diff mbox series

[v1,4/5] LSM: Define SELinux function to measure security state

Message ID 20200715154853.23374-5-nramas@linux.microsoft.com
State New
Headers show
Series LSM: Measure security module state | expand

Commit Message

Lakshmi Ramasubramanian July 15, 2020, 3:48 p.m. UTC
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_state(), 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;netpeer=1;openperm=1;extsockclass=1;alwaysnetwork=0;cgroupseclabel=1;nnpnosuidtransition=1;genfsseclabelsymlink=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            |   2 +
 security/selinux/include/security.h |  19 +++++
 security/selinux/measure.c          | 122 ++++++++++++++++++++++++++++
 security/selinux/selinuxfs.c        |   1 +
 security/selinux/ss/services.c      |  23 +++++-
 6 files changed, 165 insertions(+), 4 deletions(-)
 create mode 100644 security/selinux/measure.c

Comments

Stephen Smalley July 15, 2020, 6:04 p.m. UTC | #1
On Wed, Jul 15, 2020 at 11:48 AM Lakshmi Ramasubramanian
<nramas@linux.microsoft.com> 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_state(), 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;netpeer=1;openperm=1;extsockclass=1;alwaysnetwork=0;cgroupseclabel=1;nnpnosuidtransition=1;genfsseclabelsymlink=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>
> ---

> diff --git a/security/selinux/include/security.h b/security/selinux/include/security.h
> index b0e02cfe3ce1..691c7e35f82a 100644
> --- a/security/selinux/include/security.h
> +++ b/security/selinux/include/security.h
> @@ -222,16 +222,35 @@ static inline bool selinux_policycap_genfs_seclabel_symlinks(void)
>         return state->policycap[POLICYDB_CAPABILITY_GENFS_SECLABEL_SYMLINKS];
>  }
>
> +static inline bool selinux_checkreqprot(void)
> +{
> +       struct selinux_state *state = &selinux_state;
> +
> +       return state->checkreqprot;
> +}

Probably should use READ_ONCE().

> diff --git a/security/selinux/measure.c b/security/selinux/measure.c
> new file mode 100644
> index 000000000000..b909e8e61542
> --- /dev/null
> +++ b/security/selinux/measure.c
> @@ -0,0 +1,122 @@
> +int selinux_security_state(void)

Let's call this selinux_measure_state() or similar.  Needs a verb. And
pass it a struct selinux_state * pointer argument to be measured, even
though initially it will always be passed &selinux_state.  The
encapsulation of selinux state within selinux_state was to support
multiple selinux namespaces in the future, each with their own state.

> +{
> +       int rc = 0;
> +       int count;
> +       size_t buflen;
> +       int policy_hash_len;
> +       char *state = NULL;
> +       void *policy = NULL;
> +       void *policy_hash = NULL;
> +       static char *security_state_string =
> +                       "enabled=%d;enforcing=%d;checkreqprot=%d;"        \
> +                       "netpeer=%d;openperm=%d;extsockclass=%d;"         \
> +                       "alwaysnetwork=%d;cgroupseclabel=%d;"             \
> +                       "nnpnosuidtransition=%d;genfsseclabelsymlink=%d;";

Rather than hardcoding policy capability names here, I would recommend
using the selinux_policycap_names[] array for the names and the
selinux_state.policycap[] array for the values.  Also recommend
passing in a struct selinux_state * here to allow for future case
where there are multiple selinux states, one per selinux namespace.

> diff --git a/security/selinux/ss/services.c b/security/selinux/ss/services.c
> index ef0afd878bfc..0c289d13ef6a 100644
> --- a/security/selinux/ss/services.c
> +++ b/security/selinux/ss/services.c
> @@ -3724,10 +3724,11 @@ int security_netlbl_sid_to_secattr(struct selinux_state *state,
>   * security_read_policy - read the policy.
>   * @data: binary policy data
>   * @len: length of data in bytes
> - *
> + * @alloc_kernel_memory: flag to indicate memory allocation
>   */
> -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,
> +                                bool alloc_kernel_memory)

Instead of passing in a boolean to control how the memory is
allocated, split this into a helper function that takes an
already-allocated buffer and two
different front-end wrappers, one for kernel-internal use and one for
userspace use.

