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Subject[PATCH 1/2] exec: Don't set group_exit_task during a coredump

Instead test SIGNAL_GROUP_COREDUMP in signal_group_exit(). This
results in clearer easier to understand logic. This makes the code
easier to modify in the future as this leaves de_thread as the only
user of group_exit_task.

This is safe because there are only two places that set
SIGNAL_GROUP_COREDUMP. In one place the code is setting
SIGNAL_GROUP_EXIT and SIGNAL_GROUP_COREDUMP together with the result
that signal_group_exit() will subsequently return true. In the other
the location which is being changed SIGNAL_GROUP_COREDUMP is being set
along with signal_group_exit, which also causes subsequent calls of
signal_group_exit to return true.

Thus testing SIGNAL_GROUP_COREDUMP in signal_group_exit() results
in no change in behavior.

Only signal_group_exit tests group_exit_task so leaving as NULL
during a coredump and nothing uses the value of group_exit_task
that the coredump sets. So not setting group_exit_task is
safe during a coredump.

I looked at the commit that introduced this behavior[1] and Oleg
describes that he was setting group_exit_task simply to cause
signal_group_exit to return true. So no surprises come from the
history.

Cc: Oleg Nesterov <oleg@redhat.com>
[1] 6cd8f0acae34 ("coredump: ensure that SIGKILL always kills the dumping thread")
Signed-off-by: "Eric W. Biederman" <ebiederm@xmission.com>
---
fs/coredump.c | 2 --
include/linux/sched/signal.h | 2 +-
2 files changed, 1 insertion(+), 3 deletions(-)

diff --git a/fs/coredump.c b/fs/coredump.c
index 7237f07ff6be..37b71c72ab3a 100644
--- a/fs/coredump.c
+++ b/fs/coredump.c
@@ -369,7 +369,6 @@ static int zap_threads(struct task_struct *tsk, struct mm_struct *mm,
spin_lock_irq(&tsk->sighand->siglock);
if (!signal_group_exit(tsk->signal)) {
mm->core_state = core_state;
- tsk->signal->group_exit_task = tsk;
nr = zap_process(tsk, exit_code, 0);
clear_tsk_thread_flag(tsk, TIF_SIGPENDING);
}
@@ -481,7 +480,6 @@ static void coredump_finish(struct mm_struct *mm, bool core_dumped)
spin_lock_irq(&current->sighand->siglock);
if (core_dumped && !__fatal_signal_pending(current))
current->signal->group_exit_code |= 0x80;
- current->signal->group_exit_task = NULL;
current->signal->flags = SIGNAL_GROUP_EXIT;
spin_unlock_irq(&current->sighand->siglock);

diff --git a/include/linux/sched/signal.h b/include/linux/sched/signal.h
index 0ee5e696c5d8..92c72f5db111 100644
--- a/include/linux/sched/signal.h
+++ b/include/linux/sched/signal.h
@@ -265,7 +265,7 @@ static inline void signal_set_stop_flags(struct signal_struct *sig,
/* If true, all threads except ->group_exit_task have pending SIGKILL */
static inline int signal_group_exit(const struct signal_struct *sig)
{
- return (sig->flags & SIGNAL_GROUP_EXIT) ||
+ return (sig->flags & (SIGNAL_GROUP_EXIT | SIGNAL_GROUP_COREDUMP)) ||
(sig->group_exit_task != NULL);
}

--
2.20.1
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