linux-kernel - Re: [RFC c/r 4/4] c/r: prctl: Extend PR_SET_MM to set up more mm

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Message-ID: <4F230903.5080504@jp.fujitsu.com>
Date:	Fri, 27 Jan 2012 15:28:51 -0500
From:	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>
To:	keescook@...omium.org
CC:	gorcunov@...nvz.org, linux-kernel@...r.kernel.org,
	akpm@...ux-foundation.org, ebiederm@...ssion.com, xemul@...nvz.org,
	mtk.manpages@...il.com, tj@...nel.org, avagin@...nvz.org,
	serge.hallyn@...onical.com, xemul@...allels.com,
	segoon@...nwall.com, kamezawa.hiroyu@...fujitsu.com
Subject: Re: [RFC c/r 4/4] c/r: prctl: Extend PR_SET_MM to set up more mm_struct
 entries

>> +
>> +       case PR_SET_MM_AUXV:
>> +               if (arg4 > sizeof(mm->saved_auxv))
>> +                       goto out;
>> +               up_read(&mm->mmap_sem);
>> +
>> +               error = -EFAULT;
>> +               if (!copy_from_user(mm->saved_auxv, (const void __user *)addr, arg4))
>> +                       error = 0;
>> +
>> +               return error;
> 
> Is the mmap_sem released here because of the copy_from_user()? Is it
> still safe to write to saved_auxv?

Sure. It's unsafe.

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