linux-kernel - Re: [RFC][PATCH 0/5] vfs, overlayfs, cachefiles: Combine I_OVL_INUSE and S_KERNEL

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: <CAOQ4uxgyfQULxH_ot5eAH1V7uAi4FVn5V4aKEHyJtWvnw0SODQ@mail.gmail.com>
Date:   Mon, 31 Jan 2022 18:28:34 +0200
From:   Amir Goldstein <amir73il@...il.com>
To:     David Howells <dhowells@...hat.com>
Cc:     overlayfs <linux-unionfs@...r.kernel.org>,
        linux-cachefs@...hat.com, Miklos Szeredi <miklos@...redi.hu>,
        Christoph Hellwig <hch@...radead.org>,
        Jeff Layton <jlayton@...nel.org>,
        Alexander Viro <viro@...iv.linux.org.uk>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        linux-fsdevel <linux-fsdevel@...r.kernel.org>,
        linux-kernel <linux-kernel@...r.kernel.org>
Subject: Re: [RFC][PATCH 0/5] vfs, overlayfs, cachefiles: Combine I_OVL_INUSE
 and S_KERNEL_FILE and split out no-remove

On Mon, Jan 31, 2022 at 5:12 PM David Howells <dhowells@...hat.com> wrote:
>
>
> Hi Amir,
>
> How about this as a set of patches to do what you suggest[1] and hoist the
> handler functions for I_OVL_INUSE into common code and rename the flag to
> I_EXCL_INUSE.  This can then be shared with cachefiles - allowing me to get
> rid of S_KERNEL_FILE.
>

They look like what I had in mind.
Unfortunately, I had forgotten about another use that ovl makes of the flag
(see comment on patch 1/5). I'd made a suggestion on how to get rid of that use
case, but I hope this won't complicate things too much for you.

> I did split out the functionality for preventing file/dir removal to a
> separate flag, I_NO_REMOVE, so that it's not tied to I_EXCL_INUSE in case
> overlayfs doesn't want to use it.  The downside to that, though is that it
> requires a separate locking of i_lock to set/clear it.
>
> I also added four general tracepoints to log successful lock/unlock,
> failure to lock and a bad unlock.  The lock tracepoints log which driver
> asked for the lock and all tracepoints allow the driver to log an arbitrary
> reference number (in cachefiles's case this is the object debug ID).
>
> Questions:
>
>  (1) Should it be using a flag in i_state or a flag in i_flags?  I'm not
>      sure what the difference is really.

Me neither.

>
>  (2) Do we really need to take i_lock when testing I_EXCL_INUSE?  Would
>      READ_ONCE() suffice?
>

For ovl_is_inuse() I think READ_ONCE() should suffice.

Thanks,
Amir.