Re: [PATCH 1/2] break out page allocation warning code

[john stultz <johnstul@us.ibm.com>]

On Thu, 2011-04-21 at 10:29 +0900, KOSAKI Motohiro wrote:
> And one correction.
> ------------------------------------------------------------------
> static ssize_t comm_write(struct file *file, const char __user *buf,
>                                 size_t count, loff_t *offset)
> {
>         struct inode *inode = file->f_path.dentry->d_inode;
>         struct task_struct *p;
>         char buffer[TASK_COMM_LEN];
> 
>         memset(buffer, 0, sizeof(buffer));
>         if (count > sizeof(buffer) - 1)
>                 count = sizeof(buffer) - 1;
>         if (copy_from_user(buffer, buf, count))
>                 return -EFAULT;
> 
>         p = get_proc_task(inode);
>         if (!p)
>                 return -ESRCH;
> 
>         if (same_thread_group(current, p))
>                 set_task_comm(p, buffer);
>         else
>                 count = -EINVAL;
> ------------------------------------------------------------------
> 
> This code doesn't have proper credential check. IOW, you forgot to
> pthread_setuid_np() case.

Sorry, could you expand on this a bit? Google isn't coming up with much
for pthread_setuid_np. Can a thread actually end up with different uid
then the process it is a member of?

Or is same_thread_group not really what I think it is? What would be a
better way to check that the two threads are members of the same
process?

thanks
-john