linux-kernel - Re: 18-year-old bug

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Message-ID: <CAO6TR8UGkUGMY7sN6X8az7OnnERC0yARqHHRTq7AZjhEoF+5Ng@mail.gmail.com>
Date:	Wed, 6 Jan 2016 09:24:03 -0700
From:	Jeff Merkey <linux.mdb@...il.com>
To:	Albert Cahalan <acahalan@...il.com>
Cc:	linux-kernel@...r.kernel.org
Subject: Re: 18-year-old bug

On 1/6/16, Albert Cahalan <acahalan@...il.com> wrote:
> This bug was introduced with SE Linux, 18 years ago. People have been
> adding hacks to work around it as the bug bites them, but really the
> bug ought to be fixed. Signals related to a tty are supposed to come
> from the kernel. This got broken for pty devices. We now act as if
> the signal is sent from the process on the master side of the pty.
> That isn't right; the signal is supposed to come from the tty itself
> and thus have a kernel identity.
>
> How to reproduce:
>
> Copy /bin/sleep to /tmp/work and /tmp/fail. Start up xterm, run
> /tmp/work in the window, close the window, and see the process gone.
> Now repeat that for /tmp/fail, but run "su -" in the window first.
> Meanwhile, to view the problem, run this in another window:
>
> ps -Cwork -Cfail -o tty,pid,ppid,tpgid,pgid,sid,ruid,euid,comm
>
> (so like "/tmp/fail 100" or however much time you need)
>
> I first saw the problem when I was maintaining top. People would
> run top as root, close the window, and then find that top got stuck
> spinning on select. Eventually top was hacked up to work around the
> kernel bug, but really we shouldn't have userspace trying to work
> around kernel bugs. I tried to fix it back then, but got a bit lost
> in the then-new code. Sorry. Since then, I've become insanely busy
> with ten kids. I'd really appreciate if somebody could take a shot
> at fixing this bug. It seems to have hit a coworker a few months back,
> and he is just living with it. (ouch)
> --
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Point me to the code in kernel and I'll take stab at it.  There are a
bunch of old bugs lurking around the kernel.

Jeff
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