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

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Message-ID: <CAKv+Gu9v0AffO_A_T11aGwGAgWqEEvai7S0_0Tw1B+OfxOm8ow@mail.gmail.com>
Date:   Mon, 17 Feb 2020 17:40:45 +0100
From:   Ard Biesheuvel <ardb@...nel.org>
To:     Greg KH <greg@...ah.com>
Cc:     "Jason A. Donenfeld" <Jason@...c4.com>,
        linux-efi <linux-efi@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        stable <stable@...r.kernel.org>
Subject: Re: [PATCH] efi: READ_ONCE rng seed size before munmap

On Mon, 17 Feb 2020 at 17:33, Greg KH <greg@...ah.com> wrote:
>
> On Mon, Feb 17, 2020 at 05:09:00PM +0100, Ard Biesheuvel wrote:
> > On Mon, 17 Feb 2020 at 16:54, Greg KH <greg@...ah.com> 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@...c4.com> 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@...c4.com>
> > > > > Cc: Ard Biesheuvel <ardb@...nel.org>
> > > > > Cc: stable@...r.kernel.org
> > > >
> > > > 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@...r.kernel.org>
> >
> > 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.
>

OK, will do.