linux-kernel - Re: [GIT PULL] /dev/random bug fixes for 4.12

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Message-ID: <CA+55aFxGMYWW7ZxTL+1XCMuWPWUse7+FqhLFuW-AR3efGT6cmA@mail.gmail.com>
Date:   Fri, 2 Jun 2017 16:30:39 -0700
From:   Linus Torvalds <torvalds@...ux-foundation.org>
To:     "Theodore Ts'o" <tytso@....edu>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [GIT PULL] /dev/random bug fixes for 4.12

On Fri, Jun 2, 2017 at 2:30 PM, Theodore Ts'o <tytso@....edu> wrote:
>
> Fix a race on architectures with prioritized interrupts (such as m68k)
> which can causes crashes in drivers/char/random.c:get_reg().

I don't think this has anything to do with prioritized interrupts,
just possibility of nesting (which can happen anywhere).

I've pulled this, but I really am not all that happy about it. It adds
a interrupt disable/enable in something that might be pretty
timing-ciritcal.

And I really don't think it needs it. We don't actually care about the
reg_idx value being reliable, so the code could easily have just done
some READ_ONCE/WRITE_ONCE thing. Something like the attached
(UNTESTED!) patch instead.

But it's in my tree now in your form.

                Linus

View attachment "patch.diff" of type "text/plain" (813 bytes)