[PATCH v9 12/25] security: Introduce file_post_open hook

[Christian Brauner]

On Mon, Jan 15, 2024 at 07:17:56PM +0100, Roberto Sassu wrote:
> From: Roberto Sassu <roberto.sassu at huawei.com>
> 
> In preparation to move IMA and EVM to the LSM infrastructure, introduce the
> file_post_open hook. Also, export security_file_post_open() for NFS.
> 
> Based on policy, IMA calculates the digest of the file content and
> extends the TPM with the digest, verifies the file's integrity based on
> the digest, and/or includes the file digest in the audit log.
> 
> LSMs could similarly take action depending on the file content and the
> access mask requested with open().
> 
> The new hook returns a value and can cause the open to be aborted.
> 
> Signed-off-by: Roberto Sassu <roberto.sassu at huawei.com>
> Reviewed-by: Stefan Berger <stefanb at linux.ibm.com>
> Acked-by: Casey Schaufler <casey at schaufler-ca.com>
> Reviewed-by: Mimi Zohar <zohar at linux.ibm.com>
> ---
>  fs/namei.c                    |  2 ++
>  fs/nfsd/vfs.c                 |  6 ++++++
>  include/linux/lsm_hook_defs.h |  1 +
>  include/linux/security.h      |  6 ++++++
>  security/security.c           | 17 +++++++++++++++++
>  5 files changed, 32 insertions(+)
> 
> diff --git a/fs/namei.c b/fs/namei.c
> index 71c13b2990b4..fb93d3e13df6 100644
> --- a/fs/namei.c
> +++ b/fs/namei.c
> @@ -3620,6 +3620,8 @@ static int do_open(struct nameidata *nd,
>  	error = may_open(idmap, &nd->path, acc_mode, open_flag);
>  	if (!error && !(file->f_mode & FMODE_OPENED))
>  		error = vfs_open(&nd->path, file);
> +	if (!error)
> +		error = security_file_post_open(file, op->acc_mode);

What does it do for O_CREAT? IOW, we managed to create that thing and we
managed to open that thing. Can security_file_post_open() and
ima_file_check() fail afterwards even for newly created files?