Critical data structures of security modules are currently not measured.
Therefore an attestation service, for instance, would not be able to
attest whether the security modules are always operating with the policies
and configuration that the system administrator had setup. The policies
and configuration for the security modules could be tampered with by
malware by exploiting Kernel vulnerabilities or modified through some
inadvertent actions on the system. Measuring such critical data would
enable an attestation service to better assess the state of the system.
IMA subsystem measures system files, command line arguments passed to
kexec, boot aggregate, keys, etc. It can be used to measure critical
data structures of security modules as well.
This change aims to address measuring critical data structures
of security modules when they are initialized, when they are updated
at runtime, and also periodically to detect any tampering.
This change set is based off of Linux Kernel version 5.8-rc5.
The following patch needs to be applied first before applying
the patches in this patch set:
https://patchwork.kernel.org/patch/11612989/
Change log:
v2:
=> Pass selinux_state struct as parameter to the function
that measures SELinux data.
=> Use strings from selinux_policycap_names array for SELinux
state measurement.
=> Refactored security_read_policy() to alloc kernel or user
virtual memory and then read the SELinux policy.
v1:
=> Per Stephen Smalley's suggestion added selinux_state booleans
and hash of SELinux policy in the measured data for SELinux.
=> Call IMA hook from the security module directly instead of
redirecting through the LSM.
Lakshmi Ramasubramanian (5):
IMA: Add LSM_STATE func to measure LSM data
IMA: Define an IMA hook to measure LSM data
LSM: Add security_measure_data in lsm_info struct
LSM: Define SELinux function to measure security state
LSM: Define workqueue for measuring security module state
Documentation/ABI/testing/ima_policy | 6 +-
include/linux/ima.h | 4 +
include/linux/lsm_hooks.h | 3 +
security/integrity/ima/ima.h | 1 +
security/integrity/ima/ima_api.c | 2 +-
security/integrity/ima/ima_main.c | 17 +++
security/integrity/ima/ima_policy.c | 29 ++++-
security/security.c | 74 ++++++++++++-
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 +++++++++--
14 files changed, 376 insertions(+), 17 deletions(-)
create mode 100644 security/selinux/measure.c
--
2.27.0
Critical data structures of security modules need to be measured to
enable an attestation service to verify if the policies and
configuration have been setup correctly and that they haven't been
tampered with at runtime. A new IMA policy is required for handling
this measurement.
Define a new IMA policy func namely LSM_STATE to measure data provided
by security modules. Update ima_match_rules() to check for LSM_STATE
and ima_parse_rule() to handle LSM_STATE.
Signed-off-by: Lakshmi Ramasubramanian <[email protected]>
---
Documentation/ABI/testing/ima_policy | 6 +++++-
security/integrity/ima/ima.h | 1 +
security/integrity/ima/ima_api.c | 2 +-
security/integrity/ima/ima_policy.c | 29 +++++++++++++++++++++++-----
4 files changed, 31 insertions(+), 7 deletions(-)
diff --git a/Documentation/ABI/testing/ima_policy b/Documentation/ABI/testing/ima_policy
index cd572912c593..355bc3eade33 100644
--- a/Documentation/ABI/testing/ima_policy
+++ b/Documentation/ABI/testing/ima_policy
@@ -29,7 +29,7 @@ Description:
base: func:= [BPRM_CHECK][MMAP_CHECK][CREDS_CHECK][FILE_CHECK][MODULE_CHECK]
[FIRMWARE_CHECK]
[KEXEC_KERNEL_CHECK] [KEXEC_INITRAMFS_CHECK]
- [KEXEC_CMDLINE] [KEY_CHECK]
+ [KEXEC_CMDLINE] [KEY_CHECK] [LSM_STATE]
mask:= [[^]MAY_READ] [[^]MAY_WRITE] [[^]MAY_APPEND]
[[^]MAY_EXEC]
fsmagic:= hex value
@@ -125,3 +125,7 @@ Description:
keys added to .builtin_trusted_keys or .ima keyring:
measure func=KEY_CHECK keyrings=.builtin_trusted_keys|.ima
+
+ Example of measure rule using LSM_STATE to measure LSM data:
+
+ measure func=LSM_STATE
diff --git a/security/integrity/ima/ima.h b/security/integrity/ima/ima.h
index 4515975cc540..880fda11a61b 100644
--- a/security/integrity/ima/ima.h
+++ b/security/integrity/ima/ima.h
@@ -200,6 +200,7 @@ static inline unsigned int ima_hash_key(u8 *digest)
hook(POLICY_CHECK, policy) \
hook(KEXEC_CMDLINE, kexec_cmdline) \
hook(KEY_CHECK, key) \
+ hook(LSM_STATE, lsm_state) \
hook(MAX_CHECK, none)
#define __ima_hook_enumify(ENUM, str) ENUM,
diff --git a/security/integrity/ima/ima_api.c b/security/integrity/ima/ima_api.c
index bf22de8b7ce0..0cebd2404dcf 100644
--- a/security/integrity/ima/ima_api.c
+++ b/security/integrity/ima/ima_api.c
@@ -176,7 +176,7 @@ void ima_add_violation(struct file *file, const unsigned char *filename,
* subj=, obj=, type=, func=, mask=, fsmagic=
* subj,obj, and type: are LSM specific.
