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From:   Lakshmi Ramasubramanian <nramas@linux.microsoft.com>
To:     zohar@linux.ibm.com, stephen.smalley.work@gmail.com,
        casey@schaufler-ca.com
Cc:     jmorris@namei.org, linux-integrity@vger.kernel.org,
        selinux@vger.kernel.org, linux-security-module@vger.kernel.org,
        linux-kernel@vger.kernel.org
Subject: [PATCH v2 4/5] LSM: Define SELinux function to measure security state
Date:   Thu, 16 Jul 2020 10:43:50 -0700
Message-Id: <20200716174351.20128-5-nramas@linux.microsoft.com>
In-Reply-To: <20200716174351.20128-1-nramas@linux.microsoft.com>
References: <20200716174351.20128-1-nramas@linux.microsoft.com>
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SELinux configuration and policy are some of the critical data for this
security module that needs to be measured. To enable this measurement
SELinux needs to implement the interface function,
security_measure_data(), that the LSM can call.

Define the security_state() function in SELinux to measure SELinux
configuration and policy. Call this function to measure SELinux data
when there is a change in the security module's state.

Sample measurement of SELinux state and hash of the policy:

10 e32e...5ac3 ima-buf sha256:86e8...4594 selinux-state 656e61626c65643d313b656e666f7263696e673d303b636865636b72657170726f743d313b6e6574706565723d313b6f70656e7065726d3d313b657874736f636b636c6173733d313b616c776179736e6574776f726b3d303b6367726f75707365636c6162656c3d313b6e6e706e6f737569647472616e736974696f6e3d313b67656e66737365636c6162656c73796d6c696e6b3d303b
10 f4a7...9408 ima-buf sha256:4941...68fc selinux-policy-hash 8d1d...1834

The data for selinux-state in the above measurement is:
enabled=1;enforcing=0;checkreqprot=1;network_peer_controls=1;open_perms=1;extended_socket_class=1;always_check_network=0;cgroup_seclabel=1;nnp_nosuid_transition=1;genfs_seclabel_symlinks=0;

The data for selinux-policy-hash in the above measurement is
the SHA256 hash of the SELinux policy.

Signed-off-by: Lakshmi Ramasubramanian <nramas@linux.microsoft.com>
Suggested-by: Stephen Smalley <stephen.smalley.work@gmail.com>
---
 security/selinux/Makefile           |   2 +
 security/selinux/hooks.c            |   4 +
 security/selinux/include/security.h |  26 +++++
 security/selinux/measure.c          | 158 ++++++++++++++++++++++++++++
 security/selinux/selinuxfs.c        |   1 +
 security/selinux/ss/services.c      |  66 ++++++++++--
 6 files changed, 248 insertions(+), 9 deletions(-)
 create mode 100644 security/selinux/measure.c

diff --git a/security/selinux/Makefile b/security/selinux/Makefile
index 4d8e0e8adf0b..83d512116341 100644
--- a/security/selinux/Makefile
+++ b/security/selinux/Makefile
@@ -16,6 +16,8 @@ selinux-$(CONFIG_NETLABEL) += netlabel.o
 
 selinux-$(CONFIG_SECURITY_INFINIBAND) += ibpkey.o
 
+selinux-$(CONFIG_IMA) += measure.o
+
 ccflags-y := -I$(srctree)/security/selinux -I$(srctree)/security/selinux/include
 
 $(addprefix $(obj)/,$(selinux-y)): $(obj)/flask.h
diff --git a/security/selinux/hooks.c b/security/selinux/hooks.c
index efa6108b1ce9..cda1d328339f 100644
--- a/security/selinux/hooks.c
+++ b/security/selinux/hooks.c
@@ -7259,6 +7259,8 @@ static __init int selinux_init(void)
 
 	fs_validate_description("selinux", selinux_fs_parameters);
 
+	selinux_init_measurement();
+
 	return 0;
 }
 
@@ -7284,6 +7286,7 @@ DEFINE_LSM(selinux) = {
 	.enabled = &selinux_enabled_boot,
 	.blobs = &selinux_blob_sizes,
 	.init = selinux_init,
+	.security_measure_data = selinux_measure_data,
 };
 
