linux-kernel - Re: [PATCH] fs: hardlink creation restrictions

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Date:	Sat, 18 Feb 2012 21:56:26 +0100
From:	Marcin Slusarz <marcin.slusarz@...il.com>
To:	Kees Cook <keescook@...omium.org>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	linux-kernel@...r.kernel.org, Randy Dunlap <rdunlap@...otime.net>,
	Alexander Viro <viro@...iv.linux.org.uk>,
	Ingo Molnar <mingo@...e.hu>, linux-doc@...r.kernel.org,
	linux-fsdevel@...r.kernel.org, kernel-hardening@...ts.openwall.com
Subject: Re: [PATCH] fs: hardlink creation restrictions

On Sat, Feb 18, 2012 at 11:38:57AM -0800, Kees Cook wrote:
> @@ -3052,6 +3119,9 @@ SYSCALL_DEFINE5(linkat, int, olddfd, const char __user *, oldname,
>  	error = mnt_want_write(new_path.mnt);
>  	if (error)
>  		goto out_dput;
> +	error = may_linkat(&old_path);
> +	if (error)
> +		goto out_dput;
>  	error = security_path_link(old_path.dentry, &new_path, new_dentry);
>  	if (error)
>  		goto out_drop_write;

You should give up write access after check failure (i.e. goto out_drop_write).

Marcin
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