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

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Message-ID: <6f1262fc-21ad-f872-5460-e78d4685c9c4@sony.com>
Date:   Thu, 30 Jul 2020 17:31:17 +0200
From:   peter enderborg <peter.enderborg@...y.com>
To:     Steven Rostedt <rostedt@...dmis.org>
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 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.
>
>> +                 ),
>> +
>> +        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"


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