The patch below does not apply to the 4.9-stable tree.
If someone wants it applied there, or to any other stable or longterm
tree, then please email the backport, including the original git commit
id to <stable@xxxxxxxxxxxxxxx>.
thanks,
greg k-h
------------------ original commit in Linus's tree ------------------
>From 5e1275808630ea3b2c97c776f40e475017535f72 Mon Sep 17 00:00:00 2001
From: Miklos Szeredi <mszeredi@xxxxxxxxxx>
Date: Wed, 31 Oct 2018 12:15:23 +0100
Subject: [PATCH] ovl: check whiteout in ovl_create_over_whiteout()
Kaixuxia repors that it's possible to crash overlayfs by removing the
whiteout on the upper layer before creating a directory over it. This is a
reproducer:
mkdir lower upper work merge
touch lower/file
mount -t overlay overlay -olowerdir=lower,upperdir=upper,workdir=work merge
rm merge/file
ls -al merge/file
rm upper/file
ls -al merge/
mkdir merge/file
Before commencing with a vfs_rename(..., RENAME_EXCHANGE) verify that the
lookup of "upper" is positive and is a whiteout, and return ESTALE
otherwise.
Reported by: kaixuxia <xiakaixu1987@xxxxxxxxx>
Signed-off-by: Miklos Szeredi <mszeredi@xxxxxxxxxx>
Fixes: e9be9d5e76e3 ("overlay filesystem")
Cc: <stable@xxxxxxxxxxxxxxx> # v3.18
diff --git a/fs/overlayfs/dir.c b/fs/overlayfs/dir.c
index ce1857fb5434..c6289147c787 100644
--- a/fs/overlayfs/dir.c
+++ b/fs/overlayfs/dir.c
@@ -462,6 +462,10 @@ static int ovl_create_over_whiteout(struct dentry *dentry, struct inode *inode,
if (IS_ERR(upper))
goto out_unlock;
+ err = -ESTALE;
+ if (d_is_negative(upper) || !IS_WHITEOUT(d_inode(upper)))
+ goto out_dput;
+
newdentry = ovl_create_temp(workdir, cattr);
err = PTR_ERR(newdentry);
if (IS_ERR(newdentry))
