linux-kernel - Re: [PATCH] RFC: selinux avc trace

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Date:   Thu, 30 Jul 2020 12:02:00 -0400
From:   Steven Rostedt <rostedt@...dmis.org>
To:     peter enderborg <peter.enderborg@...y.com>
Cc:     Thiébaud Weksteen <tweek@...gle.com>,
        Paul Moore <paul@...l-moore.com>,
        Nick Kralevich <nnk@...gle.com>,
        Joel Fernandes <joelaf@...gle.com>,
        Stephen Smalley <stephen.smalley.work@...il.com>,
        Eric Paris <eparis@...isplace.org>,
        Ingo Molnar <mingo@...hat.com>,
        Mauro Carvalho Chehab <mchehab+huawei@...nel.org>,
        "David S. Miller" <davem@...emloft.net>,
        Rob Herring <robh@...nel.org>, <linux-kernel@...r.kernel.org>,
        <selinux@...r.kernel.org>
Subject: Re: [PATCH] RFC: selinux avc trace

On Thu, 30 Jul 2020 17:31:17 +0200
peter enderborg <peter.enderborg@...y.com> wrote:

> On 7/30/20 5:04 PM, Steven Rostedt wrote:
> > On Thu, 30 Jul 2020 16:29:12 +0200
> > peter enderborg <peter.enderborg@...y.com> wrote:
> >  
> >> +#undef TRACE_SYSTEM
> >> +#define TRACE_SYSTEM avc
> >> +
> >> +#if !defined(_TRACE_AVC_H) || defined(TRACE_HEADER_MULTI_READ)
> >> +#define _TRACE_AVC_H
> >> +
> >> +#include <linux/tracepoint.h>
> >> +TRACE_EVENT(avc_data,
> >> +        TP_PROTO(u32 requested,
> >> +             u32 denied,
> >> +             u32 audited,
> >> +             int result,
> >> +             const char *msg
> >> +             ),
> >> +
> >> +        TP_ARGS(requested, denied, audited, result,msg),
> >> +
> >> +        TP_STRUCT__entry(
> >> +             __field(u32, requested)
> >> +             __field(u32, denied)
> >> +             __field(u32, audited)
> >> +             __field(int, result)
> >> +             __array(char, msg, 255)  
> > You want to use __string() here, otherwise you are wasting a lot of
> > buffer space.
> >
> > 		__string( msg, msg)  

> It should be a full structure with a lot of sub strings.  But that make is even more relevant.

So one event instance can have a list of strings recorded?

> >  
> >> +                 ),
> >> +
> >> +        TP_fast_assign(
> >> +               __entry->requested    = requested;
> >> +               __entry->denied    = denied;
> >> +               __entry->audited    = audited;
> >> +               __entry->result    = result;
> >> +               memcpy(__entry->msg, msg, 255);  
> > Not to mention, the above is a bug. As the msg being passed in, is
> > highly unlikely to be 255 bytes. You just leaked all that memory after
> > the sting to user space.
> >
> > Where you want here:
> >
> > 		__assign_str( msg, msg );  
> 
> Directly in to the code. Was more in to get in to discussion on how complex we should have
> the trace data. There is a lot of fields. Not all is always present. Is there any good way
> to handle that? Like "something= somethingelse=42" or "something=nil somthingelse=42"

Can you show what you want to record and what you want to display? I'm
not totally understanding the request.

-- Steve

> >> +    ),
> >> +
> >> +        TP_printk("requested=0x%x denied=%d audited=%d result=%d
> >> msg=%s",
> >> +              __entry->requested, __entry->denied, __entry->audited,
> >> __entry->result, __entry->msg
> >> +              )  
>