lists.openwall.net   lists  /  announce  owl-users  owl-dev  john-users  john-dev  passwdqc-users  yescrypt  popa3d-users  /  oss-security  kernel-hardening  musl  sabotage  tlsify  passwords  /  crypt-dev  xvendor  /  Bugtraq  Full-Disclosure  linux-kernel  linux-netdev  linux-ext4  linux-hardening  linux-cve-announce  PHC 
Open Source and information security mailing list archives
 
Hash Suite: Windows password security audit tool. GUI, reports in PDF.
[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]
Message-ID: <CAHk-=wjQxHwdC61ore062Hc5PAF2o6CJnDG_NsQe+e599RovJw@mail.gmail.com>
Date:   Sun, 14 Nov 2021 11:02:31 -0800
From:   Linus Torvalds <torvalds@...ux-foundation.org>
To:     Thomas Gleixner <tglx@...utronix.de>
Cc:     Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        "the arch/x86 maintainers" <x86@...nel.org>
Subject: Re: [GIT pull] timers/urgent for v5.16-rc1

On Sun, Nov 14, 2021 at 5:31 AM Thomas Gleixner <tglx@...utronix.de> wrote:
>
> +       /*
> +        * A copied work entry from the old task is not meaningful, clear it.
> +        * N.B. init_task_work will not do this.
> +        */
> +       memset(&p->posix_cputimers_work.work, 0,
> +              sizeof(p->posix_cputimers_work.work));
> +       init_task_work(&p->posix_cputimers_work.work,
> +                      posix_cpu_timers_work);

Ugh.

Instead of the added four lines of comment, and two lines of
"memset()", maybe this should just have made init_task_work() DTRT?

Yes,. I see this:

        /* Protect against double add, see task_tick_numa and task_numa_work */
        p->numa_work.next               = &p->numa_work;
        ...
        init_task_work(&p->numa_work, task_numa_work);

but I think that one is so subtle and such a special case that it
should have been updated - just make that magic special flag happen
after the init_task_work.

A lot of the other cases seem to zero-initialize things elsewhere
(generally with kzalloc()), but I note that at least
io_ring_exit_work() seems to have this:

        struct io_tctx_exit exit;
        ...
        init_task_work(&exit.task_work, io_tctx_exit_cb);

and the ->next pointer is never set to NULL.

Now, in 99% of all cases the ->next pointer simply doesn't matter,
because task_work_add() will only set it, not caring about the old
value.

But apparently it matters for posix_cputimers_work and for numa_work,
and so I think it's very illogical that init_task_work() will not
actually initialize it properly.

Hmm?

I've pulled this, but it really looks like the wrong solution to the
whole "uninitialized data".

And that task_tick_numa() special case is truly horrendous, and really
should go after the init_task_work() regardless, exactly because you'd
expect that init_task_work() to initialize the work even if it doesn't
happen to right now.

Or is somebody doing init_task_work() to only change the work-function
on an already initialized work entry? Becuase that sounds both racy
and broken to me, and none of the things I looked at from a quick grep
looked like that at all.

              Linus

Powered by blists - more mailing lists

Powered by Openwall GNU/*/Linux Powered by OpenVZ