1 files changed, 71 insertions, 0 deletions
diff --git a/fs/namei.c b/fs/namei.c
index 45c702edce3c..1067f7a0287a 100644
--- a/fs/namei.c
+++ b/fs/namei.c
@@ -2272,6 +2272,8 @@ EXPORT_SYMBOL(vfs_path_lookup);
  *
  * Note that this routine is purely a helper for filesystem usage and should
  * not be called by generic code.
+ *
+ * The caller must hold base->i_mutex.
  */
 struct dentry *lookup_one_len(const char *name, struct dentry *base, int len)
 {
@@ -2315,6 +2317,75 @@ struct dentry *lookup_one_len(const char *name, struct dentry *base, int len)
 }
 EXPORT_SYMBOL(lookup_one_len);
 
+/**
+ * lookup_one_len_unlocked - filesystem helper to lookup single pathname component
+ * @name:	pathname component to lookup
+ * @base:	base directory to lookup from
+ * @len:	maximum length @len should be interpreted to
+ *
+ * Note that this routine is purely a helper for filesystem usage and should
+ * not be called by generic code.
+ *
+ * Unlike lookup_one_len, it should be called without the parent
+ * i_mutex held, and will take the i_mutex itself if necessary.
+ */
+struct dentry *lookup_one_len_unlocked(const char *name,
+				       struct dentry *base, int len)
+{
+	struct qstr this;
+	unsigned int c;
+	int err;
+	struct dentry *ret;
+
+	this.name = name;
+	this.len = len;
+	this.hash = full_name_hash(name, len);
+	if (!len)
+		return ERR_PTR(-EACCES);
+
+	if (unlikely(name[0] == '.')) {
+		if (len < 2 || (len == 2 && name[1] == '.'))
+			return ERR_PTR(-EACCES);
+	}
+
+	while (len--) {
+		c = *(const unsigned char *)name++;
+		if (c == '/' || c == '\0')
+			return ERR_PTR(-EACCES);
+	}
+	/*
+	 * See if the low-level filesystem might want
+	 * to use its own hash..
+	 */
+	if (base->d_flags & DCACHE_OP_HASH) {
+		int err = base->d_op->d_hash(base, &this);
+		if (err < 0)
+			return ERR_PTR(err);
+	}
+
+	err = inode_permission(base->d_inode, MAY_EXEC);
+	if (err)
+		return ERR_PTR(err);
+
+	/*
+	 * __d_lookup() is used to try to get a quick answer and avoid the
+	 * mutex.  A false-negative does no harm.
+	 */
+	ret = __d_lookup(base, &this);
+	if (ret && unlikely(ret->d_flags & DCACHE_OP_REVALIDATE)) {
+		dput(ret);
+		ret = NULL;
+	}
+	if (ret)
+		return ret;
+
+	mutex_lock(&base->d_inode->i_mutex);
+	ret =  __lookup_hash(&this, base, 0);
+	mutex_unlock(&base->d_inode->i_mutex);
+	return ret;
+}
+EXPORT_SYMBOL(lookup_one_len_unlocked);
+
 int user_path_at_empty(int dfd, const char __user *name, unsigned flags,
 		 struct path *path, int *empty)
 {