* func: FILE_CHECK | BPRM_CHECK | CREDS_CHECK | MMAP_CHECK | MODULE_CHECK
- * | KEXEC_CMDLINE | KEY_CHECK
+ * | KEXEC_CMDLINE | KEY_CHECK | LSM_STATE
* mask: contains the permission mask
* fsmagic: hex value
*
diff --git a/security/integrity/ima/ima_policy.c b/security/integrity/ima/ima_policy.c
index 66aa3e17a888..fc8457d9242b 100644
--- a/security/integrity/ima/ima_policy.c
+++ b/security/integrity/ima/ima_policy.c
@@ -417,15 +417,31 @@ static bool ima_match_rules(struct ima_rule_entry *rule, struct inode *inode,
const char *keyring)
{
int i;
+ int funcmatch = 0;
- if ((func == KEXEC_CMDLINE) || (func == KEY_CHECK)) {
+ switch (func) {
+ case KEXEC_CMDLINE:
+ case KEY_CHECK:
+ case LSM_STATE:
if ((rule->flags & IMA_FUNC) && (rule->func == func)) {
if (func == KEY_CHECK)
- return ima_match_keyring(rule, keyring, cred);
- return true;
- }
- return false;
+ funcmatch = ima_match_keyring(rule, keyring,
+ cred) ? 1 : -1;
+ else
+ funcmatch = 1;
+ } else
+ funcmatch = -1;
+
+ break;
+
+ default:
+ funcmatch = 0;
+ break;
}
+
+ if (funcmatch)
+ return (funcmatch == 1) ? true : false;
+
if ((rule->flags & IMA_FUNC) &&
(rule->func != func && func != POST_SETATTR))
return false;
@@ -1068,6 +1084,9 @@ static int ima_parse_rule(char *rule, struct ima_rule_entry *entry)
entry->func = KEXEC_CMDLINE;
else if (strcmp(args[0].from, "KEY_CHECK") == 0)
entry->func = KEY_CHECK;
+ else if (strcmp(args[0].from, "LSM_STATE") == 0)
+ entry->func = LSM_STATE;
+
else
result = -EINVAL;
if (!result)
--
2.27.0
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 <[email protected]>
Suggested-by: Stephen Smalley <[email protected]>
---
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
The security modules that require their data to be measured using
the IMA subsystem need to define a function that the LSM can call
to trigger the measurement.
Add a function pointer field namely security_measure_data in lsm_info
structure. Update LSM to call this security module function, if defined,
to measure the security module's data using the IMA subsystem.
Signed-off-by: Lakshmi Ramasubramanian <[email protected]>
---
include/linux/lsm_hooks.h | 3 +++
security/security.c | 48 ++++++++++++++++++++++++++++++++++++++-
2 files changed, 50 insertions(+), 1 deletion(-)
diff --git a/include/linux/lsm_hooks.h b/include/linux/lsm_hooks.h
index 95b7c1d32062..56f0e524838c 100644
--- a/include/linux/lsm_hooks.h
+++ b/include/linux/lsm_hooks.h
@@ -1591,6 +1591,9 @@ struct lsm_info {
int *enabled; /* Optional: controlled by CONFIG_LSM */
int (*init)(void); /* Required. */
struct lsm_blob_sizes *blobs; /* Optional: for blob sharing. */
+ int (*security_measure_data)(void); /* Optional: for measuring
+ * security module data.
