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authorOleg Nesterov <oleg@tv-sign.ru>2008-04-30 00:54:26 -0700
committerLinus Torvalds <torvalds@linux-foundation.org>2008-04-30 08:29:48 -0700
commit24336eaeecea860b2a82530e07c80bc7e0558b73 (patch)
tree12a34660f732e12ba18262083c1a2eea5a824f6a
parent65450cebc6a2efde80ed45514f727e6e4dc1eafd (diff)
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>
-rw-r--r--include/linux/pid.h6
-rw-r--r--kernel/pid.c21
2 files changed, 20 insertions, 7 deletions
diff --git a/include/linux/pid.h b/include/linux/pid.h
index c7980810eb0..8d199033c0c 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 e9a31d362b2..20d59fa2d49 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)