4.9-stable review patch. If anyone has any objections, please let me know.
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From: Miklos Szeredi mszeredi@redhat.com
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 xiakaixu1987@gmail.com Signed-off-by: Miklos Szeredi mszeredi@redhat.com Fixes: e9be9d5e76e3 ("overlay filesystem") Cc: stable@vger.kernel.org # v3.18 Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org
--- 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;