[PATCH v5 11/16] securityfs: Only use simple_pin_fs/simple_release_fs for init_user_ns

Stefan Berger
2021-12-08T22:18:45Z

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@linux.ibm.com>
Signed-off-by: James Bottomley <James.Bottomley@HansenPartnership.com>
Acked-by: Christian Brauner <christian.brauner@ubuntu.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