linux-kernel - Re: [PATCH] sysctl: control functionality of /proc/pid/mem

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Date:	Sat, 21 Jan 2012 10:03:42 +0100
From:	Ingo Molnar <mingo@...e.hu>
To:	Kees Cook <keescook@...omium.org>
Cc:	linux-kernel@...r.kernel.org,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Randy Dunlap <rdunlap@...otime.net>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Borislav Petkov <bp@...en8.de>,
	Vasiliy Kulikov <segoon@...nwall.com>,
	Dan Ballard <dan@...dstab.net>, Jiri Kosina <jkosina@...e.cz>,
	Al Viro <viro@...iv.linux.org.uk>,
	Stephen Wilson <wilsons@...rt.ca>,
	David Rientjes <rientjes@...gle.com>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Eric Paris <eparis@...hat.com>,
	"Serge E. Hallyn" <serge.hallyn@...onical.com>,
	linux-doc@...r.kernel.org
Subject: Re: [PATCH] sysctl: control functionality of /proc/pid/mem


* Kees Cook <keescook@...omium.org> wrote:

> @@ -702,6 +704,9 @@ static int mem_open(struct inode* inode, struct file* file)
>  	struct task_struct *task = get_proc_task(file->f_path.dentry->d_inode);
>  	struct mm_struct *mm;
>  
> +	if (sysctl_proc_pid_mem < 1)
> +		return -EACCES;

This looks like an unprivileged user-space triggerable memory 
leak DoS. The task reference is already acquired at that point.

See how easy it is to introduce bugs with potential security 
side-effects, even when the intention is to increase security?
:-)

( Btw., this is why i generally prefer 'invariant' local
  variable definition blocks that have no serious side effects -
  it makes the flow more obvious. Local variables slip off the 
  eye rather often and don't register as 'real' code.)

Thanks,

	Ingo
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