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* [PATCH AUTOSEL 5.4 29/35] Fix use after free in get_tree_bdev()
       [not found] <>
@ 2020-05-07 14:28 ` Sasha Levin
  0 siblings, 0 replies; only message in thread
From: Sasha Levin @ 2020-05-07 14:28 UTC (permalink / raw)
  To: linux-kernel, stable
  Cc: David Howells, Lukas Czerner, Ian Kent, Al Viro, Linus Torvalds,
	Sasha Levin, linux-fsdevel

From: David Howells <>

[ Upstream commit dd7bc8158b413e0b580c491e8bd18cb91057c7c2 ]

Commit 6fcf0c72e4b9, 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: 6fcf0c72e4b9 ("vfs: add missing blkdev_put() in get_tree_bdev()")
Reported-by: Lukas Czerner <>
Signed-off-by: David Howells <>
cc: Ian Kent <>
cc: Al Viro <>
Signed-off-by: Linus Torvalds <>
Signed-off-by: Sasha Levin <>
 fs/super.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/fs/super.c b/fs/super.c
index cd352530eca90..a288cd60d2aed 100644
--- a/fs/super.c
+++ b/fs/super.c
@@ -1302,8 +1302,8 @@ int get_tree_bdev(struct fs_context *fc,
 	if (bdev->bd_fsfreeze_count > 0) {
-		blkdev_put(bdev, mode);
 		warnf(fc, "%pg: Can't mount, blockdev is frozen", bdev);
+		blkdev_put(bdev, mode);
 		return -EBUSY;

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