 #if defined(CONFIG_NETFILTER)
@@ -7394,6 +7397,7 @@ int selinux_disable(struct selinux_state *state)
 	}
 
 	selinux_mark_disabled(state);
+	selinux_measure_state(state);
 
 	pr_info("SELinux:  Disabled at runtime.\n");
 
diff --git a/security/selinux/include/security.h b/security/selinux/include/security.h
index b0e02cfe3ce1..628062ff9bba 100644
--- a/security/selinux/include/security.h
+++ b/security/selinux/include/security.h
@@ -222,16 +222,42 @@ static inline bool selinux_policycap_genfs_seclabel_symlinks(void)
 	return state->policycap[POLICYDB_CAPABILITY_GENFS_SECLABEL_SYMLINKS];
 }
 
+static inline bool selinux_checkreqprot(const struct selinux_state *state)
+{
+	return READ_ONCE(state->checkreqprot);
+}
+
 int security_mls_enabled(struct selinux_state *state);
 int security_load_policy(struct selinux_state *state,
 			 void *data, size_t len);
 int security_read_policy(struct selinux_state *state,
 			 void **data, size_t *len);
+int security_read_policy_kernel(struct selinux_state *state,
+				void **data, size_t *len);
 size_t security_policydb_len(struct selinux_state *state);
 
 int security_policycap_supported(struct selinux_state *state,
 				 unsigned int req_cap);
 
