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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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