[PATCH 4.9 32/44] ext4: check to make sure the rename(2)s destination is not freed

From: Greg Kroah-Hartman
Date: Thu Sep 27 2018 - 05:30:17 EST


4.9-stable review patch. If anyone has any objections, please let me know.

------------------

From: Theodore Ts'o <tytso@xxxxxxx>

commit b50282f3241acee880514212d88b6049fb5039c8 upstream.

If the destination of the rename(2) system call exists, the inode's
link count (i_nlinks) must be non-zero. If it is, the inode can end
up on the orphan list prematurely, leading to all sorts of hilarity,
including a use-after-free.

https://bugzilla.kernel.org/show_bug.cgi?id=200931

Signed-off-by: Theodore Ts'o <tytso@xxxxxxx>
Reported-by: Wen Xu <wen.xu@xxxxxxxxxx>
Cc: stable@xxxxxxxxxxxxxxx
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>

---
fs/ext4/namei.c | 6 ++++++
1 file changed, 6 insertions(+)

--- a/fs/ext4/namei.c
+++ b/fs/ext4/namei.c
@@ -3527,6 +3527,12 @@ static int ext4_rename(struct inode *old
int credits;
u8 old_file_type;

+ if (new.inode && new.inode->i_nlink == 0) {
+ EXT4_ERROR_INODE(new.inode,
+ "target of rename is already freed");
+ return -EFSCORRUPTED;
+ }
+
if ((ext4_test_inode_flag(new_dir, EXT4_INODE_PROJINHERIT)) &&
(!projid_eq(EXT4_I(new_dir)->i_projid,
EXT4_I(old_dentry->d_inode)->i_projid)))