linux-ext4 - Re: [PATCH v8 10/19] fanotify: introduce FAN_PRE

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <CAOQ4uxhTiR8eHaf4q0_gLC62CWi9KdaQ05GSeqFkKFkXCH++PA@mail.gmail.com>
Date: Thu, 21 Nov 2024 15:18:36 +0100
From: Amir Goldstein <amir73il@...il.com>
To: Jan Kara <jack@...e.cz>
Cc: Josef Bacik <josef@...icpanda.com>, kernel-team@...com, linux-fsdevel@...r.kernel.org, 
	brauner@...nel.org, torvalds@...ux-foundation.org, viro@...iv.linux.org.uk, 
	linux-xfs@...r.kernel.org, linux-btrfs@...r.kernel.org, linux-mm@...ck.org, 
	linux-ext4@...r.kernel.org
Subject: Re: [PATCH v8 10/19] fanotify: introduce FAN_PRE_ACCESS permission event

On Thu, Nov 21, 2024 at 11:44 AM Jan Kara <jack@...e.cz> wrote:
>
> On Fri 15-11-24 10:30:23, Josef Bacik wrote:
> > From: Amir Goldstein <amir73il@...il.com>
> >
> > Similar to FAN_ACCESS_PERM permission event, but it is only allowed with
> > class FAN_CLASS_PRE_CONTENT and only allowed on regular files and dirs.
> >
> > Unlike FAN_ACCESS_PERM, it is safe to write to the file being accessed
> > in the context of the event handler.
> >
> > This pre-content event is meant to be used by hierarchical storage
> > managers that want to fill the content of files on first read access.
> >
> > Signed-off-by: Amir Goldstein <amir73il@...il.com>
>
> Here I was wondering about one thing:
>
> > +     /*
> > +      * Filesystems need to opt-into pre-content evnets (a.k.a HSM)
> > +      * and they are only supported on regular files and directories.
> > +      */
> > +     if (mask & FANOTIFY_PRE_CONTENT_EVENTS) {
> > +             if (!(path->mnt->mnt_sb->s_iflags & SB_I_ALLOW_HSM))
> > +                     return -EINVAL;
> > +             if (!is_dir && !d_is_reg(path->dentry))
> > +                     return -EINVAL;
> > +     }
>
> AFAICS, currently no pre-content events are generated for directories. So
> perhaps we should refuse directories here as well for now? I'd like to

readdir() does emit PRE_ACCESS (without a range) and also always
emitted ACCESS_PERM. my POC is using that PRE_ACCESS to populate
directories on-demand, although the functionality is incomplete without the
"populate on lookup" event.

> avoid the mistake of original fanotify which had some events available on
> directories but they did nothing and then you have to ponder hard whether
> you're going to break userspace if you actually start emitting them...

But in any case, the FAN_ONDIR built-in filter is applicable to PRE_ACCESS.

Thanks,
Amir.