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authorOleg Nesterov <oleg@redhat.com>2009-04-02 16:58:35 -0700
committerLinus Torvalds <torvalds@linux-foundation.org>2009-04-02 19:05:02 -0700
commit6dda81f4384b94930826eded254d8c16f89a9248 (patch)
treea7b27ca16a6feba637cb01e68b54c58b6ca07bc2
parent8e654fba4a376f436bdfe361fc5cdbc87ac09b35 (diff)
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>
-rw-r--r--include/linux/sched.h5
1 files changed, 5 insertions, 0 deletions
diff --git a/include/linux/sched.h b/include/linux/sched.h
index b47c94e7560..722dd313bf8 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;