linux-kernel - [PATCH v5 11/16] securityfs: Only use simple_pin_fs/simple_release_fs for init_user

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Message-Id: <20211208221818.1519628-12-stefanb@linux.ibm.com>
Date:   Wed,  8 Dec 2021 17:18:13 -0500
From:   Stefan Berger <stefanb@...ux.ibm.com>
To:     linux-integrity@...r.kernel.org
Cc:     zohar@...ux.ibm.com, serge@...lyn.com,
        christian.brauner@...ntu.com, containers@...ts.linux.dev,
        dmitry.kasatkin@...il.com, ebiederm@...ssion.com,
        krzysztof.struczynski@...wei.com, roberto.sassu@...wei.com,
        mpeters@...hat.com, lhinds@...hat.com, lsturman@...hat.com,
        puiterwi@...hat.com, jejb@...ux.ibm.com, jamjoom@...ibm.com,
        linux-kernel@...r.kernel.org, paul@...l-moore.com, rgb@...hat.com,
        linux-security-module@...r.kernel.org, jmorris@...ei.org,
        Stefan Berger <stefanb@...ux.ibm.com>,
        James Bottomley <James.Bottomley@...senPartnership.com>
Subject: [PATCH v5 11/16] securityfs: Only use simple_pin_fs/simple_release_fs for init_user_ns

To prepare for virtualization of SecurityFS, use simple_pin_fs and
simpe_release_fs only when init_user_ns is active.

Signed-off-by: Stefan Berger <stefanb@...ux.ibm.com>
Signed-off-by: James Bottomley <James.Bottomley@...senPartnership.com>
Acked-by: Christian Brauner <christian.brauner@...ntu.com>
---
 security/inode.c | 32 +++++++++++++++++++++++---------
 1 file changed, 23 insertions(+), 9 deletions(-)

diff --git a/security/inode.c b/security/inode.c
index 6c326939750d..9ba2fa875c4c 100644
--- a/security/inode.c
+++ b/security/inode.c
@@ -21,9 +21,10 @@
 #include <linux/security.h>
 #include <linux/lsm_hooks.h>
 #include <linux/magic.h>
+#include <linux/user_namespace.h>
 
-static struct vfsmount *mount;
-static int mount_count;
+static struct vfsmount *init_securityfs_mount;
+static int init_securityfs_mount_count;
 
 static void securityfs_free_inode(struct inode *inode)
 {
@@ -109,6 +110,7 @@ static struct dentry *securityfs_create_dentry(const char *name, umode_t mode,
 					const struct file_operations *fops,
 					const struct inode_operations *iops)
 {
+	struct user_namespace *ns = current_user_ns();
 	struct dentry *dentry;
 	struct inode *dir, *inode;
 	int error;
@@ -118,12 +120,19 @@ static struct dentry *securityfs_create_dentry(const char *name, umode_t mode,
 
 	pr_debug("securityfs: creating file '%s'\n",name);
 
-	error = simple_pin_fs(&fs_type, &mount, &mount_count);
-	if (error)
-		return ERR_PTR(error);
+	if (ns == &init_user_ns) {
+		error = simple_pin_fs(&fs_type, &init_securityfs_mount,
+				      &init_securityfs_mount_count);
+		if (error)
+			return ERR_PTR(error);
+	}
 
-	if (!parent)
-		parent = mount->mnt_root;
+	if (!parent) {
+		if (ns == &init_user_ns)
+			parent = init_securityfs_mount->mnt_root;
+		else
+			return ERR_PTR(-EINVAL);
+	}
 
 	dir = d_inode(parent);
 
@@ -168,7 +177,9 @@ static struct dentry *securityfs_create_dentry(const char *name, umode_t mode,
 	dentry = ERR_PTR(error);
 out:
 	inode_unlock(dir);
-	simple_release_fs(&mount, &mount_count);
+	if (ns == &init_user_ns)
+		simple_release_fs(&init_securityfs_mount,
+				  &init_securityfs_mount_count);
 	return dentry;
 }
 
@@ -294,6 +305,7 @@ EXPORT_SYMBOL_GPL(securityfs_create_symlink);
  */
 void securityfs_remove(struct dentry *dentry)
 {
+	struct user_namespace *ns = dentry->d_sb->s_user_ns;
 	struct inode *dir;
 
 	if (!dentry || IS_ERR(dentry))
@@ -309,7 +321,9 @@ void securityfs_remove(struct dentry *dentry)
 		dput(dentry);
 	}
 	inode_unlock(dir);
-	simple_release_fs(&mount, &mount_count);
+	if (ns == &init_user_ns)
+		simple_release_fs(&init_securityfs_mount,
+				  &init_securityfs_mount_count);
 }
 EXPORT_SYMBOL_GPL(securityfs_remove);
 
-- 
2.31.1