All of
 help / color / mirror / Atom feed
From: Jens Axboe <>
To: Dongli Zhang <>,
Subject: Re: [PATCH 1/1] loop: access lo_backing_file only when the loop device is Lo_bound
Date: Mon, 18 Mar 2019 08:21:39 -0600	[thread overview]
Message-ID: <> (raw)
In-Reply-To: <>

On 3/18/19 6:23 AM, Dongli Zhang wrote:
> Commit 758a58d0bc67 ("loop: set GENHD_FL_NO_PART_SCAN after
> blkdev_reread_part()") separates "lo->lo_backing_file = NULL" and
> "lo->lo_state = Lo_unbound" into different critical regions protected by
> loop_ctl_mutex.
> However, there is below race that the NULL lo->lo_backing_file would be
> accessed when the backend of a loop is another loop device, e.g., loop0's
> backend is a file, while loop1's backend is loop0.
> loop0's backend is file            loop1's backend is loop0
> __loop_clr_fd()
>   mutex_lock(&loop_ctl_mutex);
>   lo->lo_backing_file = NULL; --> set to NULL
>   mutex_unlock(&loop_ctl_mutex);
>                                    loop_set_fd()
>                                      mutex_lock_killable(&loop_ctl_mutex);
>                                      loop_validate_file()
>                                        f = l->lo_backing_file; --> NULL
>                                          access if loop0 is not Lo_unbound
>   mutex_lock(&loop_ctl_mutex);
>   lo->lo_state = Lo_unbound;
>   mutex_unlock(&loop_ctl_mutex);
> lo->lo_backing_file should be accessed only when the loop device is
> Lo_bound.
> In fact, the problem has been introduced already in commit 7ccd0791d985
> ("loop: Push loop_ctl_mutex down into loop_clr_fd()") after which
> loop_validate_file() could see devices in Lo_rundown state with which it
> did not count. It was harmless at that point but still.

Thanks, applied.

Jens Axboe

      reply	other threads:[~2019-03-18 14:21 UTC|newest]

Thread overview: 2+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-03-18 12:23 [PATCH 1/1] loop: access lo_backing_file only when the loop device is Lo_bound Dongli Zhang
2019-03-18 14:21 ` Jens Axboe [this message]

Reply instructions:

You may reply publicly to this message via plain-text email
using any one of the following methods:

* Save the following mbox file, import it into your mail client,
  and reply-to-all from there: mbox

  Avoid top-posting and favor interleaved quoting:

* Reply using the --to, --cc, and --in-reply-to
  switches of git-send-email(1):

  git send-email \ \ \ \ \ \ \ \

* If your mail client supports setting the In-Reply-To header
  via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line before the message body.
This is an external index of several public inboxes,
see mirroring instructions on how to clone and mirror
all data and code used by this external index.