[PATCH] ext4: fix possible use after free in ext4_quota_enable

[Pan Bian]

The function frees qf_inode via iput but then pass qf_inode to
lockdep_set_quota_inode on the failure path. This may result in a
use-after-free bug. The patch frees df_inode only when it is never used.

Signed-off-by: Pan Bian <bianpan2016@xxxxxxx>
Fixes: daf647d2dd5("ext4: add lockdep annotations for i_data_sem")
---
 fs/ext4/super.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/fs/ext4/super.c b/fs/ext4/super.c
index 53ff6c2..35689eb 100644
--- a/fs/ext4/super.c
+++ b/fs/ext4/super.c
@@ -5690,9 +5690,9 @@ static int ext4_quota_enable(struct super_block *sb, int type, int format_id,
 	qf_inode->i_flags |= S_NOQUOTA;
 	lockdep_set_quota_inode(qf_inode, I_DATA_SEM_QUOTA);
 	err = dquot_enable(qf_inode, type, format_id, flags);
-	iput(qf_inode);
 	if (err)
 		lockdep_set_quota_inode(qf_inode, I_DATA_SEM_NORMAL);
+	iput(qf_inode);
 
 	return err;
 }
-- 
2.7.4