[LTP] [PATCH v2 0/3] safe_macros: Fix undefined behaviour in vararg handling

[Tudor Cretu]

On 29-11-2022 13:59, Petr Vorel wrote:
> Hi all,
> 
>> Hello,
> 
>> So I'm happy with this, but I think Cyril's comment deserves a response:

Indeed, I noticed it too late after sending the v2.

> +1
> 
>>> Looking at how glibc handles this, the code looks like:
> 
>>> 	int mode = 0;
> 
>>> 	if (__OPEN_NEEDS_MODE(oflag)) {
>>> 		..
>>> 		mode = va_arg(arg, int);
>>> 		..
>>> 	}
> 
>>> That sounds much easier than messing with the macros and should avoid
>>> undefined behavior.

I considered this and I think it's better to focus strictly on the 
handling the variadicness issue, and wanted to avoid duplicating logic 
from libcs.

> +1
> 
>> I don't see why, __OPEN_NEEDS_MODE is going to be different between
> 
>> functions and libc/kernel versions.

Haven't thought about that, that's a good point in my opinion.

> 
> Looking at glibc's __OPEN_NEEDS_MODE definition, the logic is obviously the same
> as musl code for open (it just use O_TMPFILE instead of __O_TMPFILE therefore no
> need to check for #ifdef __O_TMPFILE).

I agree, for open/openat this approach would be fairly simple, there is 
semctl too though, I'll need to have a look how glibc and musl handle it.

Kind regards,
Tudor

> 
> Kind regards,
> Petr
> 
>> Reviewed-by: Richard Palethorpe <rpalethorpe@suse.com>
> 
>> Tudor Cretu <tudor.cretu@arm.com> writes:
> 
>>> Accessing elements in an empty va_list results in undefined behaviour[0]
>>> that can include accessing arbitrary stack memory. While typically this
>>> doesn't raise a fault, some new more security-oriented architectures
>>> (e.g. CHERI[1] or Morello[2]) don't allow it.
> 
>>> Therefore, remove the variadicness from safe_* wrappers that always call
>>> the functions with the optional argument included.
> 
>>> Adapt the respective SAFE_* macros to handle the change by passing a
>>> default argument if they're omitted.
> 
>>> [0]: [ISO/IEC 9899:2011] Programming Languages—C, 3rd ed, paragraph 7.16.1.1
>>> [1]: https://www.cl.cam.ac.uk/research/security/ctsrd/cheri/
>>> [2]: https://www.morello-project.org/
> 
>>> v2..v1:
>>>    - PATCH 1: Remove the NULL argument for mode from SAFE_OPEN instances
>>>      to avoid the pointer to int conversion.
> 
>>> Tudor Cretu (3):
>>>    safe_open: Fix undefined behaviour in vararg handling
>>>    safe_openat: Fix undefined behaviour in vararg handling
>>>    safe_semctl: Fix undefined behaviour in vararg handling
> 
>>>   include/old/safe_macros.h                         |  6 ++++--
>>>   include/safe_macros_fn.h                          |  3 ++-
>>>   include/tst_safe_file_at.h                        | 10 ++++++----
>>>   include/tst_safe_macros.h                         |  6 ++++--
>>>   include/tst_safe_sysv_ipc.h                       | 14 +++++++++-----
>>>   lib/safe_macros.c                                 | 13 +------------
>>>   lib/tst_cgroup.c                                  |  2 +-
>>>   lib/tst_safe_file_at.c                            | 11 +++--------
>>>   lib/tst_safe_sysv_ipc.c                           | 10 +---------
>>>   testcases/kernel/syscalls/fgetxattr/fgetxattr01.c |  2 +-
>>>   testcases/kernel/syscalls/fgetxattr/fgetxattr02.c |  2 +-
>>>   testcases/kernel/syscalls/fgetxattr/fgetxattr03.c |  2 +-
>>>   testcases/kernel/syscalls/fsetxattr/fsetxattr01.c |  2 +-
>>>   testcases/kernel/syscalls/fsetxattr/fsetxattr02.c |  2 +-
>>>   14 files changed, 36 insertions(+), 49 deletions(-)
> 
>>> -- 
>>> 2.25.1