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From: Andy Lutomirski <luto@kernel.org>
To: j@bitron.ch
Cc: Aleksa Sarai <cyphar@cyphar.com>,
	Al Viro <viro@zeniv.linux.org.uk>,
	Jeff Layton <jlayton@kernel.org>,
	"J. Bruce Fields" <bfields@fieldses.org>,
	Arnd Bergmann <arnd@arndb.de>,
	David Howells <dhowells@redhat.com>,
	"Eric W. Biederman" <ebiederm@xmission.com>,
	Christian Brauner <christian@brauner.io>,
	Linux API <linux-api@vger.kernel.org>,
	Andrew Lutomirski <luto@kernel.org>, Jann Horn <jannh@google.com>,
	David Drysdale <drysdale@google.com>,
	Aleksa Sarai <asarai@suse.de>,
	Linux Containers <containers@lists.linux-foundation.org>,
	Linux FS Devel <linux-fsdevel@vger.kernel.org>,
	LKML <linux-kernel@vger.kernel.org>,
	linux-arch <linux-arch@vger.kernel.org>
Subject: Re: [PATCH v4 2/4] namei: O_BENEATH-style path resolution flags
Date: Fri, 23 Nov 2018 08:07:03 -0800
Message-ID: <CALCETrURCXjNMBR6DjujVc6HHHS=CbET81kHS+odur+Bm-z7Tg@mail.gmail.com> (raw)
In-Reply-To: <1ce83cdf6e3168350b69f98f08aaa202bbaa682d.camel@bitron.ch>

> On Nov 23, 2018, at 5:10 AM, Jürg Billeter <j@bitron.ch> wrote:
>
> Hi Aleksa,
>
>> On Tue, 2018-11-13 at 01:26 +1100, Aleksa Sarai wrote:
>> * O_BENEATH: Disallow "escapes" from the starting point of the
>>  filesystem tree during resolution (you must stay "beneath" the
>>  starting point at all times). Currently this is done by disallowing
>>  ".." and absolute paths (either in the given path or found during
>>  symlink resolution) entirely, as well as all "magic link" jumping.
>
> With open_tree(2) and OPEN_TREE_CLONE, will O_BENEATH still be
> necessary?

This discussion reminds me of something I’m uncomfortable with in the
current patches: currently, most of the O_ flags determine some
property of the returned opened file.  The new O_ flags you're adding
don't -- instead, they affect the lookup of the file.  So O_BENEATH
doesn't return a descriptor that can only be used to loop up files
beneath it -- it just controls whether open(2) succeeds or fails.  It
might be nice for the naming of the flags to reflect this.  I also
don't love that we have some magic AT_ flags that work with some
syscalls and some magic O_ flags that work with others.

In this regard, I liked the AT_ naming better.  Although I don't love
adding AT_ flags because the restrict our ability to usefully use the
high bits of the fd in the future.

--Andy

  reply index

Thread overview: 10+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2018-11-12 14:26 [PATCH v4 0/4] namei: O_* flags to restrict path resolution Aleksa Sarai
2018-11-12 14:26 ` [PATCH v4 1/4] namei: split out nd->dfd handling to dirfd_path_init Aleksa Sarai
2018-11-12 14:26 ` [PATCH v4 2/4] namei: O_BENEATH-style path resolution flags Aleksa Sarai
2018-11-23 12:10   ` Jürg Billeter
2018-11-23 16:07     ` Andy Lutomirski [this message]
2018-11-23 16:48       ` Aleksa Sarai
2018-11-23 16:52         ` Aleksa Sarai
2018-11-23 16:58     ` Aleksa Sarai
2018-11-12 14:26 ` [PATCH v4 3/4] namei: O_THISROOT: chroot-like path resolution Aleksa Sarai
2018-11-12 14:26 ` [PATCH v4 4/4] namei: aggressively check for nd->root escape on ".." resolution Aleksa Sarai

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