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From: Ed Maste <emaste@freebsd.org>
To: Aleksa Sarai <cyphar@cyphar.com>
Cc: David Drysdale <drysdale@google.com>, linux-kernel@vger.kernel.org
Subject: : [PATCH v2 1/3] namei: implement O_BENEATH-style AT_* flags
Date: Sat, 27 Oct 2018 12:11:52 +0000	[thread overview]
Message-ID: <20181027121152.GA70269@freebsd.org> (raw)
In-Reply-To: <20181027075348.GN32577@ZenIV.linux.org.uk>

> What is the proposed semantic of O_BENEATH with absolute paths -- I
> believe you don't have an openat(2) on FreeBSD (but please feel free to
> correct me)?

openat(2) is necessary for capability mode (since open(2) is not permitted),
but it turns out it was actually added to FreeBSD earlier than that - the
work was done by a student in the 2007 Google Summer of Code.

From the proposed man page change:
| If the specified path is absolute, O_BENEATH
| allows arbitrary prefix that ends up in the starting directory,
| after which all further resolved components must be under it.

For open, and openat(AT_FDCWD), cwd is used as the top / starting directory.

Once the absolute path traverses the "top" directory in namei all
components must remain within.  The proposed patch allows paths that perhaps
enter, exit, and re-enter the hierarchy -- for example, if /a/b is the top
then /c/d/../../a/b/file would be allowed.

(If you're interested in taking a look the proposed change is available at
https://reviews.freebsd.org/D17714 )

In capability mode absolute paths will always be disallowed.

  reply	other threads:[~2018-10-27 12:12 UTC|newest]

Thread overview: 12+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2018-10-09  6:52 [PATCH v2 0/3] namei: implement various lookup restriction " Aleksa Sarai
2018-10-09  6:52 ` Aleksa Sarai
2018-10-09  6:52 ` [PATCH v2 1/3] namei: implement O_BENEATH-style " Aleksa Sarai
2018-10-09 19:25   ` Andy Lutomirski
2018-10-10  7:07     ` Aleksa Sarai
2018-10-10  7:28       ` Aleksa Sarai
2018-10-12  1:12       ` Andy Lutomirski
2018-10-27  1:41   ` Ed Maste
2018-10-27  7:17     ` Aleksa Sarai
2018-10-27  7:53       ` Al Viro
2018-10-27 12:11         ` Ed Maste [this message]
2018-10-27 15:37         ` Aleksa Sarai

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