kernel/exit.c: release ptraced tasks before zap_pid_ns_processes (8fb335e0) · Commits · 戴 / test

Currently, exit_ptrace() adds all ptraced tasks in a dead list, then zap_pid_ns_processes() waits on all tasks in a current pidns, and only then are tasks from the dead list released. zap_pid_ns_processes() can get stuck on waiting tasks from the dead list. In this case, we will have one unkillable process with one or more dead children. Thanks to Oleg for the advice to release tasks in find_child_reaper(). Link: http://lkml.kernel.org/r/20190110175200.12442-1-avagin@gmail.com Fixes: ("exit: ptrace: shift "reap dead" code from exit_ptrace() to forget_original_parent()") Signed-off-by:

Andrei Vagin <avagin@gmail.com> Signed-off-by:

Oleg Nesterov <oleg@redhat.com> Cc: "Eric W. Biederman" <ebiederm@xmission.com> Cc: <stable@vger.kernel.org> Signed-off-by:

Andrew Morton <akpm@linux-foundation.org> Signed-off-by:

Linus Torvalds <torvalds@linux-foundation.org>

kernel/exit.c

+10 −2

Original line number	Diff line number	Diff line
		@@ -558,12 +558,14 @@ static struct task_struct find_alive_thread(struct task_struct p)
		return NULL;
		}

		static struct task_struct find_child_reaper(struct task_struct father)
		static struct task_struct find_child_reaper(struct task_struct father,
		struct list_head *dead)
		__releases(&tasklist_lock)
		__acquires(&tasklist_lock)
		{
		struct pid_namespace *pid_ns = task_active_pid_ns(father);
		struct task_struct *reaper = pid_ns->child_reaper;
		struct task_struct p, n;

		if (likely(reaper != father))
		return reaper;
		@@ -579,6 +581,12 @@ static struct task_struct find_child_reaper(struct task_struct father)
		panic("Attempted to kill init! exitcode=0x%08x\n",
		father->signal->group_exit_code ?: father->exit_code);
		}

		list_for_each_entry_safe(p, n, dead, ptrace_entry) {
		list_del_init(&p->ptrace_entry);
		release_task(p);
		}

		zap_pid_ns_processes(pid_ns);
		write_lock_irq(&tasklist_lock);

		@@ -668,7 +676,7 @@ static void forget_original_parent(struct task_struct *father,
		exit_ptrace(father, dead);

		/* Can drop and reacquire tasklist_lock */
		reaper = find_child_reaper(father);
		reaper = find_child_reaper(father, dead);
		if (list_empty(&father->children))
		return;

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