linux-kernel - Re: [PATCH v3 1/3] Add a new LSM-supporting anonymous inode interface

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Message-ID: <d2d79bba-2401-9c09-ef4d-4dae667ea730@tycho.nsa.gov>
Date:   Thu, 26 Mar 2020 15:00:12 -0400
From:   Stephen Smalley <sds@...ho.nsa.gov>
To:     Daniel Colascione <dancol@...gle.com>, timmurray@...gle.com,
        selinux@...r.kernel.org, linux-security-module@...r.kernel.org,
        linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org,
        kvm@...r.kernel.org, viro@...iv.linux.org.uk, paul@...l-moore.com,
        nnk@...gle.com, lokeshgidra@...gle.com, jmorris@...ei.org
Subject: Re: [PATCH v3 1/3] Add a new LSM-supporting anonymous inode interface

On 3/26/20 2:14 PM, 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@...gle.com>
> ---

Repeating verbatim what I said on v2 of patch 1/3.

> diff --git a/fs/anon_inodes.c b/fs/anon_inodes.c
> index 89714308c25b..114a04fc1db4 100644
> --- a/fs/anon_inodes.c
> +++ b/fs/anon_inodes.c
> @@ -55,75 +55,135 @@ 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,
> +	const struct file_operations *fops)
> +{
> +	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 ERR_PTR(PTR_ERR(inode));

Just return inode here ?

> +	inode->i_flags &= ~S_PRIVATE;
> +	error =	security_inode_init_security_anon(
> +		inode, &qname, fops, context_inode);

Would drop fops argument until we have a real user for it; we can always 
add it later.

> diff --git a/fs/userfaultfd.c b/fs/userfaultfd.c
> index 37df7c9eedb1..07b0f6e03849 100644
> --- a/fs/userfaultfd.c
> +++ b/fs/userfaultfd.c
> @@ -1014,8 +1014,6 @@ static __poll_t userfaultfd_poll(struct file *file, poll_table *wait)
>   	}
>   }
>   
> -static const struct file_operations userfaultfd_fops;
> -
>   static int resolve_userfault_fork(struct userfaultfd_ctx *ctx,
>   				  struct userfaultfd_ctx *new,
>   				  struct uffd_msg *msg)
> @@ -1920,7 +1918,7 @@ static void userfaultfd_show_fdinfo(struct seq_file *m, struct file *f)
>   }
>   #endif
>   
> -static const struct file_operations userfaultfd_fops = {
> +const struct file_operations userfaultfd_fops = {
>   #ifdef CONFIG_PROC_FS
>   	.show_fdinfo	= userfaultfd_show_fdinfo,
>   #endif

These changes are unnecessary for this patch and reverted by patch 3, so 
drop them here.