bpf-lsm: Introduce new helper bpf_ima_file_hash()

ima_file_hash() has been modified to calculate the measurement of a file on
demand, if it has not been already performed by IMA or the measurement is
not fresh. 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>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Link: https://lore.kernel.org/bpf/20220302111404.193900-4-roberto.sassu@huawei.com

include/uapi/linux/bpf.h

@@ -5119,6 +5119,16 @@ union bpf_attr {
  *		0 on success.
  *		**-EINVAL** for invalid input
  *		**-EOPNOTSUPP** for unsupported protocol
+ *
+ * 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.
  */
 #define __BPF_FUNC_MAPPER(FN)		\
 	FN(unspec),			\
@@ -5314,6 +5324,7 @@ union bpf_attr {
 	FN(xdp_store_bytes),		\
 	FN(copy_from_user_task),	\
 	FN(skb_set_tstamp),		\
+	FN(ima_file_hash),		\
 	/* */
 
 /* integer value in 'imm' field of BPF_CALL instruction selects which helper

kernel/bpf/bpf_lsm.c

@@ -99,6 +99,24 @@ static const struct bpf_func_proto bpf_ima_inode_hash_proto = {
 	.allowed	= bpf_ima_inode_hash_allowed,
 };
 
+BPF_CALL_3(bpf_ima_file_hash, struct file *, file, void *, dst, u32, size)
+{
+	return ima_file_hash(file, dst, size);
+}
+
+BTF_ID_LIST_SINGLE(bpf_ima_file_hash_btf_ids, struct, file)
+
+static const struct bpf_func_proto bpf_ima_file_hash_proto = {
+	.func		= bpf_ima_file_hash,
+	.gpl_only	= false,
+	.ret_type	= RET_INTEGER,
+	.arg1_type	= ARG_PTR_TO_BTF_ID,
+	.arg1_btf_id	= &bpf_ima_file_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)
 {
@@ -121,6 +139,8 @@ bpf_lsm_func_proto(enum bpf_func_id func_id, const struct bpf_prog *prog)
 		return &bpf_bprm_opts_set_proto;
 	case BPF_FUNC_ima_inode_hash:
 		return prog->aux->sleepable ? &bpf_ima_inode_hash_proto : NULL;
+	case BPF_FUNC_ima_file_hash:
+		return prog->aux->sleepable ? &bpf_ima_file_hash_proto : NULL;
 	default:
 		return tracing_prog_func_proto(func_id, prog);
 	}

tools/include/uapi/linux/bpf.h

@@ -5119,6 +5119,16 @@ union bpf_attr {
  *		0 on success.
  *		**-EINVAL** for invalid input
  *		**-EOPNOTSUPP** for unsupported protocol
+ *
+ * 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.
  */
 #define __BPF_FUNC_MAPPER(FN)		\
 	FN(unspec),			\
@@ -5314,6 +5324,7 @@ union bpf_attr {
 	FN(xdp_store_bytes),		\
 	FN(copy_from_user_task),	\
 	FN(skb_set_tstamp),		\
+	FN(ima_file_hash),		\
 	/* */
 
 /* integer value in 'imm' field of BPF_CALL instruction selects which helper