[PATCH v2] securityfs: fix missing of d_delete() in securityfs_remove()

[alexjlzheng at gmail.com]

From: Jinliang Zheng <alexjlzheng at tencent.com>

Consider the following module code (just an example to make it easier to
illustrate the problem, in fact the LSM module will not be dynamically
unloaded):

  static struct dentry *dentry;

  static int __init securityfs_test_init(void)
  {
          dentry = securityfs_create_dir("standon", NULL);
          return PTR_ERR(dentry);
  }

  static void __exit securityfs_test_exit(void)
  {
          securityfs_remove(dentry);
  }

  module_init(securityfs_test_init);
  module_exit(securityfs_test_exit);

and then:

  insmod /path/to/thismodule
  cd /sys/kernel/security/standon     <- we hold 'standon'
  rmmod thismodule                    <- 'standon' don't go away
  insmod /path/to/thismodule          <- Failed: File exists!

Although the LSM module will not be dynamically added or deleted after
the kernel is started, it may dynamically add or delete pseudo files
for status export or function configuration in userspace according to
different status, which we are not prohibited from doing so.

In addition, securityfs_recursive_remove() avoids this problem by calling
__d_drop() directly. As a non-recursive version, it is somewhat strange
that securityfs_remove() does not clean up the deleted dentry.

Fix this by adding d_delete() in securityfs_remove().

Fixes: b67dbf9d4c198 ("[PATCH] add securityfs for all LSMs to use")
Signed-off-by: Jinliang Zheng <alexjlzheng at tencent.com>
---
changelog:
v2: Modify the commit message to make it clearer
v1: https://lore.kernel.org/all/20250426150931.2840-1-alexjlzheng@tencent.com/
---
 security/inode.c | 1 +
 1 file changed, 1 insertion(+)

diff --git a/security/inode.c b/security/inode.c
index da3ab44c8e57..d99baf26350a 100644
--- a/security/inode.c
+++ b/security/inode.c
@@ -306,6 +306,7 @@ void securityfs_remove(struct dentry *dentry)
 			simple_rmdir(dir, dentry);
 		else
 			simple_unlink(dir, dentry);
+		d_delete(dentry);
 		dput(dentry);
 	}
 	inode_unlock(dir);
-- 
2.49.0