Re: [PATCH v5 16/23] security: Introduce inode_post_set_acl hook

[Paul Moore <paul@paul-moore.com>]

On Nov  7, 2023 Roberto Sassu <roberto.sassu@huaweicloud.com> wrote:
> 
> In preparation for moving IMA and EVM to the LSM infrastructure, introduce
> the inode_post_set_acl hook.
> 
> At inode_set_acl hook, EVM verifies the file's existing HMAC value. At
> inode_post_set_acl, EVM re-calculates the file's HMAC based on the modified
> POSIX ACL and other file metadata.
> 
> Other LSMs could similarly take some action after successful POSIX ACL
> change.
> 
> The new hook cannot return an error and cannot cause the operation to be
> reverted.
> 
> Signed-off-by: Roberto Sassu <roberto.sassu@huawei.com>
> Reviewed-by: Stefan Berger <stefanb@linux.ibm.com>
> Acked-by: Casey Schaufler <casey@schaufler-ca.com>
> Reviewed-by: Mimi Zohar <zohar@linux.ibm.com>
> ---
>  fs/posix_acl.c                |  1 +
>  include/linux/lsm_hook_defs.h |  2 ++
>  include/linux/security.h      |  7 +++++++
>  security/security.c           | 17 +++++++++++++++++
>  4 files changed, 27 insertions(+)

...

> diff --git a/security/security.c b/security/security.c
> index ca650c285fd9..d2dbea54a63a 100644
> --- a/security/security.c
> +++ b/security/security.c
> @@ -2350,6 +2350,23 @@ int security_inode_set_acl(struct mnt_idmap *idmap,
>  	return evm_inode_set_acl(idmap, dentry, acl_name, kacl);
>  }
>  
> +/**
> + * security_inode_post_set_acl() - Update inode security from posix acls set
> + * @dentry: file
> + * @acl_name: acl name
> + * @kacl: acl struct
> + *
> + * Update inode security data after successfully setting posix acls on @dentry.
> + * The posix acls in @kacl are identified by @acl_name.
> + */
> +void security_inode_post_set_acl(struct dentry *dentry, const char *acl_name,
> +				 struct posix_acl *kacl)
> +{
> +	if (unlikely(IS_PRIVATE(d_backing_inode(dentry))))
> +		return;

Another case where the existing evm_inode_post_set_acl() hook doesn't
check S_PRIVATE but this hook does.

> +	call_void_hook(inode_post_set_acl, dentry, acl_name, kacl);
> +}
> +
>  /**
>   * security_inode_get_acl() - Check if reading posix acls is allowed
>   * @idmap: idmap of the mount
> -- 
> 2.34.1

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