linux-kernel - Re: [PATCH v1 2/9] fs/fuse: add FUSE_OWNER_UID_GID

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Message-ID: <CAEivzxd1NtpY_GNnN2=bzwoejn7uUK6Quj_f0_LnnJTBxkE8zQ@mail.gmail.com>
Date: Thu, 29 Aug 2024 19:40:48 +0200
From: Aleksandr Mikhalitsyn <aleksandr.mikhalitsyn@...onical.com>
To: Miklos Szeredi <miklos@...redi.hu>
Cc: Christian Brauner <brauner@...nel.org>, mszeredi@...hat.com, stgraber@...raber.org, 
	linux-fsdevel@...r.kernel.org, Seth Forshee <sforshee@...nel.org>, 
	Amir Goldstein <amir73il@...il.com>, Bernd Schubert <bschubert@....com>, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v1 2/9] fs/fuse: add FUSE_OWNER_UID_GID_EXT extension

On Thu, Aug 29, 2024 at 5:05 PM Miklos Szeredi <miklos@...redi.hu> wrote:
>
> On Thu, 29 Aug 2024 at 16:39, Aleksandr Mikhalitsyn
> <aleksandr.mikhalitsyn@...onical.com> wrote:
>
> > So, your point is to set uid/gid to -1 for FUSE_{READ,WRITE,LOOKUP,RELEASE,...}?
>
> Yes.  Not sure what will happen with those servers that check
> permissions based on these values, but my guess is it's still better
> than sending the unmapped value.

That's an interesting and a bit unexpected proposal. I have not
considered that option before,
because it feels like a bit of a radical change in the fuse protocol semantic,
while I was trying to be extremely careful and not make a revolution
in stable fuse protocol and code ;-)

We even have old commit:
c9582eb0ff7 ("fuse: Fail all requests with invalid uids or gids")
https://github.com/torvalds/linux/commit/c9582eb0ff7d2b560be60eafab29183882cdc82b

At the same time, if *you* propose that, I can't find a single word
against that. :)

You idea also solves problem with ->rename operation:
https://lore.kernel.org/all/20240815092429.103356-10-aleksandr.mikhalitsyn@canonical.com/

because if we just reuse existing fuse header fields and remap values
in them then we don't need
any extension for FUSE_RENAME2.

Let's think about it a bit more and if you confirm that we want to go
this way, then I'll rework my patches.

Kind regards,
Alex

>
> Thanks,
> Miklos