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authorLakshmi Ramasubramanian <nramas@linux.microsoft.com>2021-02-12 19:37:09 +0300
committerPaul Moore <paul@paul-moore.com>2021-03-09 03:39:07 +0300
commit2554a48f44370a8a73e23c58c389ae9d33effb4b (patch)
tree061d4ecaab8d87ecb7f9288f0608367ec2c57bc4 /security
parent7fa2e79a6bb924fa4b2de5766dab31f0f47b5ab6 (diff)
downloadlinux-2554a48f44370a8a73e23c58c389ae9d33effb4b.tar.xz
selinux: measure state and policy capabilities
SELinux stores the configuration state and the policy capabilities in kernel memory. Changes to this data at runtime would have an impact on the security guarantees provided by SELinux. Measuring this data through IMA subsystem provides a tamper-resistant way for an attestation service to remotely validate it at runtime. Measure the configuration state and policy capabilities by calling the IMA hook ima_measure_critical_data(). To enable SELinux data measurement, the following steps are required: 1, Add "ima_policy=critical_data" to the kernel command line arguments to enable measuring SELinux data at boot time. For example, BOOT_IMAGE=/boot/vmlinuz-5.11.0-rc3+ root=UUID=fd643309-a5d2-4ed3-b10d-3c579a5fab2f ro nomodeset security=selinux ima_policy=critical_data 2, Add the following rule to /etc/ima/ima-policy measure func=CRITICAL_DATA label=selinux Sample measurement of SELinux state and policy capabilities: 10 2122...65d8 ima-buf sha256:13c2...1292 selinux-state 696e...303b Execute the following command to extract the measured data from the IMA's runtime measurements list: grep "selinux-state" /sys/kernel/security/integrity/ima/ascii_runtime_measurements | tail -1 | cut -d' ' -f 6 | xxd -r -p The output should be a list of key-value pairs. For example, initialized=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; To verify the measurement is consistent with the current SELinux state reported on the system, compare the integer values in the following files with those set in the IMA measurement (using the following commands): - cat /sys/fs/selinux/enforce - cat /sys/fs/selinux/checkreqprot - cat /sys/fs/selinux/policy_capabilities/[capability_file] Note that the actual verification would be against an expected state and done on a separate system (likely an attestation server) requiring "initialized=1;enforcing=1;checkreqprot=0;" for a secure state and then whatever policy capabilities are actually set in the expected policy (which can be extracted from the policy itself via seinfo, for example). Signed-off-by: Lakshmi Ramasubramanian <nramas@linux.microsoft.com> Suggested-by: Stephen Smalley <stephen.smalley.work@gmail.com> Suggested-by: Paul Moore <paul@paul-moore.com> Signed-off-by: Paul Moore <paul@paul-moore.com>
Diffstat (limited to 'security')
-rw-r--r--security/selinux/ima.c87
-rw-r--r--security/selinux/include/ima.h6
-rw-r--r--security/selinux/selinuxfs.c6
-rw-r--r--security/selinux/ss/services.c2
4 files changed, 96 insertions, 5 deletions
diff --git a/security/selinux/ima.c b/security/selinux/ima.c
index 03715893ff97..34d421861bfc 100644
--- a/security/selinux/ima.c
+++ b/security/selinux/ima.c
@@ -13,18 +13,83 @@
#include "ima.h"
/*
- * selinux_ima_measure_state - Measure hash of the SELinux policy
+ * selinux_ima_collect_state - Read selinux configuration settings
*
- * @state: selinux state struct
+ * @state: selinux_state
*
- * NOTE: This function must be called with policy_mutex held.
+ * On success returns the configuration settings string.
+ * On error, returns NULL.
