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From:   "Jason A. Donenfeld" <Jason@zx2c4.com>
Date:   Wed, 16 Nov 2022 19:56:11 +0100
Message-ID: <CAHmME9os4tUqKbz7jdj6goA-SukqTmGEKxi36A97LTtv-QE+bA@mail.gmail.com>
Subject: Re: [PATCH RFC v1 5/6] efi: efivarfs: prohibit reading random seed variables
To:     Ard Biesheuvel <ardb@kernel.org>
Cc:     linux-efi@vger.kernel.org, linux-crypto@vger.kernel.org,
        Lennart Poettering <lennart@poettering.net>
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On Wed, Nov 16, 2022 at 6:05 PM Ard Biesheuvel <ardb@kernel.org> wrote:
>
> On Wed, 16 Nov 2022 at 17:17, Jason A. Donenfeld <Jason@zx2c4.com> wrote:
> >
> > Variables in the random seed GUID must remain secret, so deny all reads
> > to them.
> >
> > Signed-off-by: Jason A. Donenfeld <Jason@zx2c4.com>
> > ---
> >  fs/efivarfs/file.c | 3 +++
> >  1 file changed, 3 insertions(+)
> >
> > diff --git a/fs/efivarfs/file.c b/fs/efivarfs/file.c
> > index d57ee15874f9..08996ba3a373 100644
> > --- a/fs/efivarfs/file.c
> > +++ b/fs/efivarfs/file.c
> > @@ -76,6 +76,9 @@ static ssize_t efivarfs_file_read(struct file *file, char __user *userbuf,
> >         while (!__ratelimit(&file->f_cred->user->ratelimit))
> >                 msleep(50);
> >
> > +       if (guid_equal(&var->var.VendorGuid, &LINUX_EFI_RANDOM_SEED_TABLE_GUID))
> > +               return -EPERM;
> > +
> >         err = efivar_entry_size(var, &datasize);
> >
> >         /*
>
> I'd prefer it if we could just disregard them entirely, i.e., never
> enumerate them so that they don't appear in the file system.

Okay, sure, I can make that happen I think.

And then I suppose that if you try to create anything under that GUID,
it should just fail.

Jason