[PATCH] weston-launch: only drop privileges when uid/gid != euid/egid

[Kristian Høgsberg]

On Tue, Aug 06, 2013 at 03:09:10PM +1000, Peter Hutterer wrote:
> initgroups requires CAP_SETGID and may fail. If we're not actually
> changing anything anyway we can just skip this and (most likely) fail later
> when we don't have the required permissions to open something.
> ---
> Should arguably be part of the previous patch but since it changes behaviour
> from before 636156d, here it is separately.
> 
> running weston-launch as user (w/o suid bit set) now passes this bit (and
> fails later, but still :)

weston-launch has to run as setuid root so drop_privileges() shouldn't
fail, unless you're running as non-setuid as a regular user.  Is this
just about getting a clearer error message and should we just go with
Armins patch instead then?

Kristian

>  src/weston-launch.c | 3 ++-
>  1 file changed, 2 insertions(+), 1 deletion(-)
> 
> diff --git a/src/weston-launch.c b/src/weston-launch.c
> index 5b03094..06194a9 100644
> --- a/src/weston-launch.c
> +++ b/src/weston-launch.c
> @@ -554,7 +554,8 @@ launch_compositor(struct weston_launch *wl, int argc, char *argv[])
>  	if (wl->new_user)
>  		setup_session(wl);
>  
> -	drop_privileges(wl);
> +	if (getuid() != geteuid() || getgid() != getegid())
> +		drop_privileges(wl);
>  
>  	if (wl->tty != STDIN_FILENO)
>  		setenv_fd("WESTON_TTY_FD", wl->tty);
> -- 
> 1.8.2.1
> 
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