Re: [PATCH v5 1/3] Add a new LSM-supporting anonymous inode interface

[Eric Biggers]

On Wed, Apr 01, 2020 at 02:39:01PM -0700, Daniel Colascione wrote:
> This change adds two new functions, anon_inode_getfile_secure and
> anon_inode_getfd_secure, that create anonymous-node files with
> individual non-S_PRIVATE inodes to which security modules can apply
> policy. Existing callers continue using the original singleton-inode
> kind of anonymous-inode file. We can transition anonymous inode users
> to the new kind of anonymous inode in individual patches for the sake
> of bisection and review.
> 
> The new functions accept an optional context_inode parameter that
> callers can use to provide additional contextual information to
> security modules, e.g., indicating that one anonymous struct file is a
> logical child of another, allowing a security model to propagate
> security information from one to the other.
> 
> Signed-off-by: Daniel Colascione <dancol@xxxxxxxxxx>
> ---
>  fs/anon_inodes.c            | 191 ++++++++++++++++++++++++++++--------
>  include/linux/anon_inodes.h |  13 +++
>  include/linux/lsm_hooks.h   |  11 +++
>  include/linux/security.h    |   3 +
>  security/security.c         |   9 ++
>  5 files changed, 186 insertions(+), 41 deletions(-)
> 
> diff --git a/fs/anon_inodes.c b/fs/anon_inodes.c
> index 89714308c25b..f87f221167cf 100644
> --- a/fs/anon_inodes.c
> +++ b/fs/anon_inodes.c
> @@ -55,61 +55,108 @@ static struct file_system_type anon_inode_fs_type = {
>  	.kill_sb	= kill_anon_super,
>  };
>  
> -/**
> - * anon_inode_getfile - creates a new file instance by hooking it up to an
> - *                      anonymous inode, and a dentry that describe the "class"
> - *                      of the file
> - *
> - * @name:    [in]    name of the "class" of the new file
> - * @fops:    [in]    file operations for the new file
> - * @priv:    [in]    private data for the new file (will be file's private_data)
> - * @flags:   [in]    flags
> - *
> - * Creates a new file by hooking it on a single inode. This is useful for files
> - * that do not need to have a full-fledged inode in order to operate correctly.
> - * All the files created with anon_inode_getfile() will share a single inode,
> - * hence saving memory and avoiding code duplication for the file/inode/dentry
> - * setup.  Returns the newly created file* or an error pointer.
> - */
> -struct file *anon_inode_getfile(const char *name,
> -				const struct file_operations *fops,
> -				void *priv, int flags)
> +static struct inode *anon_inode_make_secure_inode(
> +	const char *name,
> +	const struct inode *context_inode)
> +{
> +	struct inode *inode;
> +	const struct qstr qname = QSTR_INIT(name, strlen(name));
> +	int error;
> +
> +	inode = alloc_anon_inode(anon_inode_mnt->mnt_sb);
> +	if (IS_ERR(inode))
> +		return inode;
> +	inode->i_flags &= ~S_PRIVATE;
> +	error =	security_inode_init_security_anon(
> +		inode, &qname, context_inode);
> +	if (error) {
> +		iput(inode);
> +		return ERR_PTR(error);
> +	}
> +	return inode;
> +}
> +
> +struct file *_anon_inode_getfile(const char *name,
> +				 const struct file_operations *fops,
> +				 void *priv, int flags,
> +				 const struct inode *context_inode,
> +				 bool secure)

Unnecessarily global function.

>  {
> +	struct inode *inode;
>  	struct file *file;
>  
> -	if (IS_ERR(anon_inode_inode))
> -		return ERR_PTR(-ENODEV);
> +	if (secure) {
> +		inode =	anon_inode_make_secure_inode(
> +			name, context_inode);
> +		if (IS_ERR(inode))
> +			return ERR_PTR(PTR_ERR(inode));

Use ERR_CAST(), not ERR_PTR(PTR_ERR()).

>  /**
> - * anon_inode_getfd - creates a new file instance by hooking it up to an
> - *                    anonymous inode, and a dentry that describe the "class"
> - *                    of the file
> + * anon_inode_getfile_secure - creates a new file instance by hooking
> + *                             it up to a new anonymous inode and a
> + *                             dentry that describe the "class" of the
> + *                             file.  Make it possible to use security
> + *                             modules to control access to the
> + *                             new file.
> + *
> + * @name:    [in]    name of the "class" of the new file
> + * @fops:    [in]    file operations for the new file
> + * @priv:    [in]    private data for the new file (will be file's private_data)
> + * @flags:   [in]    flags
> + *
> + * Creates a new file by hooking it on an unspecified inode. This is
> + * useful for files that do not need to have a full-fledged filesystem
> + * to operate correctly.  All the files created with
> + * anon_inode_getfile_secure() will have distinct inodes, avoiding
> + * code duplication for the file/inode/dentry setup.  Returns the
> + * newly created file* or an error pointer.
> + */
> +struct file *anon_inode_getfile_secure(const char *name,
> +				       const struct file_operations *fops,
> +				       void *priv, int flags,
> +				       const struct inode *context_inode)

Why copy-and-paste this long comment if it's not even updated to document the
new argument?

> diff --git a/include/linux/lsm_hooks.h b/include/linux/lsm_hooks.h
> index 20d8cf194fb7..5434c1d285b2 100644
> --- a/include/linux/lsm_hooks.h
> +++ b/include/linux/lsm_hooks.h
> @@ -215,6 +215,13 @@
>   *	Returns 0 if @name and @value have been successfully set,
>   *	-EOPNOTSUPP if no security attribute is needed, or
>   *	-ENOMEM on memory allocation failure.
> + * @inode_init_security_anon:
> + *      Set up a secure anonymous inode.
> + *      @inode contains the inode structure
> + *      @name name of the anonymous inode class
> + *      @context_inode optional related inode
> + *	Returns 0 on success. Returns -EPERM if	the security module denies
> + *	the creation of this inode.

Shouldn't it be EACCES?