linux-kernel - [PATCH] bad bd_fsfreeze_count in freeze

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Message-ID: <20130914023655.GA3212@server.mountain-tech.net>
Date:	Fri, 13 Sep 2013 20:36:55 -0600
From:	Chuck Coffing <clc@...m.mit.edu>
To:	linux-kernel@...r.kernel.org
Cc:	Alexander Viro <viro@...iv.linux.org.uk>
Subject: [PATCH] bad bd_fsfreeze_count in freeze_bdev

Hi,

An error path in freeze_bdev screws up the freeze count.

Consider:
- call freeze_bdev with a bdev that's unmounted (stupidity or a race)
- bd_fsfreeze_count is unconditionally incremented on entry
- can't get the sb; error out
- bd_fsfreeze_count is not decremented (oops!)
- call freeze_bdev again just for obnoxiousness...
- since bd_fsfreeze_count is already nonzero, sb is assumed good and deref'd

(CC me, I'm not subscribed)


diff --git a/fs/block_dev.c b/fs/block_dev.c
index c3549ed..f1c5561 100644
--- a/fs/block_dev.c
+++ b/fs/block_dev.c
@@ -253,6 +253,7 @@ struct super_block *freeze_bdev(struct block_device *bdev)
 	}
 	deactivate_super(sb);
  out:
+	bdev->bd_fsfreeze_count--;
 	sync_blockdev(bdev);
 	mutex_unlock(&bdev->bd_fsfreeze_mutex);
 	return sb;	/* thaw_bdev releases s->s_umount */
--
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