+ */
};
extern struct lsm_info __start_lsm_info[], __end_lsm_info[];
diff --git a/security/security.c b/security/security.c
index 70a7ad357bc6..1afa2aebc3ac 100644
--- a/security/security.c
+++ b/security/security.c
@@ -86,6 +86,9 @@ static __initconst const char * const builtin_lsm_order = CONFIG_LSM;
static __initdata struct lsm_info **ordered_lsms;
static __initdata struct lsm_info *exclusive;
+static struct lsm_info *security_state_lsms;
+static int security_state_lsms_count;
+
static __initdata bool debug;
#define init_debug(...) \
do { \
@@ -235,6 +238,45 @@ static void __init initialize_lsm(struct lsm_info *lsm)
}
}
+static int measure_security_state(struct lsm_info *lsm)
+{
+ if (!lsm->security_measure_data)
+ return 0;
+
+ return lsm->security_measure_data();
+}
+
+static void __init initialize_security_state_lsms(void)
+{
+ struct lsm_info **lsm;
+ int count = 0;
+ int inx;
+
+ for (lsm = ordered_lsms; *lsm; lsm++) {
+ if ((*lsm)->security_measure_data)
+ count++;
+ }
+
+ if (count == 0)
+ return;
+
+ security_state_lsms = kcalloc(count, sizeof(struct lsm_info),
+ GFP_KERNEL);
+ if (!security_state_lsms)
+ return;
+
+ inx = 0;
+ for (lsm = ordered_lsms; *lsm; lsm++) {
+ if ((*lsm)->security_measure_data) {
+ security_state_lsms[inx].security_measure_data =
+ (*lsm)->security_measure_data;
+ inx++;
+ }
+ }
+
+ security_state_lsms_count = count;
+}
+
/* Populate ordered LSMs list from comma-separated LSM name list. */
static void __init ordered_lsm_parse(const char *order, const char *origin)
{
@@ -352,8 +394,12 @@ static void __init ordered_lsm_init(void)
lsm_early_cred((struct cred *) current->cred);
lsm_early_task(current);
- for (lsm = ordered_lsms; *lsm; lsm++)
+ for (lsm = ordered_lsms; *lsm; lsm++) {
initialize_lsm(*lsm);
+ measure_security_state(*lsm);
+ }
+
+ initialize_security_state_lsms();
kfree(ordered_lsms);
}
--
2.27.0
Data structures critical to the functioning of a security module could
be tampered with by malware or changed inadvertently at runtime
thereby disabling or reducing the security guarantees provided by
the security module. Such critical data need to be periodically checked
and measured, if there is any change. This would enable an attestation
service, for instance, to verify that the security modules are operating
with the configuration and policy setup by the system administrator.
Define a workqueue in the LSM and invoke the security modules in
the workqueue handler to check their data and measure.
Note that the data given by the security module would be measured by
the IMA subsystem only if it has changed since the last time it was
measured.
Signed-off-by: Lakshmi Ramasubramanian <[email protected]>
---
security/security.c | 26 ++++++++++++++++++++++++++
1 file changed, 26 insertions(+)
diff --git a/security/security.c b/security/security.c
index 1afa2aebc3ac..63b30da337d8 100644
--- a/security/security.c
+++ b/security/security.c
@@ -89,6 +89,11 @@ static __initdata struct lsm_info *exclusive;
static struct lsm_info *security_state_lsms;
static int security_state_lsms_count;
+static long security_state_timeout = 300000; /* 5 Minutes */
+static void security_state_handler(struct work_struct *work);
+static DECLARE_DELAYED_WORK(security_state_delayed_work,
+ security_state_handler);
+
static __initdata bool debug;
#define init_debug(...) \
do { \
@@ -277,6 +282,26 @@ static void __init initialize_security_state_lsms(void)
security_state_lsms_count = count;
}
+static void initialize_security_state_monitor(void)
+{
+ if (security_state_lsms_count == 0)
+ return;
+
+ schedule_delayed_work(&security_state_delayed_work,
+ msecs_to_jiffies(security_state_timeout));
+}
+
+static void security_state_handler(struct work_struct *work)
+{
+ int inx;
+
+ for (inx = 0; inx < security_state_lsms_count; inx++)
+ measure_security_state(&(security_state_lsms[inx]));
+
+ schedule_delayed_work(&security_state_delayed_work,
+ msecs_to_jiffies(security_state_timeout));
+}
+
/* Populate ordered LSMs list from comma-separated LSM name list. */
static void __init ordered_lsm_parse(const char *order, const char *origin)
{
@@ -400,6 +425,7 @@ static void __init ordered_lsm_init(void)
}
initialize_security_state_lsms();
+ initialize_security_state_monitor();
kfree(ordered_lsms);
}
--
2.27.0
IMA subsystem needs to define an IMA hook that the security modules can
call to measure critical data of the security modules.
