linux-kernel - [RFC PATCH v9 04/16] security: add new securityfs delete function

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Date:   Mon, 30 Jan 2023 14:57:19 -0800
From:   Fan Wu <wufan@...ux.microsoft.com>
To:     corbet@....net, zohar@...ux.ibm.com, jmorris@...ei.org,
        serge@...lyn.com, tytso@....edu, ebiggers@...nel.org,
        axboe@...nel.dk, agk@...hat.com, snitzer@...nel.org,
        eparis@...hat.com, paul@...l-moore.com
Cc:     linux-doc@...r.kernel.org, linux-integrity@...r.kernel.org,
        linux-security-module@...r.kernel.org,
        linux-fscrypt@...r.kernel.org, linux-block@...r.kernel.org,
        dm-devel@...hat.com, linux-audit@...hat.com,
        roberto.sassu@...wei.com, linux-kernel@...r.kernel.org,
        Fan Wu <wufan@...ux.microsoft.com>
Subject: [RFC PATCH v9 04/16] security: add new securityfs delete function

When deleting a directory in the security file system, the existing
securityfs_remove requires the directory to be empty, otherwise
it will do nothing. This leads to a potential risk that the security
file system might be in an unclean state when the intentded deletion
did not happen.

This commit introduces a new function securityfs_recursive_remove
to recursively delete a directory without leaving an unclean state.

Co-developed-by: Christian Brauner (Microsoft) <brauner@...nel.org>
Signed-off-by: Fan Wu <wufan@...ux.microsoft.com>

---
v1-v8:
  + Not present
---
 include/linux/security.h |  1 +
 security/inode.c         | 25 +++++++++++++++++++++++++
 2 files changed, 26 insertions(+)

diff --git a/include/linux/security.h b/include/linux/security.h
index 5b67f208f7de..479e154a12b8 100644
--- a/include/linux/security.h
+++ b/include/linux/security.h
@@ -1985,6 +1985,7 @@ struct dentry *securityfs_create_symlink(const char *name,
 					 const char *target,
 					 const struct inode_operations *iops);
 extern void securityfs_remove(struct dentry *dentry);
+extern void securityfs_recursive_remove(struct dentry *dentry);
 
 #else /* CONFIG_SECURITYFS */
 
diff --git a/security/inode.c b/security/inode.c
index 6c326939750d..13358e8547e8 100644
--- a/security/inode.c
+++ b/security/inode.c
@@ -313,6 +313,31 @@ void securityfs_remove(struct dentry *dentry)
 }
 EXPORT_SYMBOL_GPL(securityfs_remove);
 
+static void remove_one(struct dentry *victim)
+{
+	simple_release_fs(&mount, &mount_count);
+}
+
+/**
+ * securityfs_recursive_remove - recursively removes a file or directory from the securityfs filesystem
+ *
+ * @dentry: a pointer to a the dentry of the file or directory to be removed.
+ *
+ * This function recursively removes a file or directory in securityfs that was
+ * previously created with a call to another securityfs function (like
+ * securityfs_create_file() or variants thereof.)
+ */
+void securityfs_recursive_remove(struct dentry *dentry)
+{
+	if (IS_ERR_OR_NULL(dentry))
+		return;
+
+	simple_pin_fs(&fs_type, &mount, &mount_count);
+	simple_recursive_removal(dentry, remove_one);
+	simple_release_fs(&mount, &mount_count);
+}
+EXPORT_SYMBOL_GPL(securityfs_recursive_remove);
+
 #ifdef CONFIG_SECURITY
 static struct dentry *lsm_dentry;
 static ssize_t lsm_read(struct file *filp, char __user *buf, size_t count,
-- 
2.39.0