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Date:   Wed, 17 Feb 2021 16:32:21 +0000
From:   Chris Down <chris@chrisdown.name>
To:     Petr Mladek <pmladek@suse.com>
Cc:     linux-kernel@vger.kernel.org,
        Sergey Senozhatsky <sergey.senozhatsky@gmail.com>,
        John Ogness <john.ogness@linutronix.de>,
        Johannes Weiner <hannes@cmpxchg.org>,
        Andrew Morton <akpm@linux-foundation.org>,
        Steven Rostedt <rostedt@goodmis.org>,
        Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        Kees Cook <keescook@chromium.org>, kernel-team@fb.com
Subject: Re: code style: Re: [PATCH v4] printk: Userspace format enumeration
 support
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Chris Down writes:
>open(f);
>  debugfs_file_get(f);
>  fops->open();
>    inode->private = ps;
>  debugfs_file_put(f);
>
>remove_printk_fmt_sec(); /* kfree ps */
>
>read(f);
>  debugfs_file_get(f);
>  fops->read();
>    ps = inode->private;  /* invalid */
>  debugfs_file_put(f);

Er, sorry, inode->private is populated at creation time, not at open(). The 
same general concern applies though -- as far as I can tell there's some period 
where we may be able to _read() and `ps` has already been freed.