+#ifdef CONFIG_IMA
+extern void __init selinux_init_measurement(void);
+extern int selinux_measure_data(void);
+extern int selinux_measure_state(struct selinux_state *selinux_state);
+#else
+static inline void __init selinux_init_measurement(void) {}
+
+static inline int selinux_measure_data(void)
+{
+	return 0;
+}
+
+static inline int selinux_measure_state(
+	struct selinux_state *selinux_state)
+{
+	return 0;
+}
+#endif
+
 #define SEL_VEC_MAX 32
 struct av_decision {
 	u32 allowed;
diff --git a/security/selinux/measure.c b/security/selinux/measure.c
new file mode 100644
index 000000000000..27cbb309e926
--- /dev/null
+++ b/security/selinux/measure.c
@@ -0,0 +1,158 @@
+// SPDX-License-Identifier: GPL-2.0-or-later
+/*
+ * Measure SELinux state using IMA subsystem.
+ */
+#include <linux/ima.h>
+#include "security.h"
+
+/* Pre-allocated buffer used for measuring state */
+static char *selinux_state_string;
+static size_t selinux_state_string_len;
+static char *selinux_state_string_fmt =
+	"%s=%d;%s=%d;%s=%d;%s=%d;%s=%d;%s=%d;%s=%d;%s=%d;%s=%d;%s=%d;";
+
+void __init selinux_init_measurement(void)
+{
+	selinux_state_string_len =
+	snprintf(NULL, 0, selinux_state_string_fmt,
+	"enabled", 0,
+	"enforcing", 0,
+	"checkreqprot", 0,
+	selinux_policycap_names[POLICYDB_CAPABILITY_NETPEER], 0,
+	selinux_policycap_names[POLICYDB_CAPABILITY_OPENPERM], 0,
+	selinux_policycap_names[POLICYDB_CAPABILITY_EXTSOCKCLASS], 0,
+	selinux_policycap_names[POLICYDB_CAPABILITY_ALWAYSNETWORK], 0,
+	selinux_policycap_names[POLICYDB_CAPABILITY_CGROUPSECLABEL], 0,
+	selinux_policycap_names[POLICYDB_CAPABILITY_NNP_NOSUID_TRANSITION], 0,
+	selinux_policycap_names[POLICYDB_CAPABILITY_GENFS_SECLABEL_SYMLINKS],
+	0);
+
+	if (selinux_state_string_len < 0)
+		return;
+
+	++selinux_state_string_len;
+
+	selinux_state_string = kzalloc(selinux_state_string_len, GFP_KERNEL);
+	if (!selinux_state_string)
+		selinux_state_string_len = 0;
+}
+
+static int selinux_hash_policy(const char *hash_alg_name,
+			       void *policy, size_t policy_len,
+			       void **policy_hash, int *policy_hash_len)
+{
+	struct crypto_shash *tfm;
+	struct shash_desc *desc = NULL;
+	void *digest = NULL;
+	int desc_size;
+	int digest_size;
+	int ret = 0;
+
+	tfm = crypto_alloc_shash(hash_alg_name, 0, 0);
+	if (IS_ERR(tfm))
+		return PTR_ERR(tfm);
+
+	desc_size = crypto_shash_descsize(tfm) + sizeof(*desc);
+	digest_size = crypto_shash_digestsize(tfm);
+
+	digest = kmalloc(digest_size, GFP_KERNEL);
+	if (!digest) {
+		ret = -ENOMEM;
+		goto error;
+	}
+
+	desc = kzalloc(desc_size, GFP_KERNEL);
+	if (!desc) {
+		ret = -ENOMEM;
+		goto error;
+	}
+
+	desc->tfm = tfm;
+
+	ret = crypto_shash_digest(desc, policy, policy_len, digest);
+	if (ret < 0)
+		goto error;
+
+	*policy_hash_len = digest_size;
+	*policy_hash = digest;
+	digest = NULL;
+
+error:
+	kfree(desc);
+	kfree(digest);
+
+	crypto_free_shash(tfm);
+
+	if (ret)
+		pr_err("%s: error %d\n", __func__, ret);
+
+	return ret;
+}
+
+int selinux_measure_state(struct selinux_state *selinux_state)
+{
+	void *policy = NULL;
+	void *policy_hash = NULL;
+	int count;
+	size_t buflen;
+	int policy_hash_len;
+	int rc = 0;
+
+	if (!selinux_initialized(selinux_state))
+		return -EOPNOTSUPP;
+
+	if (!selinux_state_string)
+		return -ENOMEM;
+
+	count =
+	snprintf(
+	selinux_state_string, selinux_state_string_len,
+	selinux_state_string_fmt,
+	"enabled", !selinux_disabled(selinux_state),
+	"enforcing", enforcing_enabled(selinux_state),
+	"checkreqprot", selinux_checkreqprot(selinux_state),
+	selinux_policycap_names[POLICYDB_CAPABILITY_NETPEER],
+	selinux_state->policycap[POLICYDB_CAPABILITY_NETPEER],
+	selinux_policycap_names[POLICYDB_CAPABILITY_OPENPERM],
+	selinux_state->policycap[POLICYDB_CAPABILITY_OPENPERM],
+	selinux_policycap_names[POLICYDB_CAPABILITY_EXTSOCKCLASS],
+	selinux_state->policycap[POLICYDB_CAPABILITY_EXTSOCKCLASS],
+	selinux_policycap_names[POLICYDB_CAPABILITY_ALWAYSNETWORK],
+	selinux_state->policycap[POLICYDB_CAPABILITY_ALWAYSNETWORK],
+	selinux_policycap_names[POLICYDB_CAPABILITY_CGROUPSECLABEL],
+	selinux_state->policycap[POLICYDB_CAPABILITY_CGROUPSECLABEL],
+	selinux_policycap_names[POLICYDB_CAPABILITY_NNP_NOSUID_TRANSITION],
+	selinux_state->policycap[POLICYDB_CAPABILITY_NNP_NOSUID_TRANSITION],
+	selinux_policycap_names[POLICYDB_CAPABILITY_GENFS_SECLABEL_SYMLINKS],
+	selinux_state->policycap[POLICYDB_CAPABILITY_GENFS_SECLABEL_SYMLINKS]);
+
+	if (count >= 0 && count < selinux_state_string_len)
+		ima_lsm_state("selinux-state", selinux_state_string, count);
+	else {
+		pr_err("selinux state error: %d\n", count);
+		rc = -EINVAL;
+		goto out;
+	}
+
+	rc = security_read_policy_kernel(selinux_state, &policy, &buflen);
+	if (!rc)
+		rc = selinux_hash_policy("sha256", policy, buflen,
+					 &policy_hash, &policy_hash_len);
+	if (!rc)
+		ima_lsm_state("selinux-policy-hash", policy_hash,
+			      policy_hash_len);
+
+out:
+	vfree(policy);
+	kfree(policy_hash);
+
+	if (rc)
+		pr_err("%s: error %d\n", __func__, rc);
+
+	return rc;
+}
+
+int selinux_measure_data(void)
+{
+	return selinux_measure_state(&selinux_state);
+}
diff --git a/security/selinux/selinuxfs.c b/security/selinux/selinuxfs.c
index 4781314c2510..b1f70739d709 100644
--- a/security/selinux/selinuxfs.c
+++ b/security/selinux/selinuxfs.c
@@ -173,6 +173,7 @@ static ssize_t sel_write_enforce(struct file *file, const char __user *buf,
 			from_kuid(&init_user_ns, audit_get_loginuid(current)),
 			audit_get_sessionid(current));
 		enforcing_set(state, new_value);
+		selinux_measure_state(&selinux_state);
 		if (new_value)
 			avc_ss_reset(state->avc, 0);
 		selnl_notify_setenforce(new_value);
diff --git a/security/selinux/ss/services.c b/security/selinux/ss/services.c
index ef0afd878bfc..79a6b462f1fe 100644
--- a/security/selinux/ss/services.c
+++ b/security/selinux/ss/services.c
@@ -3720,14 +3720,22 @@ int security_netlbl_sid_to_secattr(struct selinux_state *state,
 }
 #endif /* CONFIG_NETLABEL */
 
