[lttng-dev] lttng enable-channel option for blocking

[Paul_Woegerer@mentor.com (Woegerer, Paul)]

On 04/27/2012 02:43 PM, Mathieu Desnoyers wrote:
> * Woegerer, Paul (Paul_Woegerer at mentor.com) wrote:
>> On 04/27/2012 01:33 PM, Mathieu Desnoyers wrote:
>>> A core difference between ulimit and user-space tracing is that ulimit
>>> can only be set within the environment (and access right) of the user
>>> running the application. System-wide tracing sessions can be initiated
>>> by users member of the "tracing" group -- giving them the ability to
>>> potentially DoS an application does not appear to me to be a good
>>> security practice. Thoughts ?
>> Hmm, how would that look in practice ? Lets assume there is the web
>> server which was started by an init-script in runlevel 3. How does a
>> user that belongs to group tracing hava a chance to DoS the already
>> running running web server. As far as I understand the trace session
>> concept every tracing user can only see (and affect) the tracing session
>> that he initiated. Even if the web server itself runs in a tracing
>> session (of user wwwrun) other tracing users wouldn't see it when they
>> do a "lttng list", right ?
> Let me clarify the concept of tracing session in lttng 2.0.
>
> We support launching per-user sessiond, which only interact with the
> user's applications. That's all fine with security.
>
> Now, we also support a root system-wide sessiond, which allows kernel
> and user-space tracing. The "tracing" group has every right to create a
> tracing session and trace the kernel and _all_ applications that were
> already or will be running on the system.

Ah, I see. I was not aware of the "... and _all_ applications that were 
already or will be running on the system" aspect of the concept. In that 
case I would rather invert the semantic in the API and instead of having 
a tracepoint() function that potentially blocks I would declare 
tracepoint() to never ever block and additionally provide tracepointb() 
that does potentially block.

--
Paul

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