Commit dd7bc815 authored Apr 28, 2020 by David Howells Committed by Linus Torvalds Apr 28, 2020

Fix use after free in get_tree_bdev()



Commit 6fcf0c72, a fix to get_tree_bdev() put a missing blkdev_put() in
the wrong place, before a warnf() that displays the bdev under
consideration rather after it.

This results in a silent lockup in printk("%pg") called via warnf() from
get_tree_bdev() under some circumstances when there's a race with the
blockdev being frozen.  This can be caused by xfstests/tests/generic/085 in
combination with Lukas Czerner's ext4 mount API conversion patchset.  It
looks like it ought to occur with other users of get_tree_bdev() such as
XFS, but apparently doesn't.

Fix this by switching the order of the lines.

Fixes: 6fcf0c72 ("vfs: add missing blkdev_put() in get_tree_bdev()")
Reported-by: Lukas Czerner <lczerner@redhat.com>
Signed-off-by: David Howells <dhowells@redhat.com>
cc: Ian Kent <raven@themaw.net>
cc: Al Viro <viro@zeniv.linux.org.uk>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

parent edb98d16

fs/super.c

+1 −1

Original line number	Diff line number	Diff line
		@@ -1302,8 +1302,8 @@ int get_tree_bdev(struct fs_context *fc,
		mutex_lock(&bdev->bd_fsfreeze_mutex);
		if (bdev->bd_fsfreeze_count > 0) {
		mutex_unlock(&bdev->bd_fsfreeze_mutex);
		blkdev_put(bdev, mode);
		warnf(fc, "%pg: Can't mount, blockdev is frozen", bdev);
		blkdev_put(bdev, mode);
		return -EBUSY;
		}

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