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C library hygiene: Avoid enums in public interfaces for FFI compatibility #3

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amboar opened this issue Nov 3, 2022 · 0 comments
Open

C library hygiene: Avoid enums in public interfaces for FFI compatibility #3

amboar opened this issue Nov 3, 2022 · 0 comments

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@amboar
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amboar commented Nov 3, 2022

WG14/N1256 (C99 draft standard) 6.7.2.2 paragraph 4 states:

Each enumerated type shall be compatible with char, a signed integer type, or an unsigned integer type. The choice of type is implementation-defined,110) but shall be capable of representing the values of all the members of the enumeration. The enumerated type is incomplete until after the } that terminates the list of enumerator declarations.

with the footnote:

  1. An implementation may delay the choice of which integer type until all enumeration constants have been seen.

Thus it's not possible to infer without further platform ABI, C compiler and library version information how the enum type will be represented in terms of storage. Further, given the footnote, the size of the underlying storage for the enum may change over time if additional members are added to the enum. These facts in turn makes it hard to e,g, create reliable FFI bindings for the library. IMO use of enums in public APIs should be avoided, and use of explicitly sized types and macros for named constants should be preferred.
bradbishop pushed a commit that referenced this issue Apr 19, 2023
@amboar
tests: platform: Fix TEST(GetStateSensorReadings, testBadDecodeResponse)
6ad4dc0 
Fix up an off-by-one error in the test suite. I modified the test to
instead report more sensors than were present in the message buffer and
received the following from ASAN:

```
=================================================================
==297936==ERROR: AddressSanitizer: stack-buffer-overflow on address 0xffffc18300b9 at pc 0xffffa04cae2c bp 0xffffc182fe40 sp 0xffffc182fe58
READ of size 1 at 0xffffc18300b9 thread T0
    #0 0xffffa04cae28 in pldm_msgbuf_extract_uint8 ../src/msgbuf/../msgbuf.h:129
    #1 0xffffa04cae28 in decode_get_state_sensor_readings_resp ../src/platform.c:804
    #2 0x2c0278 in GetStateSensorReadings_testBadDecodeResponse_Test::TestBody() ../tests/libpldm_platform_test.cpp:843
    #3 0xffffa03ba0f8 in void testing::internal::HandleExceptionsInMethodIfSupported<testing::Test, void>(testing::Test*, void (testing::Test::*)(), char const*) (/lib64/libgtest.so.1.12.1+0x4a0f8)
    #4 0xffffa03a6680 in testing::Test::Run() (/lib64/libgtest.so.1.12.1+0x36680)
    #5 0xffffa03a688c in testing::TestInfo::Run() (/lib64/libgtest.so.1.12.1+0x3688c)
    #6 0xffffa03a6c30 in testing::TestSuite::Run() (/lib64/libgtest.so.1.12.1+0x36c30)
    #7 0xffffa03b2dd0 in testing::internal::UnitTestImpl::RunAllTests() (/lib64/libgtest.so.1.12.1+0x42dd0)
    #8 0xffffa03b1998 in testing::UnitTest::Run() (/lib64/libgtest.so.1.12.1+0x41998)
    #9 0xffffa0400940 in main (/lib64/libgtest_main.so.1.12.1+0x940)
    #10 0xffff9f80b584 in __libc_start_call_main (/lib64/libc.so.6+0x2b584)
    #11 0xffff9f80b65c in __libc_start_main@@GLIBC_2.34 (/lib64/libc.so.6+0x2b65c)
    #12 0x2b2a6c in _start (/mnt/host/andrew/src/openbmc/libpldm/build/tests/libpldm_platform_test+0x2b2a6c)

Address 0xffffc18300b9 is located in stack of thread T0 at offset 297 in frame
    #0 0x2bfe90 in GetStateSensorReadings_testBadDecodeResponse_Test::TestBody() ../tests/libpldm_platform_test.cpp:811

  This frame has 14 object(s):
    [48, 49) 'retcompletion_code' (line 831)
    [64, 65) 'retcomp_sensorCnt' (line 832)
    [80, 84) 'rc' (line 819)
    [96, 100) '<unknown>'
    [112, 116) 'stateField' (line 827)
    [128, 132) 'retstateField' (line 833)
    [144, 148) '<unknown>'
    [160, 168) '<unknown>'
    [192, 200) '<unknown>'
    [224, 232) '<unknown>'
    [256, 264) '<unknown>'
    [288, 297) 'responseMsg' (line 815) <== Memory access at offset 297 overflows this variable
    [320, 336) 'gtest_ar' (line 822)
    [352, 368) 'gtest_ar' (line 847)
HINT: this may be a false positive if your program uses some custom stack unwind mechanism, swapcontext or vfork
      (longjmp and C++ exceptions *are* supported)
SUMMARY: AddressSanitizer: stack-buffer-overflow ../src/msgbuf/../msgbuf.h:129 in pldm_msgbuf_extract_uint8
Shadow bytes around the buggy address:
  0x200ff8305fc0: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
  0x200ff8305fd0: 00 00 00 00 00 00 00 00 00 00 00 00 f1 f1 f1 f1
  0x200ff8305fe0: 00 00 f3 f3 00 00 00 00 00 00 00 00 00 00 00 00
  0x200ff8305ff0: 00 00 f1 f1 f1 f1 f1 f1 01 f2 01 f2 04 f2 f8 f2
  0x200ff8306000: 04 f2 04 f2 04 f2 00 f2 f2 f2 00 f2 f2 f2 00 f2
=>0x200ff8306010: f2 f2 00 f2 f2 f2 00[01]f2 f2 f8 f8 f2 f2 00 00
  0x200ff8306020: f3 f3 00 00 00 00 00 00 00 00 00 00 00 00 00 00
  0x200ff8306030: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
  0x200ff8306040: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
  0x200ff8306050: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
  0x200ff8306060: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
Shadow byte legend (one shadow byte represents 8 application bytes):
  Addressable:           00
  Partially addressable: 01 02 03 04 05 06 07
  Heap left redzone:       fa
  Freed heap region:       fd
  Stack left redzone:      f1
  Stack mid redzone:       f2
  Stack right redzone:     f3
  Stack after return:      f5
  Stack use after scope:   f8
  Global redzone:          f9
  Global init order:       f6
  Poisoned by user:        f7
  Container overflow:      fc
  Array cookie:            ac
  Intra object redzone:    bb
  ASan internal:           fe
  Left alloca redzone:     ca
  Right alloca redzone:    cb
==297936==ABORTING
```

Signed-off-by: Andrew Jeffery <andrew@aj.id.au>
Change-Id: Ib63254bd345d28924aee47eb230bcbea0c88811a
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@amboar