Re: [PATCH v2 0/2] Use exclusive lock for file_remove_privs

[Christian Brauner <brauner@kernel.org>]

On Tue, Sep 05, 2023 at 08:02:59PM +0200, David Sterba wrote:
> On Thu, Aug 31, 2023 at 01:24:29PM +0200, Bernd Schubert wrote:
> > While adding shared direct IO write locks to fuse Miklos noticed
> > that file_remove_privs() needs an exclusive lock. I then
> > noticed that btrfs actually has the same issue as I had in my patch,
> > it was calling into that function with a shared lock.
> > This series adds a new exported function file_needs_remove_privs(),
> > which used by the follow up btrfs patch and will be used by the
> > DIO code path in fuse as well. If that function returns any mask
> > the shared lock needs to be dropped and replaced by the exclusive
> > variant.
> > 
> > Note: Compilation tested only.
> 
> The fix makes sense, there should be no noticeable performance impact,
> basically the same check is done in the newly exported helper for the
> IS_NOSEC bit.  I can give it a test locally for the default case, I'm
> not sure if we have specific tests for the security layers in fstests.
> 
> Regarding merge, I can take the two patches via btrfs tree or can wait
> until the export is present in Linus' tree in case FUSE needs it
> independently.

Both fuse and btrfs need it afaict. We can grab it and provide a tag
post -rc1? Whatever works best.