Re: [PATCH v2 3/3] audit: Use syscall_get_return_value to get syscall return code in audit_syscall_exit

[Paul Moore <paul@paul-moore.com>]

On Wed, May 12, 2021 at 4:43 AM He Zhe <zhe.he@windriver.com> wrote:
> On 5/11/21 10:51 PM, Paul Moore wrote:
> > On Mon, May 10, 2021 at 11:19 PM He Zhe <zhe.he@windriver.com> wrote:
> >> On 5/11/21 6:38 AM, Paul Moore wrote:
> >>> On Fri, Apr 23, 2021 at 6:36 AM He Zhe <zhe.he@windriver.com> wrote:
> >>>> regs_return_value for some architectures like arm64 simply retrieve
> >>>> register value from pt_regs without sign extension in 32-bit compatible
> >>>> case and cause audit to have false syscall return code. For example,
> >>>> 32-bit -13 would be treated as 4294967283 below.
> >>>>
> >>>> type=SYSCALL msg=audit(1611110715.887:582): arch=40000028 syscall=322
> >>>> success=yes exit=4294967283
> >>>>
> >>>> We just added proper sign extension in syscall_get_return_value which
> >>>> should be used instead.
> >>>>
> >>>> Signed-off-by: He Zhe <zhe.he@windriver.com>
> >>>> ---
> >>>> v1 to v2: No change
> >>>>
> >>>>  include/linux/audit.h | 2 +-
> >>>>  1 file changed, 1 insertion(+), 1 deletion(-)
> >>> Perhaps I missed it but did you address the compile error that was
> >>> found by the kernel test robot?
> >> I sent a patch adding syscall_get_return_value for alpha to fix this bot warning.
> >> https://lore.kernel.org/lkml/20210426091629.45020-1-zhe.he@windriver.com/
> >> which can be found in this mail thread.
> > At the very least you should respin the patchset with the alpha fix
> > included in the patchset; it's a bit messy otherwise.
> >
> >>>> diff --git a/include/linux/audit.h b/include/linux/audit.h
> >>>> index 82b7c1116a85..135adbe22c19 100644
> >>>> --- a/include/linux/audit.h
> >>>> +++ b/include/linux/audit.h
> >>>> @@ -334,7 +334,7 @@ static inline void audit_syscall_exit(void *pt_regs)
> >>>>  {
> >>>>         if (unlikely(audit_context())) {
> >>>>                 int success = is_syscall_success(pt_regs);
> >>> Since we are shifting to use syscall_get_return_value() below, would
> >>> it also make sense to shift to using syscall_get_error() here instead
> >>> of is_syscall_success()?
> >> In [PATCH v2 1/3], is_syscall_success calls syscall_get_return_value to take
> >> care of the sign extension issue. Keeping using is_syscall_success is to not
> >> potentially changing other architectures' behavior.
> > That was only for aarch64, right?  What about all the other
> > architectures?  The comment block for syscall_get_return_value()
> > advises that syscall_get_error() should be used and that appears to be
> > what is done in the ptrace code.
>
> Yes, it was only for aarch64. No similar issue hasn't observed for other
> architectures on my side, so I was trying to minimize the impact.
>
> The "comment block" you mentioned is the following line, right?
> https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/include/asm-generic/syscall.h#n77
> [PATCH v2 2/3] was used to cover this concern. But as we can see in
> Mark Rutland's last reply, there'are more things to be considered and we are
> still trying to find a proper solution.

It sounds like you are going to be submitting another patchset at some
point in the future - that's good - when you do please use
syscall_get_error() in conjunction with syscall_get_return_value() or
explain why doing so is wrong.  The explanation should be in a code
comment, not just an email and/or commit description.

-- 
paul moore
www.paul-moore.com