Re: [RFC PATCH] f*xattr: allow O_PATH descriptors

From: Amir Goldstein <amir73il@gmail.com>
To: Andreas Dilger <adilger@dilger.ca>
Cc: "Christian Göttsche" <cgzones@googlemail.com>,
	selinux@vger.kernel.org, "Miklos Szeredi" <mszeredi@redhat.com>,
	"Linux API" <linux-api@vger.kernel.org>,
	linux-man <linux-man@vger.kernel.org>,
	"Alexander Viro" <viro@zeniv.linux.org.uk>,
	linux-fsdevel <linux-fsdevel@vger.kernel.org>,
	linux-kernel <linux-kernel@vger.kernel.org>
Subject: Re: [RFC PATCH] f*xattr: allow O_PATH descriptors
Date: Thu, 9 Jun 2022 07:35:56 +0300	[thread overview]
Message-ID: <CAOQ4uxh1QG_xJ0Ffh=wKksxWKm1ioazmc8SxeYYH9yHT1PMasg@mail.gmail.com> (raw)
In-Reply-To: <08A11E25-0208-4B4F-8759-75C1841E7017@dilger.ca>

On Wed, Jun 8, 2022 at 9:01 PM Andreas Dilger <adilger@dilger.ca> wrote:
>
> On Jun 7, 2022, at 9:31 AM, Christian Göttsche <cgzones@googlemail.com> wrote:
> >
> > From: Miklos Szeredi <mszeredi@redhat.com>
> >
> > Support file descriptors obtained via O_PATH for extended attribute
> > operations.
> >
> > Extended attributes are for example used by SELinux for the security
> > context of file objects. To avoid time-of-check-time-of-use issues while
> > setting those contexts it is advisable to pin the file in question and
> > operate on a file descriptor instead of the path name. This can be
> > emulated in userspace via /proc/self/fd/NN [1] but requires a procfs,
> > which might not be mounted e.g. inside of chroots, see[2].
>
> Will this allow get/set xattrs directly on symlinks?  That is one problem
> that we have with some of the xattrs that are inherited on symlinks, but
> there is no way to change them.  Allowing setxattr directly on a symlink
> would be very useful.

It is possible.
See: https://github.com/libfuse/libfuse/pull/514

That's why Miklos withdrew this patch:
https://lore.kernel.org/linux-fsdevel/CAOssrKeV7g0wPg4ozspG4R7a+5qARqWdG+GxWtXB-MCfbVM=9A@mail.gmail.com/

Thanks,
Amir.