block: fix refcounting in BLKBSZSET

3c522ced · Miklos Szeredi <[email protected]> · 2011-02-24 15:45:41 +01:00

Adam Kovari and others reported that disconnecting an USB drive with
an ntfs-3g filesystem would cause "kernel BUG at fs/inode.c:1421!" to
be triggered.

The BUG could be traced back to ioctl(BLKBSZSET), which would
erroneously decrement the refcount on the bdev.  This is because
blkdev_get() expects the refcount to be already incremented and either
returns success or decrements the refcount and returns an error.

The bug was introduced by e525fd89 (block: make blkdev_get/put()
handle exclusive access), which didn't take into account this behavior
of blkdev_get().

This fixes
  https://bugzilla.kernel.org/show_bug.cgi?id=29202
(and likely 29792 too)

Reported-by: Adam Kovari <[email protected]>
Acked-by: Tejun Heo <[email protected]>
Signed-off-by: Miklos Szeredi <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>

Commit: 3c522cedb572bb8d2e4867f358bdaa7d0c53d88c
Parents: dcace5ac

Changes

1 files changed · +5 −3

File	Status	Add	Del	Content
block/ioctl.c	modified	+5	−3	View file

block/ioctl.c

View file

diff --git a/block/ioctl.c b/block/ioctl.c
index 9049d46..1124cd2 100644
--- a/block/ioctl.c
+++ b/block/ioctl.c
@@ -294,9 +294,11 @@ int blkdev_ioctl(struct block_device *bdev, fmode_t mode, unsigned cmd,
 			return -EINVAL;
 		if (get_user(n, (int __user *) arg))
 			return -EFAULT;
-		if (!(mode & FMODE_EXCL) &&
-		    blkdev_get(bdev, mode | FMODE_EXCL, &bdev) < 0)
-			return -EBUSY;
+		if (!(mode & FMODE_EXCL)) {
+			bdgrab(bdev);
+			if (blkdev_get(bdev, mode | FMODE_EXCL, &bdev) < 0)
+				return -EBUSY;
+		}
 		ret = set_blocksize(bdev, n);
 		if (!(mode & FMODE_EXCL))
 			blkdev_put(bdev, mode | FMODE_EXCL);