From 6dda81f4384b94930826eded254d8c16f89a9248 Mon Sep 17 00:00:00 2001
From: Oleg Nesterov <oleg@redhat.com>
Date: Thu, 2 Apr 2009 16:58:35 -0700
Subject: [PATCH] pids: document task_pgrp/task_session is not safe without
tasklist/rcu
Even if task == current, it is not safe to dereference the result of
task_pgrp/task_session. We can race with another thread which changes the
special pid via setpgid/setsid.
Document this. The next 2 patches give an example of the unsafe usage, we
have more bad users.
[akpm@linux-foundation.org: coding-style fixes]
Signed-off-by: Oleg Nesterov <oleg@redhat.com>
Cc: Louis Rilling <Louis.Rilling@kerlabs.com>
Cc: "Eric W. Biederman" <ebiederm@xmission.com>
Cc: Pavel Emelyanov <xemul@openvz.org>
Cc: Sukadev Bhattiprolu <sukadev@linux.vnet.ibm.com>
Cc: Roland McGrath <roland@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
---
include/linux/sched.h | 5 +++++
1 file changed, 5 insertions(+)
diff --git a/include/linux/sched.h b/include/linux/sched.h
index b47c94e7560b..722dd313bf8a 100644
--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -1489,6 +1489,11 @@ static inline struct pid *task_tgid(struct task_struct *task)
return task->group_leader->pids[PIDTYPE_PID].pid;
}
+/*
+ * Without tasklist or rcu lock it is not safe to dereference
+ * the result of task_pgrp/task_session even if task == current,
+ * we can race with another thread doing sys_setsid/sys_setpgid.
+ */
static inline struct pid *task_pgrp(struct task_struct *task)
{
return task->group_leader->pids[PIDTYPE_PGID].pid;
--
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