From 24336eaeecea860b2a82530e07c80bc7e0558b73 Mon Sep 17 00:00:00 2001
From: Oleg Nesterov <oleg@tv-sign.ru>
Date: Wed, 30 Apr 2008 00:54:26 -0700
Subject: [PATCH] pids: introduce change_pid() helper
Based on Eric W. Biederman's idea.
Without tasklist_lock held task_session()/task_pgrp() can return NULL if the
caller races with setprgp()/setsid() which does detach_pid() + attach_pid().
This can happen even if task == current.
Intoduce the new helper, change_pid(), which should be used instead. This way
the caller always sees the special pid != NULL, either old or new.
Also change the prototype of attach_pid(), it always returns 0 and nobody
check the returned value.
Signed-off-by: Oleg Nesterov <oleg@tv-sign.ru>
Cc: "Eric W. Biederman" <ebiederm@xmission.com>
Cc: Pavel Emelyanov <xemul@openvz.org>
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/pid.h | 6 ++++--
kernel/pid.c | 21 ++++++++++++++++-----
2 files changed, 20 insertions(+), 7 deletions(-)
diff --git a/include/linux/pid.h b/include/linux/pid.h
index c7980810eb09..8d199033c0ca 100644
--- a/include/linux/pid.h
+++ b/include/linux/pid.h
@@ -89,9 +89,11 @@ extern struct pid *get_task_pid(struct task_struct *task, enum pid_type type);
* attach_pid() and detach_pid() must be called with the tasklist_lock
* write-held.
*/
-extern int attach_pid(struct task_struct *task, enum pid_type type,
- struct pid *pid);
+extern void attach_pid(struct task_struct *task, enum pid_type type,
+ struct pid *pid);
extern void detach_pid(struct task_struct *task, enum pid_type);
+extern void change_pid(struct task_struct *task, enum pid_type,
+ struct pid *pid);
extern void transfer_pid(struct task_struct *old, struct task_struct *new,
enum pid_type);
diff --git a/kernel/pid.c b/kernel/pid.c
index e9a31d362b28..20d59fa2d493 100644
--- a/kernel/pid.c
+++ b/kernel/pid.c
@@ -317,7 +317,7 @@ EXPORT_SYMBOL_GPL(find_pid);
/*
* attach_pid() must be called with the tasklist_lock write-held.
*/
-int attach_pid(struct task_struct *task, enum pid_type type,
+void attach_pid(struct task_struct *task, enum pid_type type,
struct pid *pid)
{
struct pid_link *link;
@@ -325,11 +325,10 @@ int attach_pid(struct task_struct *task, enum pid_type type,
link = &task->pids[type];
link->pid = pid;
hlist_add_head_rcu(&link->node, &pid->tasks[type]);
-
- return 0;
}
-void detach_pid(struct task_struct *task, enum pid_type type)
+static void __change_pid(struct task_struct *task, enum pid_type type,
+ struct pid *new)
{
struct pid_link *link;
struct pid *pid;
@@ -339,7 +338,7 @@ void detach_pid(struct task_struct *task, enum pid_type type)
pid = link->pid;
hlist_del_rcu(&link->node);
- link->pid = NULL;
+ link->pid = new;
for (tmp = PIDTYPE_MAX; --tmp >= 0; )
if (!hlist_empty(&pid->tasks[tmp]))
@@ -348,6 +347,18 @@ void detach_pid(struct task_struct *task, enum pid_type type)
free_pid(pid);
}
+void detach_pid(struct task_struct *task, enum pid_type type)
+{
+ __change_pid(task, type, NULL);
+}
+
+void change_pid(struct task_struct *task, enum pid_type type,
+ struct pid *pid)
+{
+ __change_pid(task, type, pid);
+ attach_pid(task, type, pid);
+}
+
/* transfer_pid is an optimization of attach_pid(new), detach_pid(old) */
void transfer_pid(struct task_struct *old, struct task_struct *new,
enum pid_type type)
--
GitLab