[PATCH v5 13/23] security: Introduce file_pre_free_security hook

[Paul Moore]

On Nov  7, 2023 Roberto Sassu <roberto.sassu at huaweicloud.com> wrote:
> 
> In preparation for moving IMA and EVM to the LSM infrastructure, introduce
> the file_pre_free_security hook.
> 
> IMA calculates at file close the new digest of the file content and writes
> it to security.ima, so that appraisal at next file access succeeds.
> 
> LSMs could also take some action before the last reference of a file is
> released.
> 
> The new hook cannot return an error and cannot cause the operation to be
> reverted.
> 
> Signed-off-by: Roberto Sassu <roberto.sassu at huawei.com>
> Acked-by: Casey Schaufler <casey at schaufler-ca.com>
> Reviewed-by: Mimi Zohar <zohar at linux.ibm.com>
> ---
>  fs/file_table.c               |  1 +
>  include/linux/lsm_hook_defs.h |  1 +
>  include/linux/security.h      |  4 ++++
>  security/security.c           | 11 +++++++++++
>  4 files changed, 17 insertions(+)
> 
> diff --git a/fs/file_table.c b/fs/file_table.c
> index de4a2915bfd4..64ed74555e64 100644
> --- a/fs/file_table.c
> +++ b/fs/file_table.c
> @@ -385,6 +385,7 @@ static void __fput(struct file *file)
>  	eventpoll_release(file);
>  	locks_remove_file(file);
>  
> +	security_file_pre_free(file);

I worry that security_file_pre_free() is a misleading name as "free"
tends to imply memory management tasks, which isn't the main focus of
this hook.  What do you think of security_file_release() or
security_file_put() instead?

>  	ima_file_free(file);
>  	if (unlikely(file->f_flags & FASYNC)) {
>  		if (file->f_op->fasync)

--
paul-moore.com