Re: [PATCH v5 17/23] security: Introduce inode_post_remove_acl hook

[Paul Moore]

On Nov  7, 2023 Roberto Sassu <roberto.sassu@xxxxxxxxxxxxxxx> wrote:
> 
> In preparation for moving IMA and EVM to the LSM infrastructure, introduce
> the inode_post_remove_acl hook.
> 
> At inode_remove_acl hook, EVM verifies the file's existing HMAC value. At
> inode_post_remove_acl, EVM re-calculates the file's HMAC with the passed
> POSIX ACL removed and other file metadata.
> 
> Other LSMs could similarly take some action after successful POSIX ACL
> removal.
> 
> The new hook cannot return an error and cannot cause the operation to be
> reverted.
> 
> Signed-off-by: Roberto Sassu <roberto.sassu@xxxxxxxxxx>
> Reviewed-by: Stefan Berger <stefanb@xxxxxxxxxxxxx>
> Acked-by: Casey Schaufler <casey@xxxxxxxxxxxxxxxx>
> Reviewed-by: Mimi Zohar <zohar@xxxxxxxxxxxxx>
> ---
>  fs/posix_acl.c                |  1 +
>  include/linux/lsm_hook_defs.h |  2 ++
>  include/linux/security.h      |  8 ++++++++
>  security/security.c           | 17 +++++++++++++++++
>  4 files changed, 28 insertions(+)

...

> diff --git a/security/security.c b/security/security.c
> index d2dbea54a63a..6eb7c9cff1e5 100644
> --- a/security/security.c
> +++ b/security/security.c
> @@ -2413,6 +2413,23 @@ int security_inode_remove_acl(struct mnt_idmap *idmap,
>  	return evm_inode_remove_acl(idmap, dentry, acl_name);
>  }
>  
> +/**
> + * security_inode_post_remove_acl() - Update inode security after rm posix acls
> + * @idmap: idmap of the mount
> + * @dentry: file
> + * @acl_name: acl name
> + *
> + * Update inode security data after successfully removing posix acls on
> + * @dentry in @idmap. The posix acls are identified by @acl_name.
> + */
> +void security_inode_post_remove_acl(struct mnt_idmap *idmap,
> +				    struct dentry *dentry, const char *acl_name)
> +{
> +	if (unlikely(IS_PRIVATE(d_backing_inode(dentry))))
> +		return;

See previous comments regaring S_PRIVATE checks.

> +	call_void_hook(inode_post_remove_acl, idmap, dentry, acl_name);
> +}
> +
>  /**
>   * security_inode_post_setxattr() - Update the inode after a setxattr operation
>   * @dentry: file
> -- 
> 2.34.1

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