Define a new IMA hook, namely ima_lsm_state(), that the security modules
can call to measure data.
Signed-off-by: Lakshmi Ramasubramanian <[email protected]>
---
include/linux/ima.h | 4 ++++
security/integrity/ima/ima_main.c | 17 +++++++++++++++++
2 files changed, 21 insertions(+)
diff --git a/include/linux/ima.h b/include/linux/ima.h
index 9164e1534ec9..7e2686f4953a 100644
--- a/include/linux/ima.h
+++ b/include/linux/ima.h
@@ -26,6 +26,7 @@ extern int ima_post_read_file(struct file *file, void *buf, loff_t size,
extern void ima_post_path_mknod(struct dentry *dentry);
extern int ima_file_hash(struct file *file, char *buf, size_t buf_size);
extern void ima_kexec_cmdline(const void *buf, int size);
+extern void ima_lsm_state(const char *lsm_event_name, const void *buf, int size);
#ifdef CONFIG_IMA_KEXEC
extern void ima_add_kexec_buffer(struct kimage *image);
@@ -104,6 +105,9 @@ static inline int ima_file_hash(struct file *file, char *buf, size_t buf_size)
}
static inline void ima_kexec_cmdline(const void *buf, int size) {}
+
+static inline void ima_lsm_state(const char *lsm_event_name,
+ const void *buf, int size) {}
#endif /* CONFIG_IMA */
#ifndef CONFIG_IMA_KEXEC
diff --git a/security/integrity/ima/ima_main.c b/security/integrity/ima/ima_main.c
index 8351b2fd48e0..04d9a1d35300 100644
--- a/security/integrity/ima/ima_main.c
+++ b/security/integrity/ima/ima_main.c
@@ -835,6 +835,23 @@ void ima_kexec_cmdline(const void *buf, int size)
KEXEC_CMDLINE, 0, NULL);
}
+/**
+ * ima_lsm_state - measure LSM specific state
+ * @lsm_event_name: LSM event
+ * @buf: pointer to buffer containing LSM specific state
+ * @size: Number of bytes in buf
+ *
+ * Buffers can only be measured, not appraised.
+ */
+void ima_lsm_state(const char *lsm_event_name, const void *buf, int size)
+{
+ if (!lsm_event_name || !buf || !size)
+ return;
+
+ process_buffer_measurement(buf, size, lsm_event_name,
+ LSM_STATE, 0, NULL);
+}
+
static int __init init_ima(void)
{
int error;
--
2.27.0
On Thu, Jul 16, 2020 at 1:44 PM Lakshmi Ramasubramanian
<[email protected]> wrote:
>
> 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.
Can you show an example of how to verify that the above measurement
matches a given state and policy, e.g. the sha256sum commands and
inputs to reproduce the same from an expected state and policy?
>
> Signed-off-by: Lakshmi Ramasubramanian <[email protected]>
> Suggested-by: Stephen Smalley <[email protected]>
> ---
> 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);
I was thinking you'd dynamically construct the format string with a
for loop from 0 to POLICYDB_CAPABILITY_MAX
and likewise for the values so that we wouldn't have to patch this
code every time we add a new one.
> +
> + if (selinux_state_string_len < 0)
> + return;
How can this happen legitimately (i.e. as a result of something other
than a kernel bug)?
> +
> + ++selinux_state_string_len;
> +
> + selinux_state_string = kzalloc(selinux_state_string_len, GFP_KERNEL);
> + if (!selinux_state_string)
> + selinux_state_string_len = 0;
> +}
Not sure about this error handling approach (silent, proceeding as if
the length was zero and then later failing with ENOMEM on every
attempt?). I'd be more inclined to panic/BUG here but I know Linus
doesn't like that.
