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author | Oleg Nesterov <oleg@redhat.com> | 2014-12-10 15:55:02 -0800 |
---|---|---|
committer | Linus Torvalds <torvalds@linux-foundation.org> | 2014-12-10 17:41:17 -0800 |
commit | 7d24e2df52f596a1ea922e4f84a61f2fb24fbb70 (patch) | |
tree | 45f2b9d7af1852338c9e0db11107c504f3dfcf31 | |
parent | 8a1296aea4a319b33c3367ff3805835e949a229f (diff) | |
download | op-kernel-dev-7d24e2df52f596a1ea922e4f84a61f2fb24fbb70.zip op-kernel-dev-7d24e2df52f596a1ea922e4f84a61f2fb24fbb70.tar.gz |
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@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>
-rw-r--r-- | kernel/exit.c | 6 |
1 files changed, 4 insertions, 2 deletions
diff --git a/kernel/exit.c b/kernel/exit.c index fd38a8f..9babd47 100644 --- a/kernel/exit.c +++ b/kernel/exit.c @@ -492,7 +492,9 @@ static struct task_struct *find_new_reaper(struct task_struct *father) 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; /* @@ -502,7 +504,7 @@ static struct task_struct *find_new_reaper(struct task_struct *father) * 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)) |