Re: [PATCH v2 17/25] security: Introduce inode_post_create_tmpfile hook

[Casey Schaufler]

On 8/31/2023 3:41 AM, Roberto Sassu wrote:
> From: Roberto Sassu <roberto.sassu@xxxxxxxxxx>
>
> In preparation for moving IMA and EVM to the LSM infrastructure, introduce
> the inode_post_create_tmpfile hook.

Repeat of new LSM hook general comment:
Would you please include some explanation of how an LSM would use this hook?
You might start with a description of how it is used in IMA/EVM, and why that
could be generally useful.


>
> Signed-off-by: Roberto Sassu <roberto.sassu@xxxxxxxxxx>
> Reviewed-by: Stefan Berger <stefanb@xxxxxxxxxxxxx>
> ---
>  fs/namei.c                    |  1 +
>  include/linux/lsm_hook_defs.h |  2 ++
>  include/linux/security.h      |  8 ++++++++
>  security/security.c           | 18 ++++++++++++++++++
>  4 files changed, 29 insertions(+)
>
> diff --git a/fs/namei.c b/fs/namei.c
> index c8c4ab26b52a..efed0e1e93f5 100644
> --- a/fs/namei.c
> +++ b/fs/namei.c
> @@ -3700,6 +3700,7 @@ static int vfs_tmpfile(struct mnt_idmap *idmap,
>  		inode->i_state |= I_LINKABLE;
>  		spin_unlock(&inode->i_lock);
>  	}
> +	security_inode_post_create_tmpfile(idmap, dir, file, mode);
>  	ima_post_create_tmpfile(idmap, dir, file, mode);
>  	return 0;
>  }
> diff --git a/include/linux/lsm_hook_defs.h b/include/linux/lsm_hook_defs.h
> index b1634b5de98c..9ae573b83737 100644
> --- a/include/linux/lsm_hook_defs.h
> +++ b/include/linux/lsm_hook_defs.h
> @@ -121,6 +121,8 @@ LSM_HOOK(int, 0, inode_init_security_anon, struct inode *inode,
>  	 const struct qstr *name, const struct inode *context_inode)
>  LSM_HOOK(int, 0, inode_create, struct inode *dir, struct dentry *dentry,
>  	 umode_t mode)
> +LSM_HOOK(void, LSM_RET_VOID, inode_post_create_tmpfile, struct mnt_idmap *idmap,
> +	 struct inode *dir, struct file *file, umode_t mode)
>  LSM_HOOK(int, 0, inode_link, struct dentry *old_dentry, struct inode *dir,
>  	 struct dentry *new_dentry)
>  LSM_HOOK(int, 0, inode_unlink, struct inode *dir, struct dentry *dentry)
> diff --git a/include/linux/security.h b/include/linux/security.h
> index f210bd66e939..5f296761883f 100644
> --- a/include/linux/security.h
> +++ b/include/linux/security.h
> @@ -338,6 +338,9 @@ int security_inode_init_security_anon(struct inode *inode,
>  				      const struct qstr *name,
>  				      const struct inode *context_inode);
>  int security_inode_create(struct inode *dir, struct dentry *dentry, umode_t mode);
> +void security_inode_post_create_tmpfile(struct mnt_idmap *idmap,
> +					struct inode *dir, struct file *file,
> +					umode_t mode);
>  int security_inode_link(struct dentry *old_dentry, struct inode *dir,
>  			 struct dentry *new_dentry);
>  int security_inode_unlink(struct inode *dir, struct dentry *dentry);
> @@ -788,6 +791,11 @@ static inline int security_inode_create(struct inode *dir,
>  	return 0;
>  }
>  
> +static inline void
> +security_inode_post_create_tmpfile(struct mnt_idmap *idmap, struct inode *dir,
> +				   struct file *file, umode_t mode)
> +{ }
> +
>  static inline int security_inode_link(struct dentry *old_dentry,
>  				       struct inode *dir,
>  				       struct dentry *new_dentry)
> diff --git a/security/security.c b/security/security.c
> index 56c1c1e66fd1..e5acb11f6ebd 100644
> --- a/security/security.c
> +++ b/security/security.c
> @@ -1920,6 +1920,24 @@ int security_inode_create(struct inode *dir, struct dentry *dentry,
>  }
>  EXPORT_SYMBOL_GPL(security_inode_create);
>  
> +/**
> + * security_inode_post_create_tmpfile() - Update inode security field after creation of tmpfile
> + * @idmap: idmap of the mount
> + * @dir: the inode of the base directory
> + * @file: file descriptor of the new tmpfile
> + * @mode: the mode of the new tmpfile
> + *
> + * Update inode security field after a tmpfile has been created.
> + */
> +void security_inode_post_create_tmpfile(struct mnt_idmap *idmap,
> +					struct inode *dir,
> +					struct file *file, umode_t mode)
> +{
> +	if (unlikely(IS_PRIVATE(dir)))
> +		return;
> +	call_void_hook(inode_post_create_tmpfile, idmap, dir, file, mode);
> +}
> +
>  /**
>   * security_inode_link() - Check if creating a hard link is allowed
>   * @old_dentry: existing file