Commit 24336eae authored by Oleg Nesterov's avatar Oleg Nesterov Committed by Linus Torvalds
Browse files

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: default avatarOleg 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: default avatarAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
parent 65450ceb

include/linux/pid.h

+4 −2
Original line number Diff line number Diff line
@@ -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,

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);

kernel/pid.c

+16 −5
Original line number Diff line number Diff line
@@ -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)

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