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extmod/vfs_posix: Add MICROPY_VFS_POSIX_WRITABLE option.

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When this configuration flag is set, VfsPosix instances can be written.
Otherwise, they will always be created "read only".

This flag is useful when fuzzing micropython: Without VfsPosix, the fuzzing
input script cannot be read; but with writable VfsPosix, fuzzing scripts
can potentially perform undesired operations on the host filesystem.

Signed-off-by: Jeff Epler <jepler@gmail.com>
This commit is contained in:
Jeff Epler
2025-07-19 06:38:18 -05:00
committed by Damien George
parent 3c603f7baf
commit 59ee59901b
2 changed files with 7 additions and 2 deletions
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4
extmod/vfs_posix.c
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@@ -137,7 +137,7 @@ static mp_obj_t vfs_posix_make_new(const mp_obj_type_t *type, size_t n_args, siz
vstr_add_char(&vfs->root, '/'); vstr_add_char(&vfs->root, '/');
} }
vfs->root_len = vfs->root.len; vfs->root_len = vfs->root.len;
vfs->readonly = false; vfs->readonly = !MICROPY_VFS_POSIX_WRITABLE;
return MP_OBJ_FROM_PTR(vfs); return MP_OBJ_FROM_PTR(vfs);
} }
@@ -161,7 +161,7 @@ static mp_obj_t vfs_posix_umount(mp_obj_t self_in) {
static MP_DEFINE_CONST_FUN_OBJ_1(vfs_posix_umount_obj, vfs_posix_umount); static MP_DEFINE_CONST_FUN_OBJ_1(vfs_posix_umount_obj, vfs_posix_umount);
static inline bool vfs_posix_is_readonly(mp_obj_vfs_posix_t *self) { static inline bool vfs_posix_is_readonly(mp_obj_vfs_posix_t *self) {
return self->readonly; return !MICROPY_VFS_POSIX_WRITABLE || self->readonly;
} }
static void vfs_posix_require_writable(mp_obj_t self_in) { static void vfs_posix_require_writable(mp_obj_t self_in) {

5
py/mpconfig.h
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@@ -1084,6 +1084,11 @@ typedef time_t mp_timestamp_t;
#define MICROPY_VFS_POSIX (0) #define MICROPY_VFS_POSIX (0)
#endif #endif
// Whether to include support for writable POSIX filesystems.
#ifndef MICROPY_VFS_POSIX_WRITABLE
#define MICROPY_VFS_POSIX_WRITABLE (1)
#endif
// Support for VFS FAT component, to mount a FAT filesystem within VFS // Support for VFS FAT component, to mount a FAT filesystem within VFS
#ifndef MICROPY_VFS_FAT #ifndef MICROPY_VFS_FAT
#define MICROPY_VFS_FAT (0) #define MICROPY_VFS_FAT (0)