Re: [PATCH v2 3/6] bpf-lsm: Introduce new helper bpf_ima_file_hash()

[Yonghong Song <yhs@fb.com>]

On 2/15/22 4:40 AM, Roberto Sassu wrote:
> ima_file_hash() has been modified to calculate the measurement of a file on
> demand, if it has not been already performed by IMA. For compatibility
> reasons, ima_inode_hash() remains unchanged.
> 
> Keep the same approach in eBPF and introduce the new helper
> bpf_ima_file_hash() to take advantage of the modified behavior of
> ima_file_hash().
> 
> Signed-off-by: Roberto Sassu <roberto.sassu@huawei.com>
> ---
>   include/uapi/linux/bpf.h       | 11 +++++++++++
>   kernel/bpf/bpf_lsm.c           | 20 ++++++++++++++++++++
>   tools/include/uapi/linux/bpf.h | 11 +++++++++++
>   3 files changed, 42 insertions(+)
> 
> diff --git a/include/uapi/linux/bpf.h b/include/uapi/linux/bpf.h
> index b0383d371b9a..ba33d5718d6b 100644
> --- a/include/uapi/linux/bpf.h
> +++ b/include/uapi/linux/bpf.h
> @@ -4648,6 +4648,16 @@ union bpf_attr {
>    *		**-EOPNOTSUP** if IMA is disabled or **-EINVAL** if
>    *		invalid arguments are passed.
>    *
> + * long bpf_ima_file_hash(struct file *file, void *dst, u32 size)
> + *	Description
> + *		Returns a calculated IMA hash of the *file*.
> + *		If the hash is larger than *size*, then only *size*
> + *		bytes will be copied to *dst*
> + *	Return
> + *		The **hash_algo** is returned on success,
> + *		**-EOPNOTSUP** if the hash calculation failed or **-EINVAL** if
> + *		invalid arguments are passed.
> + *
>    * struct socket *bpf_sock_from_file(struct file *file)
>    *	Description
>    *		If the given file represents a socket, returns the associated
> @@ -5182,6 +5192,7 @@ union bpf_attr {
>   	FN(bprm_opts_set),		\
>   	FN(ktime_get_coarse_ns),	\
>   	FN(ima_inode_hash),		\
> +	FN(ima_file_hash),		\

Please put the above FN(ima_file_hash) to the end of the list.
Otherwise, we have a backward compatability issue.

>   	FN(sock_from_file),		\
>   	FN(check_mtu),			\
>   	FN(for_each_map_elem),		\
> diff --git a/kernel/bpf/bpf_lsm.c b/kernel/bpf/bpf_lsm.c
> index 9e4ecc990647..e8d27af5bbcc 100644
> --- a/kernel/bpf/bpf_lsm.c
> +++ b/kernel/bpf/bpf_lsm.c
[...]