All of lore.kernel.org
 help / color / mirror / Atom feed
From: Dongli Zhang <dongli.zhang@oracle.com>
To: axboe@kernel.dk, linux-block@vger.kernel.org
Cc: linux-kernel@vger.kernel.org, jack@suse.cz,
	penguin-kernel@i-love.sakura.ne.jp
Subject: [PATCH 1/1] loop: access lo_backing_file only when the loop device is Lo_bound
Date: Mon, 18 Mar 2019 20:23:17 +0800	[thread overview]
Message-ID: <1552911797-20455-1-git-send-email-dongli.zhang@oracle.com> (raw)

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.

Fixes: 7ccd0791d985 ("loop: Push loop_ctl_mutex down into loop_clr_fd()")
Reported-by: syzbot+9bdc1adc1c55e7fe765b@syzkaller.appspotmail.com
Signed-off-by: Dongli Zhang <dongli.zhang@oracle.com>
Reviewed-by: Jan Kara <jack@suse.cz>
---
 drivers/block/loop.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/block/loop.c b/drivers/block/loop.c
index 1e6edd5..bf1c61c 100644
--- a/drivers/block/loop.c
+++ b/drivers/block/loop.c
@@ -656,7 +656,7 @@ static int loop_validate_file(struct file *file, struct block_device *bdev)
 			return -EBADF;
 
 		l = f->f_mapping->host->i_bdev->bd_disk->private_data;
-		if (l->lo_state == Lo_unbound) {
+		if (l->lo_state != Lo_bound) {
 			return -EINVAL;
 		}
 		f = l->lo_backing_file;
-- 
2.7.4


             reply	other threads:[~2019-03-18 12:19 UTC|newest]

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

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:
  https://en.wikipedia.org/wiki/Posting_style#Interleaved_style

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

  git send-email \
    --in-reply-to=1552911797-20455-1-git-send-email-dongli.zhang@oracle.com \
    --to=dongli.zhang@oracle.com \
    --cc=axboe@kernel.dk \
    --cc=jack@suse.cz \
    --cc=linux-block@vger.kernel.org \
    --cc=linux-kernel@vger.kernel.org \
    --cc=penguin-kernel@i-love.sakura.ne.jp \
    /path/to/YOUR_REPLY

  https://kernel.org/pub/software/scm/git/docs/git-send-email.html

* 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.