Re: [PATCH 1/2] fs: Provide function that allocates a secure anonymous inode

[Mike Rapoport]

(added Paul Moore for selinux bits)

On Mon, Jun 02, 2025 at 12:17:54PM -0700, Ackerley Tng wrote:
> The new function, alloc_anon_secure_inode(), returns an inode after
> running checks in security_inode_init_security_anon().
> 
> Also refactor secretmem's file creation process to use the new
> function.
> 
> Suggested-by: David Hildenbrand <david@xxxxxxxxxx>
> Signed-off-by: Ackerley Tng <ackerleytng@xxxxxxxxxx>
> ---
>  fs/anon_inodes.c   | 22 ++++++++++++++++------
>  include/linux/fs.h |  1 +
>  mm/secretmem.c     |  9 +--------
>  3 files changed, 18 insertions(+), 14 deletions(-)
> 
> diff --git a/fs/anon_inodes.c b/fs/anon_inodes.c
> index 583ac81669c2..4c3110378647 100644
> --- a/fs/anon_inodes.c
> +++ b/fs/anon_inodes.c
> @@ -55,17 +55,20 @@ static struct file_system_type anon_inode_fs_type = {
>  	.kill_sb	= kill_anon_super,
>  };
> 
> -static struct inode *anon_inode_make_secure_inode(
> -	const char *name,
> -	const struct inode *context_inode)
> +static struct inode *anon_inode_make_secure_inode(struct super_block *s,
> +		const char *name, const struct inode *context_inode,
> +		bool fs_internal)
>  {
>  	struct inode *inode;
>  	int error;
> 
> -	inode = alloc_anon_inode(anon_inode_mnt->mnt_sb);
> +	inode = alloc_anon_inode(s);
>  	if (IS_ERR(inode))
>  		return inode;
> -	inode->i_flags &= ~S_PRIVATE;
> +
> +	if (!fs_internal)
> +		inode->i_flags &= ~S_PRIVATE;
> +
>  	error =	security_inode_init_security_anon(inode, &QSTR(name),
>  						  context_inode);
>  	if (error) {
> @@ -75,6 +78,12 @@ static struct inode *anon_inode_make_secure_inode(
>  	return inode;
>  }
> 
> +struct inode *alloc_anon_secure_inode(struct super_block *s, const char *name)
> +{
> +	return anon_inode_make_secure_inode(s, name, NULL, true);
> +}
> +EXPORT_SYMBOL_GPL(alloc_anon_secure_inode);
> +
>  static struct file *__anon_inode_getfile(const char *name,
>  					 const struct file_operations *fops,
>  					 void *priv, int flags,
> @@ -88,7 +97,8 @@ static struct file *__anon_inode_getfile(const char *name,
>  		return ERR_PTR(-ENOENT);
> 
>  	if (make_inode) {
> -		inode =	anon_inode_make_secure_inode(name, context_inode);
> +		inode = anon_inode_make_secure_inode(anon_inode_mnt->mnt_sb,
> +						     name, context_inode, false);
>  		if (IS_ERR(inode)) {
>  			file = ERR_CAST(inode);
>  			goto err;
> diff --git a/include/linux/fs.h b/include/linux/fs.h
> index 016b0fe1536e..0fded2e3c661 100644
> --- a/include/linux/fs.h
> +++ b/include/linux/fs.h
> @@ -3550,6 +3550,7 @@ extern int simple_write_begin(struct file *file, struct address_space *mapping,
>  extern const struct address_space_operations ram_aops;
>  extern int always_delete_dentry(const struct dentry *);
>  extern struct inode *alloc_anon_inode(struct super_block *);
> +extern struct inode *alloc_anon_secure_inode(struct super_block *, const char *);
>  extern int simple_nosetlease(struct file *, int, struct file_lease **, void **);
>  extern const struct dentry_operations simple_dentry_operations;
> 
> diff --git a/mm/secretmem.c b/mm/secretmem.c
> index 1b0a214ee558..c0e459e58cb6 100644
> --- a/mm/secretmem.c
> +++ b/mm/secretmem.c
> @@ -195,18 +195,11 @@ static struct file *secretmem_file_create(unsigned long flags)
>  	struct file *file;
>  	struct inode *inode;
>  	const char *anon_name = "[secretmem]";
> -	int err;
> 
> -	inode = alloc_anon_inode(secretmem_mnt->mnt_sb);
> +	inode = alloc_anon_secure_inode(secretmem_mnt->mnt_sb, anon_name);
>  	if (IS_ERR(inode))
>  		return ERR_CAST(inode);

I don't think we should not hide secretmem and guest_memfd inodes from
selinux, so clearing S_PRIVATE for them is not needed and you can just drop
fs_internal parameter in anon_inode_make_secure_inode() 

> 
> -	err = security_inode_init_security_anon(inode, &QSTR(anon_name), NULL);
> -	if (err) {
> -		file = ERR_PTR(err);
> -		goto err_free_inode;
> -	}
> -
>  	file = alloc_file_pseudo(inode, secretmem_mnt, "secretmem",
>  				 O_RDWR, &secretmem_fops);
>  	if (IS_ERR(file))
> --
> 2.49.0.1204.g71687c7c1d-goog

-- 
Sincerely yours,
Mike.