The patch titled
Subject: exit: reparent: fix the cross-namespace PR_SET_CHILD_SUBREAPER reparenting
has been added to the -mm tree. Its filename is
exit-reparent-fix-the-cross-namespace-pr_set_child_subreaper-reparenting.patch
This patch should soon appear at
http://ozlabs.org/~akpm/mmots/broken-out/exit-reparent-fix-the-cross-namespace-pr_set_child_subreaper-reparenting.patch
echo and later at
echo http://ozlabs.org/~akpm/mmotm/broken-out/exit-reparent-fix-the-cross-namespace-pr_set_child_subreaper-reparenting.patch
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------------------------------------------------------
From: Oleg Nesterov <oleg@xxxxxxxxxx>
Subject: 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 8aac62706ada, 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@xxxxxxxxxx>
Cc: Aaron Tomlin <atomlin@xxxxxxxxxx>
Cc: "Eric W. Biederman" <ebiederm@xxxxxxxxxxxx>
Cc: Kay Sievers <kay@xxxxxxxx>
Cc: Lennart Poettering <lennart@xxxxxxxxxxxxxx>
Cc: Sterling Alexander <stalexan@xxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
kernel/exit.c | 6 ++++--
1 file changed, 4 insertions(+), 2 deletions(-)
diff -puN kernel/exit.c~exit-reparent-fix-the-cross-namespace-pr_set_child_subreaper-reparenting kernel/exit.c
--- a/kernel/exit.c~exit-reparent-fix-the-cross-namespace-pr_set_child_subreaper-reparenting
+++ a/kernel/exit.c
@@ -495,7 +495,9 @@ static struct task_struct *find_new_reap
zap_pid_ns_processes(pid_ns);
write_lock_irq(&tasklist_lock);
- } else if (father->signal->has_child_subreaper) {
+ }
+
+ if (father->signal->has_child_subreaper) {
struct task_struct *reaper;
/*
@@ -505,7 +507,7 @@ static struct task_struct *find_new_reap
* PID namespace. However we still need the check above, see
* http://marc.info/?l=linux-kernel&m=131385460420380
*/
- for (reaper = father->real_parent;
+ for (reaper = father;
reaper != &init_task;
reaper = reaper->real_parent) {
if (same_thread_group(reaper, pid_ns->child_reaper))
_
Patches currently in -mm which might be from oleg@xxxxxxxxxx are
mmfs-introduce-helpers-around-the-i_mmap_mutex.patch
mm-use-new-helper-functions-around-the-i_mmap_mutex.patch
mm-convert-i_mmap_mutex-to-rwsem.patch
mm-rmap-share-the-i_mmap_rwsem.patch
uprobes-share-the-i_mmap_rwsem.patch
mm-xip-share-the-i_mmap_rwsem.patch
mm-memory-failure-share-the-i_mmap_rwsem.patch
mm-nommu-share-the-i_mmap_rwsem.patch
mm-memoryc-share-the-i_mmap_rwsem.patch
remove-unnecessary-is_valid_nodemask.patch
proc-task_state-read-cred-group_info-outside-of-task_lock.patch
proc-task_state-deuglify-the-max_fds-calculation.patch
proc-task_state-move-the-main-seq_printf-outside-of-rcu_read_lock.patch
proc-task_state-ptrace_parent-doesnt-need-pid_alive-check.patch
sched_show_task-fix-unsafe-usage-of-real_parent.patch
exit-reparent-use-ptrace_entry-rather-than-sibling-for-exit_dead-tasks.patch
exit-reparent-cleanup-the-changing-of-parent.patch
exit-reparent-cleanup-the-changing-of-parent-fix.patch
exit-reparent-cleanup-the-usage-of-reparent_leader.patch
exit-ptrace-shift-reap-dead-code-from-exit_ptrace-to-forget_original_parent.patch
usermodehelper-dont-use-clone_vfork-for-____call_usermodehelper.patch
usermodehelper-kill-the-kmod_thread_locker-logic.patch
exit-reparent-fix-the-dead-parent-pr_set_child_subreaper-reparenting.patch
exit-reparent-fix-the-cross-namespace-pr_set_child_subreaper-reparenting.patch
exit-reparent-s-while_each_thread-for_each_thread-in-find_new_reaper.patch
exit-reparent-document-the-has_child_subreaper-checks.patch
exit-reparent-introduce-find_child_reaper.patch
exit-reparent-introduce-find_alive_thread.patch
linux-next.patch
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