From: Al Viro <viro@zeniv.linux.org.uk>
To: Miklos Szeredi <miklos@szeredi.hu>
Cc: Amir Goldstein <amir73il@gmail.com>,
Christian Brauner <brauner@kernel.org>,
Paul Moore <paul@paul-moore.com>,
James Morris <jmorris@namei.org>,
"Serge E . Hallyn" <serge@hallyn.com>,
Mimi Zohar <zohar@linux.ibm.com>,
linux-security-module@vger.kernel.org,
linux-integrity@vger.kernel.org, linux-unionfs@vger.kernel.org,
linux-fsdevel@vger.kernel.org
Subject: Re: [PATCH v3 3/3] fs: store real path instead of fake path in backing file f_path
Date: Wed, 11 Oct 2023 02:37:56 +0100 [thread overview]
Message-ID: <20231011013756.GT800259@ZenIV> (raw)
In-Reply-To: <CAJfpegtbOG0DqyuQ=xt2KDh5WDaZBb0tLJuhqa2jyQfHSMfO-w@mail.gmail.com>
On Tue, Oct 10, 2023 at 08:14:15PM +0200, Miklos Szeredi wrote:
> On Tue, 10 Oct 2023 at 19:41, Al Viro <viro@zeniv.linux.org.uk> wrote:
> >
> > On Tue, Oct 10, 2023 at 05:55:04PM +0100, Al Viro wrote:
> > > On Tue, Oct 10, 2023 at 03:34:45PM +0200, Miklos Szeredi wrote:
> > > > On Tue, 10 Oct 2023 at 15:17, Amir Goldstein <amir73il@gmail.com> wrote:
> > > >
> > > > > Sorry, you asked about ovl mount.
> > > > > To me it makes sense that if users observe ovl paths in writable mapped
> > > > > memory, that ovl should not be remounted RO.
> > > > > Anyway, I don't see a good reason to allow remount RO for ovl in that case.
> > > > > Is there?
> > > >
> > > > Agreed.
> > > >
> > > > But is preventing remount RO important enough to warrant special
> > > > casing of backing file in generic code? I'm not convinced either
> > > > way...
> > >
> > > You definitely want to guarantee that remounting filesystem r/o
> > > prevents the changes of visible contents; it's not just POSIX,
> > > it's a fairly basic common assumption about any local filesystems.
> >
> > Incidentally, could we simply keep a reference to original struct file
> > instead of messing with path?
> >
> > The only caller of backing_file_open() gets &file->f_path as user_path; how
> > about passing file instead, and having backing_file_open() do get_file()
> > on it and stash the sucker into your object?
> >
> > And have put_file_access() do
> > if (unlikely(file->f_mode & FMODE_BACKING))
> > fput(backing_file(file)->file);
> > in the end.
>
> That's much nicer, I like it.
Won't work, unfortunately ;-/ We have the damn thing created on open();
it really can't pin the original file, or we'll never get to closing it.
I don't think this approach could be salvaged - we could make that
reference non-counting outside of mmap(), but we have no good way to
catch the moment when it should be dropped; not without intercepting
vm_ops->close() (and thus vm_ops->open() as well)...
Oh, well..
next prev parent reply other threads:[~2023-10-11 1:38 UTC|newest]
Thread overview: 18+ messages / expand[flat|nested] mbox.gz Atom feed top
2023-10-09 15:37 [PATCH v3 0/3] Reduce impact of overlayfs backing files fake path Amir Goldstein
2023-10-09 15:37 ` [PATCH v3 1/3] fs: get mnt_writers count for an open backing file's real path Amir Goldstein
2023-10-09 15:37 ` [PATCH v3 2/3] fs: create helper file_user_path() for user displayed mapped file path Amir Goldstein
2023-10-09 15:37 ` [PATCH v3 3/3] fs: store real path instead of fake path in backing file f_path Amir Goldstein
2023-10-10 11:59 ` Miklos Szeredi
2023-10-10 13:10 ` Amir Goldstein
2023-10-10 13:17 ` Amir Goldstein
2023-10-10 13:34 ` Miklos Szeredi
2023-10-10 15:22 ` Amir Goldstein
2023-10-10 16:55 ` Al Viro
2023-10-10 17:41 ` Al Viro
2023-10-10 17:57 ` Amir Goldstein
2023-10-10 18:21 ` Al Viro
2023-10-10 18:28 ` Amir Goldstein
2023-10-11 1:26 ` Al Viro
2023-10-10 18:14 ` Miklos Szeredi
2023-10-11 1:37 ` Al Viro [this message]
2023-10-10 11:52 ` [PATCH v3 0/3] Reduce impact of overlayfs backing files fake path Christian Brauner
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=20231011013756.GT800259@ZenIV \
--to=viro@zeniv.linux.org.uk \
--cc=amir73il@gmail.com \
--cc=brauner@kernel.org \
--cc=jmorris@namei.org \
--cc=linux-fsdevel@vger.kernel.org \
--cc=linux-integrity@vger.kernel.org \
--cc=linux-security-module@vger.kernel.org \
--cc=linux-unionfs@vger.kernel.org \
--cc=miklos@szeredi.hu \
--cc=paul@paul-moore.com \
--cc=serge@hallyn.com \
--cc=zohar@linux.ibm.com \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for read-only IMAP folder(s) and NNTP newsgroup(s).