> @@ -3738,7 +3739,10 @@ int security_read_policy(struct selinux_state *state,
>
>         *len = security_policydb_len(state);
>
> -       *data = vmalloc_user(*len);
> +       if (alloc_kernel_memory)
> +               *data = kzalloc(*len, GFP_KERNEL);

You need vmalloc() since policy image size may exceed kmalloc max (or
at least that used to be the case).
Lakshmi Ramasubramanian July 15, 2020, 6:34 p.m. UTC | #2
On 7/15/20 11:04 AM, Stephen Smalley wrote:

>> +static inline bool selinux_checkreqprot(void)
>> +{
>> +       struct selinux_state *state = &selinux_state;
>> +
>> +       return state->checkreqprot;
>> +}
> 
> Probably should use READ_ONCE().
Will do.

> 
>> diff --git a/security/selinux/measure.c b/security/selinux/measure.c
>> new file mode 100644
>> index 000000000000..b909e8e61542
>> --- /dev/null
>> +++ b/security/selinux/measure.c
>> @@ -0,0 +1,122 @@
>> +int selinux_security_state(void)
> 
> Let's call this selinux_measure_state() or similar.  Needs a verb. And
> pass it a struct selinux_state * pointer argument to be measured, even
> though initially it will always be passed &selinux_state.  The
> encapsulation of selinux state within selinux_state was to support
> multiple selinux namespaces in the future, each with their own state.
Will do.

>> +       static char *security_state_string =
>> +                       "enabled=%d;enforcing=%d;checkreqprot=%d;"        \
>> +                       "netpeer=%d;openperm=%d;extsockclass=%d;"         \
>> +                       "alwaysnetwork=%d;cgroupseclabel=%d;"             \
>> +                       "nnpnosuidtransition=%d;genfsseclabelsymlink=%d;";
> 
> Rather than hardcoding policy capability names here, I would recommend
> using the selinux_policycap_names[] array for the names and the
> selinux_state.policycap[] array for the values.  Also recommend
> passing in a struct selinux_state * here to allow for future case
> where there are multiple selinux states, one per selinux namespace.
Will do.

> 
>> diff --git a/security/selinux/ss/services.c b/security/selinux/ss/services.c
>> index ef0afd878bfc..0c289d13ef6a 100644
>> --- a/security/selinux/ss/services.c
>> +++ b/security/selinux/ss/services.c
>> @@ -3724,10 +3724,11 @@ int security_netlbl_sid_to_secattr(struct selinux_state *state,
>>    * security_read_policy - read the policy.
>>    * @data: binary policy data
>>    * @len: length of data in bytes
>> - *
>> + * @alloc_kernel_memory: flag to indicate memory allocation
>>    */
>> -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,
>> +                                bool alloc_kernel_memory)
> 
> Instead of passing in a boolean to control how the memory is
> allocated, split this into a helper function that takes an
> already-allocated buffer and two
> different front-end wrappers, one for kernel-internal use and one for
> userspace use.
Will do.

> 
>> @@ -3738,7 +3739,10 @@ int security_read_policy(struct selinux_state *state,
>>
>>          *len = security_policydb_len(state);
>>
>> -       *data = vmalloc_user(*len);
>> +       if (alloc_kernel_memory)
>> +               *data = kzalloc(*len, GFP_KERNEL);
> 
> You need vmalloc() since policy image size may exceed kmalloc max (or
> at least that used to be the case).
Will do.

thanks,
  -lakshmi
diff mbox series

Patch

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..1f270206f0ee 100644
--- a/security/selinux/hooks.c
+++ b/security/selinux/hooks.c
@@ -7284,6 +7284,7 @@  DEFINE_LSM(selinux) = {
 	.enabled = &selinux_enabled_boot,
 	.blobs = &selinux_blob_sizes,
 	.init = selinux_init,
+	.security_state = selinux_security_state,
 };
 
 #if defined(CONFIG_NETFILTER)
@@ -7394,6 +7395,7 @@  int selinux_disable(struct selinux_state *state)
 	}
 
 	selinux_mark_disabled(state);
+	selinux_security_state();
 
 	pr_info("SELinux:  Disabled at runtime.\n");
 
diff --git a/security/selinux/include/security.h b/security/selinux/include/security.h
index b0e02cfe3ce1..691c7e35f82a 100644
--- a/security/selinux/include/security.h
+++ b/security/selinux/include/security.h
@@ -222,16 +222,35 @@  static inline bool selinux_policycap_genfs_seclabel_symlinks(void)
 	return state->policycap[POLICYDB_CAPABILITY_GENFS_SECLABEL_SYMLINKS];
 }
 
