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

[Petr Vorel <pvorel@suse.cz>]

Hi all,

> Hello,

> So I'm happy with this, but I think Cyril's comment deserves a response:
+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.
+1

> I don't see why, __OPEN_NEEDS_MODE is going to be different between

> functions and libc/kernel versions.

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).

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

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