Re: [PATCH -v2] Audit: push audit success and retcode into arch ptrace.h

Eric Paris
2011-06-07T18:53:11Z

On Tue, 2011-06-07 at 19:19 +0200, Oleg Nesterov wrote:
> On 06/03, Eric Paris wrote:
> >
> > The audit system previously expected arches calling to audit_syscall_exit to
> > supply as arguments if the syscall was a success and what the return code was.
> > Audit also provides a helper AUDITSC_RESULT which was supposed to simplify things
> > by converting from negative retcodes to an audit internal magic value stating
> > success or failure. This helper was wrong and could indicate that a valid
> > pointer returned to userspace was a failed syscall. The fix is to fix the
> > layering foolishness. We now pass audit_syscall_exit a struct pt_reg and it
> > in turns calls back into arch code to collect the return value and to
> > determine if the syscall was a success or failure. We also define a generic
> > is_syscall_success() macro which determines success/failure based on if the
> > value is < -MAX_ERRNO. This works for arches like x86 which do not use a
> > separate mechanism to indicate syscall failure.
>
> I know nothing about audit, but the patch looks fine to me.
>
>
> But I have a bit off-topic question,
>
> > diff --git a/arch/x86/kernel/entry_64.S b/arch/x86/kernel/entry_64.S
> > index 8a445a0..b7b1f88 100644
> > --- a/arch/x86/kernel/entry_64.S
> > +++ b/arch/x86/kernel/entry_64.S
> > @@ -53,6 +53,7 @@
> > #include <asm/paravirt.h>
> > #include <asm/ftrace.h>
> > #include <asm/percpu.h>
> > +#include <linux/err.h>
> >
> > /* Avoid __ASSEMBLER__'ifying <linux/audit.h> just for this. */
> > #include <linux/elf-em.h>
> > @@ -564,17 +565,16 @@ auditsys:
> > jmp system_call_fastpath
> >
> > /*
> > - * Return fast path for syscall audit. Call audit_syscall_exit()
> > + * Return fast path for syscall audit. Call __audit_syscall_exit()
> > * directly and then jump back to the fast path with TIF_SYSCALL_AUDIT
> > * masked off.
> > */
> > sysret_audit:
> > movq RAX-ARGOFFSET(%rsp),%rsi /* second arg, syscall return value */
> > - cmpq $0,%rsi /* is it < 0? */
> > - setl %al /* 1 if so, 0 if not */
> > + cmpq $-MAX_ERRNO,%rsi /* is it < -MAX_ERRNO? */
> > + setbe %al /* 1 if so, 0 if not */
> > movzbl %al,%edi /* zero-extend that into %edi */
> > - inc %edi /* first arg, 0->1(AUDITSC_SUCCESS), 1->2(AUDITSC_FAILURE) */
> > - call audit_syscall_exit
> > + call __audit_syscall_exit
>
> With or without this patch, can't we call audit_syscall_exit() twice
> if there is something else in _TIF_WORK_SYSCALL_EXIT mask apart from
> SYSCALL_AUDIT ? First time it is called from asm, then from
> syscall_trace_leave(), no?
>
> For example. The task has TIF_SYSCALL_AUDIT and nothing else, it does
> system_call->auditsys->system_call_fastpath. What if it gets, say,
> TIF_SYSCALL_TRACE before ret_from_sys_call?

No harm is done calling twice. The first call will do the real work and
cleanup. It will set a flag in the audit data that the work has been
done (in_syscall == 0) thus the second call will then not do any real
work and won't have anything to clean up.

-Eric