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

To: Oleg Nesterov <oleg@redhat.com>
Subject: Re: [PATCH -v2] Audit: push audit success and retcode into arch ptrace.h
From: Eric Paris <eparis@redhat.com>
Date: Tue, 07 Jun 2011 14:53:11 -0400
Cc: linux-kernel@vger.kernel.org, tony.luck@intel.com, fenghua.yu@intel.com, monstr@monstr.eu, ralf@linux-mips.org, benh@kernel.crashing.org, paulus@samba.org, schwidefsky@de.ibm.com, heiko.carstens@de.ibm.com, linux390@de.ibm.com, lethal@linux-sh.org, davem@davemloft.net, jdike@addtoit.com, richard@nod.at, tglx@linutronix.de, mingo@redhat.com, hpa@zytor.com, x86@kernel.org, viro@zeniv.linux.org.uk, akpm@linux-foundation.org, linux-ia64@vger.kernel.org, microblaze-uclinux@itee.uq.edu.au, linux-mips@linux-mips.org, linuxppc-dev@lists.ozlabs.org, linux-s390@vger.kernel.org, linux-sh@vger.kernel.org, sparclinux@vger.kernel.org, user-mode-linux-devel@lists.sourceforge.net
In-reply-to: <20110607171952.GA25729@redhat.com>
References: <20110603220451.23134.47368.stgit@paris.rdu.redhat.com> <20110607171952.GA25729@redhat.com>
Sender: linux-mips-bounce@linux-mips.org
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


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