Re: [PATCH v4 11/16] securityfs: Only use simple_pin_fs/simple_release_fs for init_user_ns

[Christian Brauner <christian.brauner@ubuntu.com>]

On Tue, Dec 07, 2021 at 03:21:22PM -0500, Stefan Berger wrote:
> 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>
> ---
>  security/inode.c | 30 +++++++++++++++++++++---------
>  1 file changed, 21 insertions(+), 9 deletions(-)
> 
> diff --git a/security/inode.c b/security/inode.c
> index 6c326939750d..1a720b2c566d 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 *securityfs_mount;
> +static int 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 +120,17 @@ 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, &securityfs_mount,
> +				      &securityfs_mount_count);
> +		if (error)
> +			return ERR_PTR(error);
> +	}
>  
> -	if (!parent)
> -		parent = mount->mnt_root;
> +	if (!parent) {
> +		if (ns == &init_user_ns)
> +			parent = securityfs_mount->mnt_root;

Wouldn't you want an

		else
			return ERR_PTR(-EINVAL);

in here already?

> +	}
>  
>  	dir = d_inode(parent);
>  
> @@ -168,7 +175,9 @@ 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(&securityfs_mount,
> +				  &securityfs_mount_count);
>  	return dentry;
>  }
>  
> @@ -294,6 +303,7 @@ 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 +319,9 @@ 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(&securityfs_mount,
> +				  &securityfs_mount_count);
>  }
>  EXPORT_SYMBOL_GPL(securityfs_remove);
>  
> -- 
> 2.31.1
> 
>