linux-kernel - Re: [PATCH] signal/GenWQE: Fix sending of SIGKILL

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Date:   Thu, 20 Sep 2018 15:12:58 +0200
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     "Eric W. Biederman" <ebiederm@...ssion.com>
Cc:     linux-kernel@...r.kernel.org,
        Frank Haverkamp <haver@...ux.vnet.ibm.com>,
        Joerg-Stephan Vogt <jsvogt@...ibm.com>,
        Michael Jung <mijung@....net>,
        Michael Ruettger <michael@...ra.de>,
        Kleber Sacilotto de Souza <klebers@...ux.vnet.ibm.com>,
        Sebastian Ott <sebott@...ux.vnet.ibm.com>,
        "Eberhard S. Amann" <esa@...ux.vnet.ibm.com>,
        Gabriel Krisman Bertazi <krisman@...ux.vnet.ibm.com>,
        "Guilherme G. Piccoli" <gpiccoli@...ux.vnet.ibm.com>
Subject: Re: [PATCH] signal/GenWQE: Fix sending of SIGKILL

On Thu, Sep 13, 2018 at 12:48:43PM +0200, Eric W. Biederman wrote:
> 
> The genweq_add_file and genwqe_del_file by caching current without
> using reference counting embed the assumption that a file descriptor
> will never be passed from one process to another.  It even embeds the
> assumption that the the thread that opened the file will be in
> existence when the process terminates.   Neither of which are
> guaranteed to be true.
> 
> Therefore replace caching the task_struct of the opener with
> pid of the openers thread group id.  All the knowledge of the
> opener is used for is as the target of SIGKILL and a SIGKILL
> will kill the entire process group.
> 
> Rename genwqe_force_sig to genwqe_terminate, remove it's unncessary
> signal argument, update it's ownly caller, and use kill_pid
> instead of force_sig.
> 
> The work force_sig does in changing signal handling state is not
> relevant to SIGKILL sent as SEND_SIG_PRIV.  The exact same processess
> will be killed just with less work, and less confusion.  The work done
> by force_sig is really only needed for handling syncrhonous
> exceptions.
> 
> It will still be possible to cause genwqe_device_remove to wait 8
> seconds by passing a file descriptor to another process but the possible
> user after free is fixed.
> 
> Fixes: eaf4722d4645 ("GenWQE Character device and DDCB queue")
> Cc: stable@...r.kernel.org
> Cc: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
> Cc: Frank Haverkamp <haver@...ux.vnet.ibm.com>
> Cc: Joerg-Stephan Vogt <jsvogt@...ibm.com>
> Cc: Michael Jung <mijung@....net>
> Cc: Michael Ruettger <michael@...ra.de>
> Cc: Kleber Sacilotto de Souza <klebers@...ux.vnet.ibm.com>
> Cc: Sebastian Ott <sebott@...ux.vnet.ibm.com>
> Cc: Eberhard S. Amann <esa@...ux.vnet.ibm.com>
> Cc: Gabriel Krisman Bertazi <krisman@...ux.vnet.ibm.com>
> Cc: Guilherme G. Piccoli <gpiccoli@...ux.vnet.ibm.com>
> Signed-off-by: "Eric W. Biederman" <ebiederm@...ssion.com>
> ---
> 
> Greg I intend to take this through my signal tree, but if you would
> rather take this through your driver tree please feel free.

No objection from me for you to take it through your tree:

Acked-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>