From c1b2cc1a765aff4df7b22abe6b66014236f73eba Mon Sep 17 00:00:00 2001
From: Miklos Szeredi <mszeredi@redhat.com>
Date: Fri, 29 Jul 2016 12:05:22 +0200
Subject: ovl: check mounter creds on underlying lookup

The hash salting changes meant that we can no longer reuse the hash in the
overlay dentry to look up the underlying dentry.

Instead of lookup_hash(), use lookup_one_len_unlocked() and swith to
mounter's creds (like we do for all other operations later in the series).

Now the lookup_hash() export introduced in 4.6 by 3c9fe8cdff1b ("vfs: add
lookup_hash() helper") is unused and can possibly be removed; its
usefulness negated by the hash salting and the idea that mounter's creds
should be used on operations on underlying filesystems.

Signed-off-by: Miklos Szeredi <mszeredi@redhat.com>
Fixes: 8387ff2577eb ("vfs: make the string hashes salt the hash")

diff --git a/fs/overlayfs/super.c b/fs/overlayfs/super.c
index 5e254b3..cbfa039 100644
--- a/fs/overlayfs/super.c
+++ b/fs/overlayfs/super.c
@@ -423,12 +423,16 @@ static bool ovl_dentry_weird(struct dentry *dentry)
 				  DCACHE_OP_COMPARE);
 }
 
-static inline struct dentry *ovl_lookup_real(struct dentry *dir,
+static inline struct dentry *ovl_lookup_real(struct super_block *ovl_sb,
+					     struct dentry *dir,
 					     struct qstr *name)
 {
+	const struct cred *old_cred;
 	struct dentry *dentry;
 
-	dentry = lookup_hash(name, dir);
+	old_cred = ovl_override_creds(ovl_sb);
+	dentry = lookup_one_len_unlocked(name->name, dir, name->len);
+	revert_creds(old_cred);
 
 	if (IS_ERR(dentry)) {
 		if (PTR_ERR(dentry) == -ENOENT)
@@ -481,7 +485,7 @@ struct dentry *ovl_lookup(struct inode *dir, struct dentry *dentry,
 
 	upperdir = ovl_upperdentry_dereference(poe);
 	if (upperdir) {
-		this = ovl_lookup_real(upperdir, &dentry->d_name);
+		this = ovl_lookup_real(dentry->d_sb, upperdir, &dentry->d_name);
 		err = PTR_ERR(this);
 		if (IS_ERR(this))
 			goto out;
@@ -514,7 +518,8 @@ struct dentry *ovl_lookup(struct inode *dir, struct dentry *dentry,
 		bool opaque = false;
 		struct path lowerpath = poe->lowerstack[i];
 
-		this = ovl_lookup_real(lowerpath.dentry, &dentry->d_name);
+		this = ovl_lookup_real(dentry->d_sb,
+				       lowerpath.dentry, &dentry->d_name);
 		err = PTR_ERR(this);
 		if (IS_ERR(this)) {
 			/*
-- 
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