[PATCH 5.15.y] mtd: mtdsuper: Fix MTD device reference leak in mtd_get_sb()

[Sasha Levin <sashal@kernel.org>]

From: Wentao Liang <vulab@iscas.ac.cn>

[ Upstream commit 62ee3da38f41bef83c1cf250f6816a0ee187674b ]

mtd_get_sb() is called with a reference to the MTD device already
taken by the caller.  When sget_dev() fails, the function returns the
error without dropping that reference, so the device is never released
and its refcount never reaches zero.  Every mount attempt on an MTD
device whose superblock cannot be set up leaks a reference.

Restore the put_mtd_device() that the fs_context conversion dropped on
this path.

Fixes: 0f071004109d ("mtd: Provide fs_context-aware mount_mtd() replacement")
Cc: stable@vger.kernel.org
Signed-off-by: Wentao Liang <vulab@iscas.ac.cn>
Signed-off-by: Miquel Raynal <miquel.raynal@bootlin.com>
[ sashal: adjusted context around the existing sget_fc() call instead of sget_dev() ]
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
 drivers/mtd/mtdsuper.c | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/drivers/mtd/mtdsuper.c b/drivers/mtd/mtdsuper.c
index 38b6aa849c638..24d6e3540f345 100644
--- a/drivers/mtd/mtdsuper.c
+++ b/drivers/mtd/mtdsuper.c
@@ -63,8 +63,10 @@ static int mtd_get_sb(struct fs_context *fc,
 
 	fc->sget_key = mtd;
 	sb = sget_fc(fc, mtd_test_super, mtd_set_super);
-	if (IS_ERR(sb))
+	if (IS_ERR(sb)) {
+		put_mtd_device(mtd);
 		return PTR_ERR(sb);
+	}
 
 	if (sb->s_root) {
 		/* new mountpoint for an already mounted superblock */
-- 
2.53.0