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MicroPython type confusion in star imports causes interpreter crash #19621
Description
Activity
Thanks for the report.
To fix it, either check the object stored to
__dict__is a dict (like CPython does), or disallow storing to__dict__altogether (because probably MicroPython doesn't have the right semantics if you do store to dict).(It's not really a security vulnerability, because if you can run arbitrary Python code, there are many ways to crash the interpreter.)
Reacted by Vectrain51Thanks for the clarification. I agree with your assessment that this is better treated as a robustness bug rather than a security vulnerability, given that arbitrary Python execution already allows the interpreter to be terminated in other ways.
Thanks as well for looking into the fix options. :)
I'll send a PR for this: check that
__dict__is a dict (or OrderedDict) inmp_import_allbefore callingmp_obj_dict_get_map.There is a separate
mp_import_allcrash after the__dict__type check discussed here: module__getattr__can clear the__all__list while the importer retains its old items pointer.Revalidated on current
master(a129b2fba1a3348088c94d0462eef16d20874dea); every case reproduced in 3/3 runs.Build:
VARIANT=coveragewith the repository's official ASan flags:-fsanitize=address --param asan-use-after-return=0 -DMP_ASAN=1.Additional reproductions
Module
__getattr__clears__all__during star importimport sys sys.path.insert(0, "/tmp") open("/tmp/reentrant_clear.py", "w").write( "__all__=['a','b','c','d']\n" "def __getattr__(name):\n" " __all__.clear()\n" " return 123\n" ) from reentrant_clear import * print(a)
Observed:
SUMMARY: AddressSanitizer: SEGV ../../py/objstr.c:2534 in mp_obj_str_get_qstrComplete ASan output
AddressSanitizer:DEADLYSIGNAL ================================================================= ==82==ERROR: AddressSanitizer: SEGV on unknown address 0x000000000000 (pc 0xaaaad5749a88 bp 0xffffdbdee630 sp 0xffffdbdee630 T0) ==82==The signal is caused by a READ memory access. ==82==Hint: address points to the zero page. #0 0xaaaad5749a88 in mp_obj_str_get_qstr ../../py/objstr.c:2534 #1 0xaaaad571012c in mp_import_all ../../py/runtime.c:1613 #2 0xaaaad5776708 in mp_execute_bytecode ../../py/vm.c:1277 #3 0xaaaad5730c64 in fun_bc_call ../../py/objfun.c:294 #4 0xaaaad5710618 in mp_call_function_n_kw ../../py/runtime.c:719 #5 0xaaaad5714720 in mp_call_function_0 ../../py/runtime.c:693 #6 0xaaaad589a60c in parse_compile_execute ../../shared/runtime/pyexec.c:137 #7 0xaaaad589b774 in pyexec_file ../../shared/runtime/pyexec.c:739 #8 0xaaaad58903f0 in do_file /src/ports/unix/main.c:269 #9 0xaaaad5891a18 in main_ /src/ports/unix/main.c:692 #10 0xaaaad5892000 in main /src/ports/unix/main.c:452 #11 0xffff83862258 (/lib/aarch64-linux-gnu/libc.so.6+0x22258) (BuildId: 4c1eca4527d1163b2dde55860b69f270158febb4) #12 0xffff83862338 in __libc_start_main (/lib/aarch64-linux-gnu/libc.so.6+0x22338) (BuildId: 4c1eca4527d1163b2dde55860b69f270158febb4) #13 0xaaaad56cccac in _start (/workspace/work/micropython-current/ports/unix/build-asan-linux-official/micropython+0x19ccac) (BuildId: d745232daadafece431463287d3aa5e506209b85) AddressSanitizer can not provide additional info. SUMMARY: AddressSanitizer: SEGV ../../py/objstr.c:2534 in mp_obj_str_get_qstr ==82==ABORTINGWould you prefer a separate issue for any of these paths?
Tracking references: MicroPython-26.
Port, board and/or hardware
No response
MicroPython version
No response
Issue Report
Summary
MicroPython
v1.29.0-previewcan be crashed by a Python script that places a non-dictionary value in an object's__dict__attribute and then executesfrom module import *. The import path passes the value tomp_obj_dict_get_map()without validating its type.Affected version tested:
Details
Relevant source:
py/runtime.c,mp_import_all().The public interpreter flow is:
An instance member named
__dict__can contain a non-dictionary value, which the import code treats as a native dictionary.PoC
Build the Unix port from the tested tag:
git clone https://github.com/micropython/micropython.git cd micropython git checkout v1.29.0-preview make -C ports/unixRun the script through the built interpreter:
Observed:
Impact
An attacker able to supply Python code to a MicroPython runtime can terminate the interpreter through the public
from ... import *language feature. Remote exploitation depends on an application that executes attacker-controlled MicroPython code.Code of Conduct
Yes, I agree