[lttng-dev] Problem with application changing UID

[Jonathan Rajotte-Julien]

On Tue, Sep 24, 2019 at 02:32:41PM +0000, Kramer, Zach wrote:
> Hi,
> 
> Is LTTng intended to support userspace applications that change their UID at run-time? As in, is there an expected behavior for when this happens?
> 
> For example:
> 
>   1.  Embedded device boots
>   2.  My daemon is launched as root via systemd
>   3.  Runs privileged code
>   4.  Changes UID to a less privileged user (500)
>   5.  Creates LTTng session
>      *   If session already exists, destroy it first
>   6.  <if ‘systemctl stop’ is called>: Destroy session
>      *   Otherwise it will be destroyed next daemon launch in step 5

When in this chain of operations is lttng-sessiond started?

> 
> [cid:image001.png at 01D56F9D.AF158770]
> The logs are cleared when ‘lttng destroy sess’ is called via the LTTng C-API. From my understanding, this should not happen.

I would tend to agree with you here. Would you be able to provide a small
reproducer for this? What is the version of lttng-*

-- 
Jonathan Rajotte-Julien
EfficiOS