Commit 27672f0d authored by KP Singh's avatar KP Singh Committed by Daniel Borkmann
Browse files

bpf: Add a BPF helper for getting the IMA hash of an inode 



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: default avatarKP Singh <kpsingh@google.com>
Signed-off-by: default avatarDaniel Borkmann <daniel@iogearbox.net>
Acked-by: default avatarYonghong Song <yhs@fb.com>
Link: https://lore.kernel.org/bpf/20201124151210.1081188-3-kpsingh@chromium.org
parent 403319be

include/uapi/linux/bpf.h

+11 −0
Original line number Diff line number Diff line
@@ -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** is returned on success,

 *		**-EOPNOTSUP** if IMA is disabled or **-EINVAL** if

 *		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

kernel/bpf/bpf_lsm.c

+26 −0
Original line number Diff line number Diff line
@@ -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,

	.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 prog->aux->sleepable ? &bpf_ima_inode_hash_proto : NULL;

	default:

		return tracing_prog_func_proto(func_id, prog);

	}

scripts/bpf_helpers_doc.py

+2 −0
Original line number Diff line number Diff line
@@ -436,6 +436,7 @@ class PrinterHelpers(Printer): 
            'struct xdp_md',

            'struct path',

            'struct btf_ptr',

            'struct inode',

    ]

    known_types = {

            '...',
@@ -480,6 +481,7 @@ class PrinterHelpers(Printer): 
            'struct task_struct',

            'struct path',

            'struct btf_ptr',

            'struct inode',

    }

    mapped_types = {

            'u8': '__u8',

tools/include/uapi/linux/bpf.h

+11 −0
Original line number Diff line number Diff line
@@ -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** is returned on success,

 *		**-EOPNOTSUP** if IMA is disabled or **-EINVAL** if

 *		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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