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

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Message-ID: <CAGXu5jJQVWS60m5W1-OvDCDixe=kVU2HxPP1C3zNCVgWcXzdDA@mail.gmail.com>
Date:	Sat, 18 Feb 2012 17:36:36 -0800
From:	Kees Cook <keescook@...omium.org>
To:	Marcin Slusarz <marcin.slusarz@...il.com>
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 12:56 PM, Marcin Slusarz
<marcin.slusarz@...il.com> wrote:
> 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).

Ah! Thanks, yes, good catch. I will move the check before mnt_want_write().

-Kees

-- 
Kees Cook
ChromeOS Security
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