linux-kernel - Re: [RFC PATCH v14 06/10] landlock: Add syscall implementation

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Date:   Tue, 17 Mar 2020 18:51:44 +0100
From:   Mickaël Salaün <mic@...ikod.net>
To:     Al Viro <viro@...iv.linux.org.uk>
Cc:     linux-kernel@...r.kernel.org,
        Andy Lutomirski <luto@...capital.net>,
        Arnd Bergmann <arnd@...db.de>,
        Casey Schaufler <casey@...aufler-ca.com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        James Morris <jmorris@...ei.org>, Jann Horn <jann@...jh.net>,
        Jonathan Corbet <corbet@....net>,
        Kees Cook <keescook@...omium.org>,
        Michael Kerrisk <mtk.manpages@...il.com>,
        Mickaël Salaün <mickael.salaun@....gouv.fr>,
        "Serge E . Hallyn" <serge@...lyn.com>,
        Shuah Khan <shuah@...nel.org>,
        Vincent Dagonneau <vincent.dagonneau@....gouv.fr>,
        kernel-hardening@...ts.openwall.com, linux-api@...r.kernel.org,
        linux-arch@...r.kernel.org, linux-doc@...r.kernel.org,
        linux-fsdevel@...r.kernel.org, linux-kselftest@...r.kernel.org,
        linux-security-module@...r.kernel.org, x86@...nel.org
Subject: Re: [RFC PATCH v14 06/10] landlock: Add syscall implementation


On 17/03/2020 17:47, Al Viro wrote:
> On Mon, Feb 24, 2020 at 05:02:11PM +0100, Mickaël Salaün wrote:
> 
>> +static int get_path_from_fd(u64 fd, struct path *path)
> 
>> +	/*
>> +	 * Only allows O_PATH FD: enable to restrict ambiant (FS) accesses
>> +	 * without requiring to open and risk leaking or misuing a FD.  Accept
>> +	 * removed, but still open directory (S_DEAD).
>> +	 */
>> +	if (!(f.file->f_mode & FMODE_PATH) || !f.file->f_path.mnt ||
> 					      ^^^^^^^^^^^^^^^^^^^
> Could you explain what that one had been be about?  The underlined
> subexpression is always false; was that supposed to check some
> condition and if so, which one?
> 

This was just to be sure that the next assignment "path->mnt =
f.file->f_path.mnt;" always creates a valid path. If this is always
true, I will remove it.