Re: [PATCH] efi: READ_ONCE rng seed size before munmap

[Greg KH]

On Mon, Feb 17, 2020 at 05:09:00PM +0100, Ard Biesheuvel wrote:
> On Mon, 17 Feb 2020 at 16:54, Greg KH <greg@xxxxxxxxx> wrote:
> >
> > On Mon, Feb 17, 2020 at 04:23:03PM +0100, Ard Biesheuvel wrote:
> > > On Mon, 17 Feb 2020 at 13:34, Jason A. Donenfeld <Jason@xxxxxxxxx> wrote:
> > > >
> > > > This function is consistent with using size instead of seed->size
> > > > (except for one place that this patch fixes), but it reads seed->size
> > > > without using READ_ONCE, which means the compiler might still do
> > > > something unwanted. So, this commit simply adds the READ_ONCE
> > > > wrapper.
> > > >
> > > > Signed-off-by: Jason A. Donenfeld <Jason@xxxxxxxxx>
> > > > Cc: Ard Biesheuvel <ardb@xxxxxxxxxx>
> > > > Cc: stable@xxxxxxxxxxxxxxx
> > >
> > > Thanks Jason
> > >
> > > I've queued this in efi/urgent with a fixes: tag rather than a cc:
> > > stable, since it only applies clean to v5.4 and later.
> >
> > Why do that?  That just makes it harder for me to know to pick it up for
> > 5.4 and newer.
> >
> > > We'll need a
> > > backport to 4.14 and 4.19 as well, which has a trivial conflict
> > > (s/add_bootloader_randomness/add_device_randomness/) but we'll need to
> > > wait for this patch to hit Linus's tree first.
> >
> > Ok, if you are going to send it on to me for stable, that's fine, but
> > usually you can just wait for the rejection notices for older kernels
> > before having to worry about this.  In other words, you are doing more
> > work than you have to here :)
> >
> 
> So just
> 
> Cc: <stable@xxxxxxxxxxxxxxx>
> 
> without any context is your preferred method?

If you can provide a "Fixes:" tag showing what commit it does fix,
that's even better as that way I _know_ to try to apply it to older
kernels and if it fails, you will get an email saying it failed.  With
just a cc: stable, I do a "best guess" and don't work very hard if older
kernels do not apply as I don't know if it is relevant or not.

thanks,

greg k-h