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Message-ID: <a9336dd5-df17-85d9-7c63-d8ab4b74b459@fb.com>
Date: Fri, 20 Nov 2020 09:47:26 -0800
From: Yonghong Song <yhs@...com>
To: KP Singh <kpsingh@...omium.org>, James Morris <jmorris@...ei.org>,
<linux-kernel@...r.kernel.org>, <bpf@...r.kernel.org>,
<linux-security-module@...r.kernel.org>
CC: Alexei Starovoitov <ast@...nel.org>,
Daniel Borkmann <daniel@...earbox.net>,
Florent Revest <revest@...omium.org>,
Brendan Jackman <jackmanb@...omium.org>,
Mimi Zohar <zohar@...ux.ibm.com>
Subject: Re: [PATCH bpf-next 2/3] bpf: Add a BPF helper for getting the IMA
hash of an inode
On 11/20/20 5:17 AM, KP Singh wrote:
> From: KP Singh <kpsingh@...gle.com>
>
> Provide a wrapper function to get the IMA hash of an inode. This helper
> is useful in fingerprinting files (e.g executables on execution) and
> using these fingerprints in detections like an executable unlinking
> itself.
>
> Since the ima_inode_hash can sleep, it's only allowed for sleepable
> LSM hooks.
>
> Signed-off-by: KP Singh <kpsingh@...gle.com>
> ---
> include/uapi/linux/bpf.h | 11 +++++++++++
> kernel/bpf/bpf_lsm.c | 26 ++++++++++++++++++++++++++
> scripts/bpf_helpers_doc.py | 1 +
> tools/include/uapi/linux/bpf.h | 11 +++++++++++
> 4 files changed, 49 insertions(+)
>
> diff --git a/include/uapi/linux/bpf.h b/include/uapi/linux/bpf.h
> index 3ca6146f001a..dd5b8622bb89 100644
> --- a/include/uapi/linux/bpf.h
> +++ b/include/uapi/linux/bpf.h
> @@ -3807,6 +3807,16 @@ union bpf_attr {
> * See: **clock_gettime**\ (**CLOCK_MONOTONIC_COARSE**)
> * Return
> * Current *ktime*.
> + *
> + * long bpf_ima_inode_hash(struct inode *inode, void *dst, u32 size)
> + * Description
> + * Returns the stored IMA hash of the *inode* (if it's avaialable).
> + * If the hash is larger than *size*, then only *size*
> + * bytes will be copied to *dst*
> + * Return > + * The **hash_algo** of is returned on success,
of => if?
> + * **-EOPNOTSUP** if IMA is disabled and **-EINVAL** if
and => or
> + * invalid arguments are passed.
> */
> #define __BPF_FUNC_MAPPER(FN) \
> FN(unspec), \
> @@ -3970,6 +3980,7 @@ union bpf_attr {
> FN(get_current_task_btf), \
> FN(bprm_opts_set), \
> FN(ktime_get_coarse_ns), \
> + FN(ima_inode_hash), \
> /* */
>
> /* integer value in 'imm' field of BPF_CALL instruction selects which helper
> diff --git a/kernel/bpf/bpf_lsm.c b/kernel/bpf/bpf_lsm.c
> index b4f27a874092..51c36f61339e 100644
> --- a/kernel/bpf/bpf_lsm.c
> +++ b/kernel/bpf/bpf_lsm.c
> @@ -15,6 +15,7 @@
> #include <net/bpf_sk_storage.h>
> #include <linux/bpf_local_storage.h>
> #include <linux/btf_ids.h>
> +#include <linux/ima.h>
>
> /* For every LSM hook that allows attachment of BPF programs, declare a nop
> * function where a BPF program can be attached.
