Merge branch 'bpf-lsm: Extend interoperability with IMA'

Alexei Starovoitov · Alexei Starovoitov · commit a77c2cfd4ee4 · 2022-03-10T19:10:13.000-08:00
Roberto Sassu says:

====================
Extend the interoperability with IMA, to give wider flexibility for the
implementation of integrity-focused LSMs based on eBPF.

Patch 1 fixes some style issues.

Patches 2-6 give the ability to eBPF-based LSMs to take advantage of the
measurement capability of IMA without needing to setup a policy in IMA
(those LSMs might implement the policy capability themselves).

Patches 7-9 allow eBPF-based LSMs to evaluate files read by the kernel.

Changelog

v2:
- Add better description to patch 1 (suggested by Shuah)
- Recalculate digest if it is not fresh (when IMA_COLLECTED flag not set)
- Move declaration of bpf_ima_file_hash() at the end (suggested by
  Yonghong)
- Add tests to check if the digest has been recalculated
- Add deny test for bpf_kernel_read_file()
- Add description to tests

v1:
- Modify ima_file_hash() only and allow the usage of the function with the
  modified behavior by eBPF-based LSMs through the new function
  bpf_ima_file_hash() (suggested by Mimi)
- Make bpf_lsm_kernel_read_file() sleepable so that bpf_ima_inode_hash()
  and bpf_ima_file_hash() can be called inside the implementation of
  eBPF-based LSMs for this hook
====================

Signed-off-by: Alexei Starovoitov &lt;ast@kernel.org&gt;
diff --git a/include/uapi/linux/bpf.h b/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
diff --git a/kernel/bpf/bpf_lsm.c b/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);
 	}
@@ -167,6 +187,7 @@ BTF_ID(func, bpf_lsm_inode_setxattr)
 BTF_ID(func, bpf_lsm_inode_symlink)
 BTF_ID(func, bpf_lsm_inode_unlink)
 BTF_ID(func, bpf_lsm_kernel_module_request)
+BTF_ID(func, bpf_lsm_kernel_read_file)
 BTF_ID(func, bpf_lsm_kernfs_init_security)
 
 #ifdef CONFIG_KEYS
diff --git a/security/integrity/ima/ima_main.c b/security/integrity/ima/ima_main.c
@@ -418,6 +418,7 @@ int ima_file_mmap(struct file *file, unsigned long prot)
 
 /**
  * ima_file_mprotect - based on policy, limit mprotect change
+ * @vma: vm_area_struct protection is set to
  * @prot: contains the protection that will be applied by the kernel.
  *
  * Files can be mmap'ed read/write and later changed to execute to circumvent
@@ -519,20 +520,38 @@ int ima_file_check(struct file *file, int mask)
 }
 EXPORT_SYMBOL_GPL(ima_file_check);
 
-static int __ima_inode_hash(struct inode *inode, char *buf, size_t buf_size)
+static int __ima_inode_hash(struct inode *inode, struct file *file, char *buf,
+			    size_t buf_size)
 {
-	struct integrity_iint_cache *iint;
-	int hash_algo;
+	struct integrity_iint_cache *iint = NULL, tmp_iint;
+	int rc, hash_algo;
 
-	if (!ima_policy_flag)
-		return -EOPNOTSUPP;
+	if (ima_policy_flag) {
+		iint = integrity_iint_find(inode);
+		if (iint)
+			mutex_lock(&iint->mutex);
+	}
+
+	if ((!iint || !(iint->flags & IMA_COLLECTED)) && file) {
+		if (iint)
+			mutex_unlock(&iint->mutex);
+
+		memset(&tmp_iint, 0, sizeof(tmp_iint));
+		tmp_iint.inode = inode;
+		mutex_init(&tmp_iint.mutex);
+
+		rc = ima_collect_measurement(&tmp_iint, file, NULL, 0,
+					     ima_hash_algo, NULL);
+		if (rc < 0)
+			return -EOPNOTSUPP;
+
+		iint = &tmp_iint;
+		mutex_lock(&iint->mutex);
+	}
 
-	iint = integrity_iint_find(inode);
 	if (!iint)
 		return -EOPNOTSUPP;
 
-	mutex_lock(&iint->mutex);
-
 	/*
 	 * ima_file_hash can be called when ima_collect_measurement has still
 	 * not been called, we might not always have a hash.
@@ -551,12 +570,14 @@ static int __ima_inode_hash(struct inode *inode, char *buf, size_t buf_size)
 	hash_algo = iint->ima_hash->algo;
 	mutex_unlock(&iint->mutex);
 
+	if (iint == &tmp_iint)
+		kfree(iint->ima_hash);
+
 	return hash_algo;
 }
 
 /**
- * ima_file_hash - return the stored measurement if a file has been hashed and
- * is in the iint cache.
+ * ima_file_hash - return a measurement of the file
  * @file: pointer to the file
  * @buf: buffer in which to store the hash
  * @buf_size: length of the buffer
@@ -569,15 +590,15 @@ static int __ima_inode_hash(struct inode *inode, char *buf, size_t buf_size)
  * The file hash returned is based on the entire file, including the appended
  * signature.
  *
- * If IMA is disabled or if no measurement is available, return -EOPNOTSUPP.
+ * If the measurement cannot be performed, return -EOPNOTSUPP.
  * If the parameters are incorrect, return -EINVAL.
  */
 int ima_file_hash(struct file *file, char *buf, size_t buf_size)
 {
 	if (!file)
 		return -EINVAL;
 
