The patch titled
pids: document task_pgrp/task_session is not safe without tasklist/rcu
has been added to the -mm tree. Its filename is
pids-document-task_pgrp-task_session-is-not-safe-without-tasklist-rcu.patch
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------------------------------------------------------
Subject: pids: document task_pgrp/task_session is not safe without tasklist/rcu
From: Oleg Nesterov <oleg@xxxxxxxxxx>
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@xxxxxxxxxx>
Cc: Louis Rilling <Louis.Rilling@xxxxxxxxxxx>
Cc: "Eric W. Biederman" <ebiederm@xxxxxxxxxxxx>
Cc: Pavel Emelyanov <xemul@xxxxxxxxxx>
Cc: Sukadev Bhattiprolu <sukadev@xxxxxxxxxxxxxxxxxx>
Cc: Roland McGrath <roland@xxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
include/linux/sched.h | 7 +++++++
1 file changed, 7 insertions(+)
diff -puN include/linux/sched.h~pids-document-task_pgrp-task_session-is-not-safe-without-tasklist-rcu include/linux/sched.h
--- a/include/linux/sched.h~pids-document-task_pgrp-task_session-is-not-safe-without-tasklist-rcu
+++ a/include/linux/sched.h
@@ -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;
_
Patches currently in -mm which might be from oleg@xxxxxxxxxx are
getrusage-fill-ru_maxrss-value.patch
pids-document-task_pgrp-task_session-is-not-safe-without-tasklist-rcu.patch
pids-document-task_pgrp-task_session-is-not-safe-without-tasklist-rcu-fix.patch
pids-improve-get_task_pid-to-fix-the-unsafe-sys_wait4-task_pgrp.patch
pids-refactor-vnr-nr_ns-helpers-to-make-them-safe.patch
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