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From:   Greg Kroah-Hartman <gregkh@linuxfoundation.org>
To:     linux-kernel@vger.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        stable@vger.kernel.org, stable <stable@kernel.org>,
        Kuyo Chang <kuyo.chang@mediatek.com>
Subject: [PATCH 5.4 081/108] debugfs: add debugfs_lookup_and_remove()
Date:   Tue, 13 Sep 2022 16:06:52 +0200
Message-Id: <20220913140357.110806115@linuxfoundation.org>
In-Reply-To: <20220913140353.549108748@linuxfoundation.org>
References: <20220913140353.549108748@linuxfoundation.org>
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From: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

commit dec9b2f1e0455a151a7293c367da22ab973f713e upstream.

There is a very common pattern of using
debugfs_remove(debufs_lookup(..)) which results in a dentry leak of the
dentry that was looked up.  Instead of having to open-code the correct
pattern of calling dput() on the dentry, create
debugfs_lookup_and_remove() to handle this pattern automatically and
properly without any memory leaks.

Cc: stable <stable@kernel.org>
Reported-by: Kuyo Chang <kuyo.chang@mediatek.com>
Tested-by: Kuyo Chang <kuyo.chang@mediatek.com>
Link: https://lore.kernel.org/r/YxIaQ8cSinDR881k@kroah.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
 fs/debugfs/inode.c      |   22 ++++++++++++++++++++++
 include/linux/debugfs.h |    6 ++++++
 2 files changed, 28 insertions(+)

--- a/fs/debugfs/inode.c
+++ b/fs/debugfs/inode.c
@@ -743,6 +743,28 @@ void debugfs_remove(struct dentry *dentr
 EXPORT_SYMBOL_GPL(debugfs_remove);
 
 /**
+ * debugfs_lookup_and_remove - lookup a directory or file and recursively remove it
+ * @name: a pointer to a string containing the name of the item to look up.
+ * @parent: a pointer to the parent dentry of the item.
+ *
+ * This is the equlivant of doing something like
+ * debugfs_remove(debugfs_lookup(..)) but with the proper reference counting
+ * handled for the directory being looked up.
+ */
+void debugfs_lookup_and_remove(const char *name, struct dentry *parent)
+{
+	struct dentry *dentry;
+
+	dentry = debugfs_lookup(name, parent);
+	if (!dentry)
+		return;
+
+	debugfs_remove(dentry);
+	dput(dentry);
+}
+EXPORT_SYMBOL_GPL(debugfs_lookup_and_remove);
+
+/**
  * debugfs_remove_recursive - recursively removes a directory
  * @dentry: a pointer to a the dentry of the directory to be removed.  If this
  *          parameter is NULL or an error value, nothing will be done.
--- a/include/linux/debugfs.h
+++ b/include/linux/debugfs.h
@@ -85,6 +85,8 @@ struct dentry *debugfs_create_automount(
 void debugfs_remove(struct dentry *dentry);
 void debugfs_remove_recursive(struct dentry *dentry);
 
+void debugfs_lookup_and_remove(const char *name, struct dentry *parent);
+
 const struct file_operations *debugfs_real_fops(const struct file *filp);
 
 int debugfs_file_get(struct dentry *dentry);
@@ -216,6 +218,10 @@ static inline void debugfs_remove(struct
 static inline void debugfs_remove_recursive(struct dentry *dentry)
 { }
 
+static inline void debugfs_lookup_and_remove(const char *name,
+					     struct dentry *parent)
+{ }
+
 const struct file_operations *debugfs_real_fops(const struct file *filp);
 
 static inline int debugfs_file_get(struct dentry *dentry)