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

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Date:	Tue, 26 Apr 2011 14:25:15 -0700
From:	john stultz <johnstul@...ibm.com>
To:	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>
Cc:	David Rientjes <rientjes@...gle.com>,
	Dave Hansen <dave@...ux.vnet.ibm.com>, linux-mm@...ck.org,
	linux-kernel@...r.kernel.org, Johannes Weiner <hannes@...xchg.org>,
	Michal Nazarewicz <mina86@...a86.com>,
	Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [PATCH 1/2] break out page allocation warning code

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


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