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

[Wentao Liang]

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 at vger.kernel.org
Signed-off-by: Wentao Liang <vulab at iscas.ac.cn>
---
 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 b7e3763c47f0..22ddeaa7d522 100644
--- a/drivers/mtd/mtdsuper.c
+++ b/drivers/mtd/mtdsuper.c
@@ -31,8 +31,10 @@ static int mtd_get_sb(struct fs_context *fc,
 	int ret;
 
 	sb = sget_dev(fc, MKDEV(MTD_BLOCK_MAJOR, mtd->index));
-	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 */
-- 
2.34.1