[lttng-dev] [PATCH lttng-ust v2] Add setuid wrappers for per-UID buffers

Philippe Proulx eeppeliteloop at gmail.com
Sun Jun 9 12:08:24 EDT 2019

On Wed, Jun 5, 2019 at 2:57 PM Gabriel-Andrew Pollo-Guilbert
<gabriel.pollo-guilbert at efficios.com> wrote:
> diff --git a/doc/man/lttng-ust.3.txt b/doc/man/lttng-ust.3.txt
> index 5c9c9f5d..d58b43c7 100644
> --- a/doc/man/lttng-ust.3.txt
> +++ b/doc/man/lttng-ust.3.txt
> @@ -744,6 +744,17 @@ library before you start the application. Typical use cases include
>  daemons closing all file descriptors after man:fork(2), and buggy
>  applications doing ``double-closes''.

A few documentation fixes:

> +Using LTTng-UST with applications that change user

... that change the effective user ID

> +~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
> +If your application is traced using per-UID buffers and changes user ID using

If LTTng traces your application using per-UID buffers (see the
nloption:--buffers-uid option of man:lttng-enable-channel(1)) and
changes the process's effective user ID with

> +man:setuid(2), the library `liblttng-ust-setuid.so` needs to be preloaded
> +before starting the application with the `LD_PRELOAD` environment variable (see
> +man:ld.so(8)). This way, events generated after the UID change will be forwarded

... event records generated after the user ID change are forwarded ...

> +to the correct buffer.
> +
> +This workaround requires that the tracing session be global (root
> +lttng-sessiond) in order to avoid permission problems between a session

... be global (created by a root session daemon; see man:lttng-sessiond(1))
to avoid permission problems of a session

> +daemon started by another user.


> --
> 2.21.0
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