_t)val_in;
break;
#endif
#if MICROPY_PY_BUILTINS_FLOAT
case 'e':
val = mp_encode_half_float(mp_obj_get_float_to_f(val_in));
@ -474,10 +482,12 @@ void mp_binary_set_val_array(char typecode, void *p, size_t index, mp_obj_t val_
((double *)p)[index] = mp_obj_get_float_to_d(val_in);
break;
#endif
#if MICROPY_PY_STRUCT_UNSAFE_TYPECODES
// Extension to CPython: array of objects
case 'O':
((mp_obj_t *)p)[index] = val_in;
break;
#endif
default:
#if MICROPY_LONGINT_IMPL != MICROPY_LONGINT_IMPL_NONE
if (mp_obj_is_exact_type(val_in, &mp_type_int)) {
@ -535,8 +545,10 @@ void mp_binary_set_val_array_from_int(char typecode, void *p, size_t index, mp_i
break;
#endif
// Extension to CPython: array of pointers
#if MICROPY_PY_STRUCT_UNSAFE_TYPECODES
case 'P':
((void **)p)[index] = (void *)(uintptr_t)val;
break;
#endif
}
}

7
py/mpconfig.h
View file

@ -1601,6 +1601,13 @@ typedef time_t mp_timestamp_t;
#define MICROPY_PY_STRUCT (MICROPY_CONFIG_ROM_LEVEL_AT_LEAST_CORE_FEATURES)
#endif
// Whether struct module provides unsafe and non-standard typecodes O, P, S.
// These typecodes are not in CPython and can cause crashes by accessing arbitrary
// memory.
#ifndef MICROPY_PY_STRUCT_UNSAFE_TYPECODES
#define MICROPY_PY_STRUCT_UNSAFE_TYPECODES (1)
#endif
// Whether to provide "sys" module
#ifndef MICROPY_PY_SYS
#define MICROPY_PY_SYS (MICROPY_CONFIG_ROM_LEVEL_AT_LEAST_CORE_FEATURES)