The patch below does not apply to the 4.4-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@vger.kernel.org.

thanks,

greg k-h

------------------ original commit in Linus's tree ------------------

From 5e1275808630ea3b2c97c776f40e475017535f72 Mon Sep 17 00:00:00 2001

From: Miklos Szeredi mszeredi@redhat.com 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@gmail.com Signed-off-by: Miklos Szeredi mszeredi@redhat.com Fixes: e9be9d5e76e3 ("overlay filesystem") Cc: stable@vger.kernel.org # 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))