* [PATCH 1/3] pids: document task_pgrp/task_session is not safe without tasklist/rcu
@ 2009-01-16 5:55 Oleg Nesterov
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From: Oleg Nesterov @ 2009-01-16 5:55 UTC (permalink / raw)
To: Andrew Morton
Cc: Eric W. Biederman, Pavel Emelyanov, Sukadev Bhattiprolu,
linux-kernel
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.
Signed-off-by: Oleg Nesterov <oleg@redhat.com>
--- CUR/include/linux/sched.h~SP_1_COMMENT 2009-01-12 23:07:48.000000000 +0100
+++ CUR/include/linux/sched.h 2009-01-16 02:13:50.000000000 +0100
@@ -1449,6 +1449,13 @@ static inline struct pid *task_tgid(stru
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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2009-01-16 5:55 [PATCH 1/3] pids: document task_pgrp/task_session is not safe without tasklist/rcu Oleg Nesterov
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