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Oleg Nesterov 7d24e2df52 exit: reparent: fix the cross-namespace PR_SET_CHILD_SUBREAPER reparenting ... find_new_reaper() assumes that "has_child_subreaper" logic is safe as long as we are not the exiting ->child_reaper and this is doubly wrong: 1. In fact it is safe if "pid_ns->child_reaper == father"; there must be no children after zap_pid_ns_processes() returns, so it doesn't matter what we return in this case and even pid_ns->child_reaper is wrong otherwise: we can't reparent to ->child_reaper == current. This is not a bug, but this is confusing. 2. It is not safe if we are not pid_ns->child_reaper but from the same thread group. We drop tasklist_lock before zap_pid_ns_processes(), so another thread can lock it and choose the new reaper from the upper namespace if has_child_subreaper == T, and this is obviously wrong. This is not that bad, zap_pid_ns_processes() won't return until the the new reaper reaps all zombies, but this should be fixed anyway. We could change for_each_thread() loop to use ->exit_state instead of PF_EXITING which we had to use until 8aac62706a, or we could change copy_signal() to check CLONE_NEWPID before setting has_child_subreaper, but lets change this code so that it is clear we can't look outside of our namespace, otherwise same_thread_group(reaper, child_reaper) check will look wrong and confusing anyway. We can simply start from "father" and fix the problem. We can't wrongly return a thread from the same thread group if ->is_child_subreaper == T, we know that all threads have PF_EXITING set. Signed-off-by: Oleg Nesterov <oleg@redhat.com> Cc: Aaron Tomlin <atomlin@redhat.com> Cc: "Eric W. Biederman" <ebiederm@xmission.com> Cc: Kay Sievers <kay@vrfy.org> Cc: Lennart Poettering <lennart@poettering.net> Cc: Sterling Alexander <stalexan@redhat.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>		2014-12-10 17:41:17 -08:00
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exit.c	exit: reparent: fix the cross-namespace PR_SET_CHILD_SUBREAPER reparenting	2014-12-10 17:41:17 -08:00
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