+static inline bool selinux_checkreqprot(void)
+{
+	struct selinux_state *state = &selinux_state;
+
+	return 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_selinux_policy(struct selinux_state *state,
+				 void **data, size_t *len,
+				 bool alloc_kernel_memory);
 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 int selinux_security_state(void);
+#else
+static inline int selinux_security_state(void)
+{
+	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..b909e8e61542
--- /dev/null
+++ b/security/selinux/measure.c
@@ -0,0 +1,122 @@ 
+// SPDX-License-Identifier: GPL-2.0-or-later
+/*
+ * Measure SELinux state using IMA subsystem.
+ */
+#include <linux/ima.h>
+#include "security.h"
+
+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_security_state(void)
+{
+	int rc = 0;
+	int count;
+	size_t buflen;
+	int policy_hash_len;
+	char *state = NULL;
+	void *policy = NULL;
+	void *policy_hash = NULL;
+	static char *security_state_string =
+			"enabled=%d;enforcing=%d;checkreqprot=%d;"        \
+			"netpeer=%d;openperm=%d;extsockclass=%d;"         \
+			"alwaysnetwork=%d;cgroupseclabel=%d;"             \
+			"nnpnosuidtransition=%d;genfsseclabelsymlink=%d;";
+
+	if (!selinux_initialized(&selinux_state))
+		return -EOPNOTSUPP;
+
+	buflen = strlen(security_state_string) + 1;
+	state = kzalloc(buflen, GFP_KERNEL);
+	if (!state) {
+		rc = -ENOMEM;
+		goto out;
+	}
+
+	count = snprintf(state, buflen, security_state_string,
+			 !selinux_disabled(&selinux_state),
+			 enforcing_enabled(&selinux_state),
+			 selinux_checkreqprot(),
+			 selinux_policycap_netpeer(),
+			 selinux_policycap_openperm(),
+			 selinux_policycap_extsockclass(),
+			 selinux_policycap_alwaysnetwork(),
+			 selinux_policycap_cgroupseclabel(),
+			 selinux_policycap_nnp_nosuid_transition(),
+			 selinux_policycap_genfs_seclabel_symlinks());
+	if (count >= 0 && count < buflen)
+		ima_lsm_state("selinux-state", state, count);
+	else {
+		pr_err("selinux state error: %d\n", count);
+		rc = -EINVAL;
+		goto out;
+	}
+
+	rc = security_read_selinux_policy(&selinux_state,
+					  &policy, &buflen, true);
+	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:
+	kfree(state);
+	kfree(policy);
+	kfree(policy_hash);
+
+	if (rc)
+		pr_err("%s: error %d\n", __func__, rc);
+
+	return rc;
+}
diff --git a/security/selinux/selinuxfs.c b/security/selinux/selinuxfs.c
index 4781314c2510..8f68964e4ba8 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_security_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..0c289d13ef6a 100644
--- a/security/selinux/ss/services.c
+++ b/security/selinux/ss/services.c
@@ -3724,10 +3724,11 @@  int security_netlbl_sid_to_secattr(struct selinux_state *state,
  * security_read_policy - read the policy.
  * @data: binary policy data
  * @len: length of data in bytes
- *
+ * @alloc_kernel_memory: flag to indicate memory allocation
  */
-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,
+				 bool alloc_kernel_memory)
 {
 	struct policydb *policydb = &state->ss->policydb;
 	int rc;
@@ -3738,7 +3739,10 @@  int security_read_policy(struct selinux_state *state,
 
 	*len = security_policydb_len(state);
 
-	*data = vmalloc_user(*len);
+	if (alloc_kernel_memory)
+		*data = kzalloc(*len, GFP_KERNEL);
+	else
+		*data = vmalloc_user(*len);
 	if (!*data)
 		return -ENOMEM;
 
@@ -3754,5 +3758,16 @@  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)
+{
+	return security_read_selinux_policy(state, data, len, false);
 }