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exit: fix the setns() && PR_SET_CHILD_SUBREAPER interaction

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find_new_reaper() checks same_thread_group(reaper, child_reaper) to
prevent the cross-namespace reparenting but this is not enough if the
exiting parent was injected by setns() + fork().

Suppose we have a process P in the root namespace and some namespace X.
P does setns() to enter the X namespace, and forks the child C.
C forks a grandchild G and exits.

The grandchild G should be re-parented to X->child_reaper, but in this
case the ->real_parent chain does not lead to ->child_reaper, so it will
be wrongly reparanted to P's sub-reaper or a global init.

Signed-off-by: Oleg Nesterov <oleg@redhat.com>
Signed-off-by: Eric W. Biederman <ebiederm@xmission.com>
This commit is contained in:
Oleg Nesterov 2017-01-30 19:17:35 +01:00 committed by Eric W. Biederman
parent 1328c72700
commit c6c70f4455
1 changed files with 8 additions and 5 deletions
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13
kernel/exit.c
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@ -578,15 +578,18 @@ static struct task_struct *find_new_reaper(struct task_struct *father,
return thread;
if (father->signal->has_child_subreaper) {
unsigned int ns_level = task_pid(father)->level;
/*
* Find the first ->is_child_subreaper ancestor in our pid_ns.
* We start from father to ensure we can not look into another
* namespace, this is safe because all its threads are dead.
* We can't check reaper != child_reaper to ensure we do not
* cross the namespaces, the exiting parent could be injected
* by setns() + fork().
* We check pid->level, this is slightly more efficient than
* task_active_pid_ns(reaper) != task_active_pid_ns(father).
*/
for (reaper = father;
!same_thread_group(reaper, child_reaper);
for (reaper = father->real_parent;
task_pid(reaper)->level == ns_level;
reaper = reaper->real_parent) {
/* call_usermodehelper() descendants need this check */
if (reaper == &init_task)
break;
if (!reaper->signal->is_child_subreaper)