linux-kernel - Re: [RFC 1/2] proc: Return if nothing to unmount

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Date:   Sun, 10 Sep 2017 15:41:52 -0400
From:   Rik van Riel <riel@...riel.com>
To:     Al Viro <viro@...IV.linux.org.uk>,
        Gargi Sharma <gs051095@...il.com>
CC:     linux-kernel@...r.kernel.org, julia.lawall@...6.fr,
        akpm@...ux-foundation.org, mingo@...nel.org,
        pasha.tatashin@...cle.com, ktkhai@...tuozzo.com, oleg@...hat.com,
        wangkefeng.wang@...wei.org
Subject: Re: [RFC 1/2] proc: Return if nothing to unmount



On September 9, 2017 2:31:35 PM EDT, Al Viro <viro@...IV.linux.org.uk> wrote:
>On Sat, Sep 09, 2017 at 06:03:16PM +0530, Gargi Sharma wrote:
>> If a task exits before procfs is mounted, proc_flush_task_mnt will
>> be called with a NULL mnt parameter. In that case, not only is there
>> nothing to unhash, but trying to do so will oops the kernel with a
>> null pointer dereference.
>
>You are misreading that sucker.  It's about userland mounts, it's about
>the internal ones in pidns, for each pidns the process belongs to.
>
>IOW, what you are adding is dead code.  The very first alloc_pid() in
>that pidns should've called pid_ns_prepare_proc(), which creates that
>vfsmount.

Huh, my bad. I wonder why Gargi's code ran into a null pointer dereference on a null mnt pointer, then...
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