linux-kernel - Re: [PATCH] loop: prevent bdev freeing while device in use

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Message-ID: <CA+55aFzqYkX27E8R7Bu8pvn3xO+hKrgMEC7ec5gDz4kr1JbVtQ@mail.gmail.com>
Date:	Mon, 1 Apr 2013 08:16:17 -0700
From:	Linus Torvalds <torvalds@...ux-foundation.org>
To:	Anatol Pomozov <anatol.pomozov@...il.com>
Cc:	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	"Theodore Ts'o" <tytso@....edu>, Salman Qazi <sqazi@...gle.com>,
	Al Viro <viro@...iv.linux.org.uk>, yan@...ux.vnet.ibm.com
Subject: Re: [PATCH] loop: prevent bdev freeing while device in use

On Mon, Apr 1, 2013 at 4:58 AM, Anatol Pomozov <anatol.pomozov@...il.com> wrote:
>
> To prevent use-after-free we need to hold device inode in loop_set_fd()
> and put it later in loop_clr_fd().

Is there something that guarantees that there's only one loop_set_fd()
and one paired loop_clr_fd()?

IOW, what protects us from somebody doing loop_clr_fd() on a device
that hasn't been set up yet, or doing multiple loop_set_fd calls?

I suspect the "lo->lo_state" is part of the answer, but it's very much
not obvious, and I'd want this to be explicitly explained.

              Linus
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