On Fri, 25 Apr 2025 18:06:32 -0400, Paul Moore wrote:
On Fri, Apr 25, 2025 at 5:25 AM alexjlzheng@gmail.com wrote:
From: Jinliang Zheng alexjlzheng@tencent.com
Consider the following module code:
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!
Thank you for your reply. :)
A quick procedural note, and you may have gotten an email about this from the stable kernel folks already, you generally shouldn't add the stable alias to your emails directly. You may want to look at the kernel docs on the stable kernel if you haven't already:
Sorry for that, I will read it. And thank you for your pointing it out.
Beyond that, we don't currently support dynamically loading or unloading LSMs so the immediate response to the reproducer above is "don't do that, we don't support it" :) However, if you see a similar problem with a LSM properly registered with the running kernel please let us know.
I don't think that not supporting dynamic loading/unloading of LSMs means that directories/files under securityfs cannot be dynamically added/deleted.
The example code in the commit message is just to quickly show the problem, not the actual usage scenario.
I'm not sure whether existing LSMs have dynamic addition/deletion of files, but I don't think we should prohibit these operations.
Moreover, since securityfs provides the securityfs_remove() interface, it is necessary to handle the deletion of dentry whenever it is used. What's more, we have EXPORT_SYMBOL_GPL(securityfs_remove).
(By the way, the reason why I noticed this problem is because I needed to dynamically create/delete configuration directories/files when implementing an LSM. Of course, I am not dynamically loading/unloading LSM, but dynamically adding/deleting directories/files under securityfs according to the status during LSM operation.)
Therefore, I think we need this patch and strongly recommend it. At least, it has no harm. Hahahaha
thanks, Jinliang Zheng :)
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@tencent.com Cc: stable@vger.kernel.org
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
-- paul-moore.com