On Fri, 2018-11-30 at 14:40 +0100, Florian Weimer wrote: > * Jürg Billeter: > > > This introduces a new thread group flag that can be set by calling > > > > prctl(PR_SET_KILL_DESCENDANTS_ON_EXIT, 1, 0, 0, 0) > > > > When a thread group exits with this flag set, it will send SIGKILL to > > all descendant processes. This can be used to prevent stray child > > processes. > > > > This flag is cleared on privilege gaining execve(2) to ensure an > > unprivileged process cannot get a privileged process to send SIGKILL. > > So this is inherited across regular execve? I'm not sure that's a good > idea. Yes, this matches PR_SET_CHILD_SUBREAPER (and other process attributes). Besides consistency and allowing a parent to configure the flag for a spawned process, this is also needed to prevent a process from clearing the flag (in combination with a seccomp filter). > > > Descendants that are orphaned and reparented to an ancestor of the > > current process before the current process exits, will not be killed. > > PR_SET_CHILD_SUBREAPER can be used to contain orphaned processes. > > For double- or triple-forking daemons, the reparenting will be racy, if > I understand things correctly. Can you please elaborate, if you're concerned about a particular race? As the commit message mentions, for containment this flag can be combined with PR_SET_CHILD_SUBREAPER (and PR_SET_NO_NEW_PRIVS). Jürg
