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[PATCH] introduce get_task_pid() to fix unsafe get_pid()

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proc_pid_make_inode:

	ei->pid = get_pid(task_pid(task));

I think this is not safe.  get_pid() can be preempted after checking "pid
!= NULL".  Then the task exits, does detach_pid(), and RCU frees the pid.

Signed-off-by: Oleg Nesterov <oleg@tv-sign.ru>
Cc: "Eric W. Biederman" <ebiederm@xmission.com>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>
This commit is contained in:
Oleg Nesterov 2006-10-02 02:18:59 -07:00 committed by Linus Torvalds
parent 1c0d04c9e4
commit 1a657f78dc
3 changed files with 13 additions and 2 deletions
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4
fs/proc/base.c
View file

@ -958,7 +958,7 @@ static struct inode *proc_pid_make_inode(struct super_block * sb, struct task_st
/*
* grab the reference to task.
*/
ei->pid = get_pid(task_pid(task));
ei->pid = get_task_pid(task, PIDTYPE_PID);
if (!ei->pid)
goto out_unlock;
@ -1677,7 +1677,7 @@ static struct dentry *proc_base_instantiate(struct inode *dir,
/*
* grab the reference to the task.
*/
ei->pid = get_pid(task_pid(task));
ei->pid = get_task_pid(task, PIDTYPE_PID);
if (!ei->pid)
goto out_iput;

2
include/linux/pid.h
View file

@ -68,6 +68,8 @@ extern struct task_struct *FASTCALL(pid_task(struct pid *pid, enum pid_type));
extern struct task_struct *FASTCALL(get_pid_task(struct pid *pid,
enum pid_type));
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.

9
kernel/pid.c
View file

@ -304,6 +304,15 @@ struct task_struct *find_task_by_pid_type(int type, int nr)
EXPORT_SYMBOL(find_task_by_pid_type);
struct pid *get_task_pid(struct task_struct *task, enum pid_type type)
{
struct pid *pid;
rcu_read_lock();
pid = get_pid(task->pids[type].pid);
rcu_read_unlock();
return pid;
}
struct task_struct *fastcall get_pid_task(struct pid *pid, enum pid_type type)
{
struct task_struct *result;