+static int security_read_policy_len(struct selinux_state *state, size_t *len)
+{
+	if (!selinux_initialized(state))
+		return -EINVAL;
+
+	*len = security_policydb_len(state);
+	return 0;
+}
+
 /**
  * security_read_policy - read the policy.
  * @data: binary policy data
  * @len: length of data in bytes
- *
  */
-int security_read_policy(struct selinux_state *state,
-			 void **data, size_t *len)
+int security_read_selinux_policy(struct selinux_state *state,
+				 void **data, size_t *len)
 {
 	struct policydb *policydb = &state->ss->policydb;
 	int rc;
@@ -3736,12 +3744,6 @@ int security_read_policy(struct selinux_state *state,
 	if (!selinux_initialized(state))
 		return -EINVAL;
 
-	*len = security_policydb_len(state);
-
-	*data = vmalloc_user(*len);
-	if (!*data)
-		return -ENOMEM;
-
 	fp.data = *data;
 	fp.len = *len;
 
@@ -3754,5 +3756,51 @@ int security_read_policy(struct selinux_state *state,
 
 	*len = (unsigned long)fp.data - (unsigned long)*data;
 	return 0;
+}
+
+/**
+ * security_read_policy - read the policy.
+ * @data: binary policy data
+ * @len: length of data in bytes
+ *
+ */
+int security_read_policy(struct selinux_state *state,
+			 void **data, size_t *len)
+{
+	int rc;
+
+	rc = security_read_policy_len(state, len);
+	if (rc)
+		return rc;
+
+	*data = vmalloc_user(*len);
+	if (!*data)
+		return -ENOMEM;
+
+	return security_read_selinux_policy(state, data, len);
+}
+
+/**
+ * security_read_policy_kernel - read the policy.
+ * @data: binary policy data
+ * @len: length of data in bytes
+ *
+ * Allocates kernel memory for reading SELinux policy.
+ * This function is for internal use only and should not
+ * be used for returning data to user space
+ */
+int security_read_policy_kernel(struct selinux_state *state,
+				void **data, size_t *len)
+{
+	int rc;
+
+	rc = security_read_policy_len(state, len);
+	if (rc)
+		return rc;
+
+	*data = vmalloc(*len);
+	if (!*data)
+		return -ENOMEM;
 
+	return security_read_selinux_policy(state, data, len);
 }
-- 
2.27.0