[PATCH 4/5] LSM: Define SELinux function to measure security state

Lakshmi Ramasubramanian
2020-06-13T02:41:54Z

SELinux needs to implement the interface function, security_state(), for
the LSM to gather SELinux data for measuring. Define the security_state()
function in SELinux.

The security modules should be able to notify the LSM when there is
a change in the module's data. Define a function namely
security_state_change() in the LSM that the security modules
can call to provide the updated data for measurement.

Call security_state_change() function from SELinux to report data
when SELinux's state is updated.

Signed-off-by: Lakshmi Ramasubramanian <nramas@linux.microsoft.com>
---
include/linux/lsm_hooks.h | 3 ++
security/security.c | 5 ++++
security/selinux/hooks.c | 43 +++++++++++++++++++++++++++++
security/selinux/include/security.h | 2 ++
security/selinux/selinuxfs.c | 1 +
5 files changed, 54 insertions(+)

diff --git a/include/linux/lsm_hooks.h b/include/linux/lsm_hooks.h
index da248c3fd4ac..a63de046139e 100644
--- a/include/linux/lsm_hooks.h
+++ b/include/linux/lsm_hooks.h
@@ -1572,6 +1572,9 @@ struct lsm_info {
int *state_len); /*Optional */
};

+/* Called by LSMs to notify security state change */
+extern void security_state_change(char *lsm_name, void *state, int state_len);
+
extern struct lsm_info __start_lsm_info[], __end_lsm_info[];
extern struct lsm_info __start_early_lsm_info[], __end_early_lsm_info[];

diff --git a/security/security.c b/security/security.c
index a6e2d1cd95af..e7175db5a093 100644
--- a/security/security.c
+++ b/security/security.c
@@ -238,6 +238,11 @@ static void __init initialize_lsm(struct lsm_info *lsm)
}
}

+void security_state_change(char *lsm_name, void *state, int state_len)
+{
+ ima_lsm_state(lsm_name, state, state_len);
+}
+
static int measure_security_state(struct lsm_info *lsm)
{
char *lsm_name = NULL;
diff --git a/security/selinux/hooks.c b/security/selinux/hooks.c
index 7e954b555be6..bbc908a1fcd1 100644
--- a/security/selinux/hooks.c
+++ b/security/selinux/hooks.c
@@ -7225,6 +7225,47 @@ static __init int selinux_init(void)
return 0;
}

+static int selinux_security_state(char **lsm_name, void **state,
+ int *state_len)
+{
+ int rc = 0;
+ char *new_state;
+ static char *security_state_string = "enabled=%d;enforcing=%d";
+
+ *lsm_name = kstrdup("selinux", GFP_KERNEL);
+ if (!*lsm_name)
+ return -ENOMEM;
+
+ new_state = kzalloc(strlen(security_state_string) + 1, GFP_KERNEL);
+ if (!new_state) {
+ kfree(*lsm_name);
+ *lsm_name = NULL;
+ rc = -ENOMEM;
+ goto out;
+ }
+
+ *state_len = sprintf(new_state, security_state_string,
+ !selinux_disabled(&selinux_state),
+ enforcing_enabled(&selinux_state));
+ *state = new_state;
+
+out:
+ return rc;
+}
+
+void notify_security_state_change(void)
+{
+ char *lsm_name = NULL;
+ void *state = NULL;
+ int state_len = 0;
+
+ if (!selinux_security_state(&lsm_name, &state, &state_len)) {
+ security_state_change(lsm_name, state, state_len);
+ kfree(state);
+ kfree(lsm_name);
+ }
+}
+
static void delayed_superblock_init(struct super_block *sb, void *unused)
{
selinux_set_mnt_opts(sb, NULL, 0, NULL);
@@ -7247,6 +7288,7 @@ DEFINE_LSM(selinux) = {
.enabled = &selinux_enabled_boot,
.blobs = &selinux_blob_sizes,
.init = selinux_init,
+ .security_state = selinux_security_state,
};

#if defined(CONFIG_NETFILTER)
@@ -7357,6 +7399,7 @@ int selinux_disable(struct selinux_state *state)
}

selinux_mark_disabled(state);
+ notify_security_state_change();

pr_info("SELinux: Disabled at runtime.\n");

diff --git a/security/selinux/include/security.h b/security/selinux/include/security.h
index b0e02cfe3ce1..83c6ada45c7c 100644
--- a/security/selinux/include/security.h
+++ b/security/selinux/include/security.h
@@ -232,6 +232,8 @@ size_t security_policydb_len(struct selinux_state *state);
int security_policycap_supported(struct selinux_state *state,
unsigned int req_cap);

+void notify_security_state_change(void);
+
#define SEL_VEC_MAX 32
struct av_decision {
u32 allowed;
diff --git a/security/selinux/selinuxfs.c b/security/selinux/selinuxfs.c
index 4781314c2510..8a5ba32a7775 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);
+ notify_security_state_change();
if (new_value)
avc_ss_reset(state->avc, 0);
selnl_notify_setenforce(new_value);
--
2.27.0