> @@ -75,6 +76,29 @@ const static struct bpf_func_proto bpf_bprm_opts_set_proto = {
> .arg2_type = ARG_ANYTHING,
> };
>
> +BPF_CALL_3(bpf_ima_inode_hash, struct inode *, inode, void *, dst, u32, size)
> +{
> + return ima_inode_hash(inode, dst, size);
> +}
> +
> +static bool bpf_ima_inode_hash_allowed(const struct bpf_prog *prog)
> +{
> + return bpf_lsm_is_sleepable_hook(prog->aux->attach_btf_id);
> +}
> +
> +BTF_ID_LIST_SINGLE(bpf_ima_inode_hash_btf_ids, struct, inode)
> +
> +const static struct bpf_func_proto bpf_ima_inode_hash_proto = {
> + .func = bpf_ima_inode_hash,
> + .gpl_only = false,
> + .ret_type = RET_INTEGER,
> + .arg1_type = ARG_PTR_TO_BTF_ID,
> + .arg1_btf_id = &bpf_ima_inode_hash_btf_ids[0],
> + .arg2_type = ARG_PTR_TO_UNINIT_MEM,
> + .arg3_type = ARG_CONST_SIZE_OR_ZERO,
I know ARG_CONST_SIZE_OR_ZERO provides some flexibility and may
make verifier easier to verify programs. But beyond that did
you see any real use case user will pass a zero size buf to
get hash value?
> + .allowed = bpf_ima_inode_hash_allowed,
> +};
> +
> static const struct bpf_func_proto *
> bpf_lsm_func_proto(enum bpf_func_id func_id, const struct bpf_prog *prog)
> {
> @@ -97,6 +121,8 @@ bpf_lsm_func_proto(enum bpf_func_id func_id, const struct bpf_prog *prog)
> return &bpf_task_storage_delete_proto;
> case BPF_FUNC_bprm_opts_set:
> return &bpf_bprm_opts_set_proto;
> + case BPF_FUNC_ima_inode_hash:
> + return &bpf_ima_inode_hash_proto;
> default:
> return tracing_prog_func_proto(func_id, prog);
> }
> diff --git a/scripts/bpf_helpers_doc.py b/scripts/bpf_helpers_doc.py
> index add7fcb32dcd..cb16687acb66 100755
> --- a/scripts/bpf_helpers_doc.py
> +++ b/scripts/bpf_helpers_doc.py
> @@ -430,6 +430,7 @@ class PrinterHelpers(Printer):
> 'struct tcp_request_sock',
> 'struct udp6_sock',
> 'struct task_struct',
> + 'struct inode',
>
> 'struct __sk_buff',
> 'struct sk_msg_md',
> diff --git a/tools/include/uapi/linux/bpf.h b/tools/include/uapi/linux/bpf.h
> index 3ca6146f001a..dd5b8622bb89 100644
> --- a/tools/include/uapi/linux/bpf.h
> +++ b/tools/include/uapi/linux/bpf.h
> @@ -3807,6 +3807,16 @@ union bpf_attr {
> * See: **clock_gettime**\ (**CLOCK_MONOTONIC_COARSE**)
> * Return
> * Current *ktime*.
> + *
> + * long bpf_ima_inode_hash(struct inode *inode, void *dst, u32 size)
> + * Description
> + * Returns the stored IMA hash of the *inode* (if it's avaialable).
> + * If the hash is larger than *size*, then only *size*
> + * bytes will be copied to *dst*
> + * Return
> + * The **hash_algo** of is returned on success,
of => if?
> + * **-EOPNOTSUP** if IMA is disabled and **-EINVAL** if
and => or.
> + * invalid arguments are passed.
> */
> #define __BPF_FUNC_MAPPER(FN) \
> FN(unspec), \
> @@ -3970,6 +3980,7 @@ union bpf_attr {
> FN(get_current_task_btf), \
> FN(bprm_opts_set), \
> FN(ktime_get_coarse_ns), \
> + FN(ima_inode_hash), \
> /* */
>
> /* integer value in 'imm' field of BPF_CALL instruction selects which helper
>
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