*/
-void selinux_ima_measure_state(struct selinux_state *state)
+static char *selinux_ima_collect_state(struct selinux_state *state)
{
+ const char *on = "=1;", *off = "=0;";
+ char *buf;
+ int buf_len, len, i, rc;
+
+ buf_len = strlen("initialized=0;enforcing=0;checkreqprot=0;") + 1;
+
+ len = strlen(on);
+ for (i = 0; i < __POLICYDB_CAPABILITY_MAX; i++)
+ buf_len += strlen(selinux_policycap_names[i]) + len;
+
+ buf = kzalloc(buf_len, GFP_KERNEL);
+ if (!buf)
+ return NULL;
+
+ rc = strscpy(buf, "initialized", buf_len);
+ WARN_ON(rc < 0);
+
+ rc = strlcat(buf, selinux_initialized(state) ? on : off, buf_len);
+ WARN_ON(rc >= buf_len);
+
+ rc = strlcat(buf, "enforcing", buf_len);
+ WARN_ON(rc >= buf_len);
+
+ rc = strlcat(buf, enforcing_enabled(state) ? on : off, buf_len);
+ WARN_ON(rc >= buf_len);
+
+ rc = strlcat(buf, "checkreqprot", buf_len);
+ WARN_ON(rc >= buf_len);
+
+ rc = strlcat(buf, checkreqprot_get(state) ? on : off, buf_len);
+ WARN_ON(rc >= buf_len);
+
+ for (i = 0; i < __POLICYDB_CAPABILITY_MAX; i++) {
+ rc = strlcat(buf, selinux_policycap_names[i], buf_len);
+ WARN_ON(rc >= buf_len);
+
+ rc = strlcat(buf, state->policycap[i] ? on : off, buf_len);
+ WARN_ON(rc >= buf_len);
+ }
+
+ return buf;
+}
+
+/*
+ * selinux_ima_measure_state_locked - Measure SELinux state and hash of policy
+ *
+ * @state: selinux state struct
+ */
+void selinux_ima_measure_state_locked(struct selinux_state *state)
+{
+ char *state_str = NULL;
void *policy = NULL;
size_t policy_len;
int rc = 0;
+ WARN_ON(!mutex_is_locked(&state->policy_mutex));
+
+ state_str = selinux_ima_collect_state(state);
+ if (!state_str) {
+ pr_err("SELinux: %s: failed to read state.\n", __func__);
+ return;
+ }
+
+ ima_measure_critical_data("selinux", "selinux-state",
+ state_str, strlen(state_str), false);
+
+ kfree(state_str);
+
/*
* Measure SELinux policy only after initialization is completed.
*/
@@ -42,3 +107,17 @@ void selinux_ima_measure_state(struct selinux_state *state)
vfree(policy);
}
+
+/*
+ * selinux_ima_measure_state - Measure SELinux state and hash of policy
+ *
+ * @state: selinux state struct
+ */
+void selinux_ima_measure_state(struct selinux_state *state)
+{
+ WARN_ON(mutex_is_locked(&state->policy_mutex));
+
+ mutex_lock(&state->policy_mutex);
+ selinux_ima_measure_state_locked(state);
+ mutex_unlock(&state->policy_mutex);
+}
diff --git a/security/selinux/include/ima.h b/security/selinux/include/ima.h
index d69c36611423..75ca92b4a462 100644
--- a/security/selinux/include/ima.h
+++ b/security/selinux/include/ima.h
@@ -15,10 +15,16 @@
#ifdef CONFIG_IMA
extern void selinux_ima_measure_state(struct selinux_state *selinux_state);
+extern void selinux_ima_measure_state_locked(
+ struct selinux_state *selinux_state);
#else
static inline void selinux_ima_measure_state(struct selinux_state *selinux_state)
{
}
+static inline void selinux_ima_measure_state_locked(
+ struct selinux_state *selinux_state)
+{
+}
#endif
#endif /* _SELINUX_IMA_H_ */
diff --git a/security/selinux/selinuxfs.c b/security/selinux/selinuxfs.c
index 01a7d50ed39b..dc9d7674f592 100644
--- a/security/selinux/selinuxfs.c
+++ b/security/selinux/selinuxfs.c
@@ -41,6 +41,7 @@
#include "security.h"
#include "objsec.h"
#include "conditional.h"
+#include "ima.h"
enum sel_inos {
SEL_ROOT_INO = 2,
@@ -182,6 +183,8 @@ static ssize_t sel_write_enforce(struct file *file, const char __user *buf,
selinux_status_update_setenforce(state, new_value);
if (!new_value)
call_blocking_lsm_notifier(LSM_POLICY_CHANGE, NULL);
+
+ selinux_ima_measure_state(state);
}
length = count;
out:
@@ -762,6 +765,9 @@ static ssize_t sel_write_checkreqprot(struct file *file, const char __user *buf,
checkreqprot_set(fsi->state, (new_value ? 1 : 0));
length = count;
+
+ selinux_ima_measure_state(fsi->state);
+
out:
kfree(page);
return length;
diff --git a/security/selinux/ss/services.c b/security/selinux/ss/services.c
index 3438d0130378..f37375c9553f 100644
--- a/security/selinux/ss/services.c
+++ b/security/selinux/ss/services.c
@@ -2179,7 +2179,7 @@ static void selinux_notify_policy_change(struct selinux_state *state,
selinux_status_update_policyload(state, seqno);
selinux_netlbl_cache_invalidate();
selinux_xfrm_notify_policyload();
- selinux_ima_measure_state(state);
+ selinux_ima_measure_state_locked(state);
}
void selinux_policy_commit(struct selinux_state *state,