-	return __ima_inode_hash(file_inode(file), buf, buf_size);
+	return __ima_inode_hash(file_inode(file), file, buf, buf_size);
 }
 EXPORT_SYMBOL_GPL(ima_file_hash);
 
@@ -604,14 +625,14 @@ int ima_inode_hash(struct inode *inode, char *buf, size_t buf_size)
 	if (!inode)
 		return -EINVAL;
 
-	return __ima_inode_hash(inode, buf, buf_size);
+	return __ima_inode_hash(inode, NULL, buf, buf_size);
 }
 EXPORT_SYMBOL_GPL(ima_inode_hash);
 
 /**
  * ima_post_create_tmpfile - mark newly created tmpfile as new
- * @mnt_userns:	user namespace of the mount the inode was found from
- * @file : newly created tmpfile
+ * @mnt_userns: user namespace of the mount the inode was found from
+ * @inode: inode of the newly created tmpfile
  *
  * No measuring, appraising or auditing of newly created tmpfiles is needed.
  * Skip calling process_measurement(), but indicate which newly, created
@@ -643,7 +664,7 @@ void ima_post_create_tmpfile(struct user_namespace *mnt_userns,
 
 /**
  * ima_post_path_mknod - mark as a new inode
- * @mnt_userns:	user namespace of the mount the inode was found from
+ * @mnt_userns: user namespace of the mount the inode was found from
  * @dentry: newly created dentry
  *
  * Mark files created via the mknodat syscall as new, so that the
@@ -814,8 +835,8 @@ int ima_load_data(enum kernel_load_data_id id, bool contents)
  * ima_post_load_data - appraise decision based on policy
  * @buf: pointer to in memory file contents
  * @size: size of in memory file contents
- * @id: kernel load data caller identifier
- * @description: @id-specific description of contents
+ * @load_id: kernel load data caller identifier
+ * @description: @load_id-specific description of contents
  *
  * Measure/appraise/audit in memory buffer based on policy.  Policy rules
  * are written in terms of a policy identifier.
diff --git a/tools/include/uapi/linux/bpf.h b/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
diff --git a/tools/testing/selftests/bpf/ima_setup.sh b/tools/testing/selftests/bpf/ima_setup.sh
@@ -12,7 +12,7 @@ LOG_FILE="$(mktemp /tmp/ima_setup.XXXX.log)"
 
 usage()
 {
-	echo "Usage: $0 <setup|cleanup|run> <existing_tmp_dir>"
+	echo "Usage: $0 <setup|cleanup|run|modify-bin|restore-bin|load-policy> <existing_tmp_dir>"
 	exit 1
 }
 
@@ -51,6 +51,7 @@ setup()
 
 	ensure_mount_securityfs
 	echo "measure func=BPRM_CHECK fsuuid=${mount_uuid}" > ${IMA_POLICY_FILE}
+	echo "measure func=BPRM_CHECK fsuuid=${mount_uuid}" > ${mount_dir}/policy_test
 }
 
 cleanup() {
@@ -77,6 +78,32 @@ run()
 	exec "${copied_bin_path}"
 }
 
+modify_bin()
+{
+	local tmp_dir="$1"
+	local mount_dir="${tmp_dir}/mnt"
+	local copied_bin_path="${mount_dir}/$(basename ${TEST_BINARY})"
+
+	echo "mod" >> "${copied_bin_path}"
+}
+
+restore_bin()
+{
+	local tmp_dir="$1"
+	local mount_dir="${tmp_dir}/mnt"
+	local copied_bin_path="${mount_dir}/$(basename ${TEST_BINARY})"
+
+	truncate -s -4 "${copied_bin_path}"
+}
+
+load_policy()
+{
+	local tmp_dir="$1"
+	local mount_dir="${tmp_dir}/mnt"
+
+	echo ${mount_dir}/policy_test > ${IMA_POLICY_FILE} 2> /dev/null
+}
+
 catch()
 {
 	local exit_code="$1"
@@ -105,6 +132,12 @@ main()
 		cleanup "${tmp_dir}"
 	elif [[ "${action}" == "run" ]]; then
 		run "${tmp_dir}"
+	elif [[ "${action}" == "modify-bin" ]]; then
+		modify_bin "${tmp_dir}"
+	elif [[ "${action}" == "restore-bin" ]]; then
+		restore_bin "${tmp_dir}"
+	elif [[ "${action}" == "load-policy" ]]; then
+		load_policy "${tmp_dir}"
 	else
 		echo "Unknown action: ${action}"
 		exit 1
diff --git a/tools/testing/selftests/bpf/prog_tests/test_ima.c b/tools/testing/selftests/bpf/prog_tests/test_ima.c
diff --git a/tools/testing/selftests/bpf/progs/ima.c b/tools/testing/selftests/bpf/progs/ima.c
