From cd09665ab60b6dcfd416999202f0e9f5e6157797 Mon Sep 17 00:00:00 2001 From: Miklos Szeredi Date: Wed, 31 Oct 2018 12:15:23 +0100 Subject: [PATCH] ovl: check whiteout in ovl_create_over_whiteout() commit 5e1275808630ea3b2c97c776f40e475017535f72 upstream. 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 Signed-off-by: Miklos Szeredi Fixes: e9be9d5e76e3 ("overlay filesystem") Cc: # v3.18 Signed-off-by: Greg Kroah-Hartman --- fs/overlayfs/dir.c | 4 ++++ 1 file changed, 4 insertions(+) diff --git a/fs/overlayfs/dir.c b/fs/overlayfs/dir.c index 0568898393f2..ef11fa7b869e 100644 --- a/fs/overlayfs/dir.c +++ b/fs/overlayfs/dir.c @@ -392,6 +392,10 @@ static int ovl_create_over_whiteout(struct dentry *dentry, struct inode *inode, if (IS_ERR(upper)) goto out_dput; + err = -ESTALE; + if (d_is_negative(upper) || !IS_WHITEOUT(d_inode(upper))) + goto out_dput2; + err = ovl_create_real(wdir, newdentry, cattr, hardlink, true); if (err) goto out_dput2;