> + if (ret)
> + pr_err("%s: error %d\n", __func__, ret);
This doesn't seem terribly useful as an error message; I'd be inclined
to drop it.
On 7/16/20 11:54 AM, Stephen Smalley wrote:
>> 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.
>
> Can you show an example of how to verify that the above measurement
> matches a given state and policy, e.g. the sha256sum commands and
> inputs to reproduce the same from an expected state and policy?
Sure - I'll provide an example.
>> +/* 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);
>
> I was thinking you'd dynamically construct the format string with a
> for loop from 0 to POLICYDB_CAPABILITY_MAX
> and likewise for the values so that we wouldn't have to patch this
> code every time we add a new one.
That's a good point - will do.
>
>> +
>> + if (selinux_state_string_len < 0)
>> + return;
>
> How can this happen legitimately (i.e. as a result of something other
> than a kernel bug)?
Since snprintf can return an error I wanted to handle that. But I agree
this should not happen for the input data to snprintf used here.
>
>> +
>> + ++selinux_state_string_len;
>> +
>> + selinux_state_string = kzalloc(selinux_state_string_len, GFP_KERNEL);
>> + if (!selinux_state_string)
>> + selinux_state_string_len = 0;
>> +}
>
> Not sure about this error handling approach (silent, proceeding as if
> the length was zero and then later failing with ENOMEM on every
> attempt?). I'd be more inclined to panic/BUG here but I know Linus
> doesn't like that.
I am not sure if failing (kernel panic/BUG) to "measure" LSM data under
memory pressure conditions is the right thing. But I am open to treating
this error as a fatal error. Please let me know.
>
>> + if (ret)
>> + pr_err("%s: error %d\n", __func__, ret);
>
> This doesn't seem terribly useful as an error message; I'd be inclined
> to drop it.
>
Will do.
thanks,
-lakshmi
On Thu, Jul 16, 2020 at 3:13 PM Lakshmi Ramasubramanian
<[email protected]> wrote:
>
> On 7/16/20 11:54 AM, Stephen Smalley wrote:
> > Not sure about this error handling approach (silent, proceeding as if
> > the length was zero and then later failing with ENOMEM on every
> > attempt?). I'd be more inclined to panic/BUG here but I know Linus
> > doesn't like that.
> I am not sure if failing (kernel panic/BUG) to "measure" LSM data under
> memory pressure conditions is the right thing. But I am open to treating
> this error as a fatal error. Please let me know.
Let's at least log an error message since it otherwise silently
disables all measuring of security state.
Also not sure why we bother returning errors from
selinux_measure_data() since nothing appears to check or use the
result.
Don't know if integrity/IMA has any equivalent to the audit
subsystem's concept of audit_failure settings to control whether
errors that prevent auditing (measuring) are handled silently, with a
log message, or via a panic. If not, I guess that can be explored
separately.
On 7/16/20 12:45 PM, Stephen Smalley wrote:
> On Thu, Jul 16, 2020 at 3:13 PM Lakshmi Ramasubramanian
> <[email protected]> wrote:
>>
>> On 7/16/20 11:54 AM, Stephen Smalley wrote:
>>> Not sure about this error handling approach (silent, proceeding as if
>>> the length was zero and then later failing with ENOMEM on every
>>> attempt?). I'd be more inclined to panic/BUG here but I know Linus
>>> doesn't like that.
>> I am not sure if failing (kernel panic/BUG) to "measure" LSM data under
>> memory pressure conditions is the right thing. But I am open to treating
>> this error as a fatal error. Please let me know.
>
> Let's at least log an error message since it otherwise silently
> disables all measuring of security state.
Agree - will log error messages as appropriate.
> Also not sure why we bother returning errors from
> selinux_measure_data() since nothing appears to check or use the
> result.
Maybe SELinux can log audit messages on failures, but I guess it may be
better to do that closer to where the error occurs.
Will change selinux_measure_data() to void function.
> Don't know if integrity/IMA has any equivalent to the audit
> subsystem's concept of audit_failure settings to control whether
> errors that prevent auditing (measuring) are handled silently, with a
> log message, or via a panic. If not, I guess that can be explored
> separately.
>
Yes - integrity subsystem logs audit messages for errors\failures.
-lakshmi