[PATCH v2 1/2] selinux: add brief info to policydb

[Sebastien Buisson]

Add policybrief field to struct policydb. It holds a brief info
of the policydb, in the following form:
<0 or 1 for enforce>:<0 or 1 for checkreqprot>:<hashalg>=<checksum>
Policy brief is computed every time the policy is loaded, and when
enforce or checkreqprot are changed.

Add security_policy_brief hook to give access to policy brief to
the rest of the kernel. Lustre client makes use of this information.

Signed-off-by: Sebastien Buisson <sbuisson@xxxxxxx>
---
 include/linux/lsm_hooks.h           |  2 +
 include/linux/security.h            |  7 ++++
 security/security.c                 |  6 +++
 security/selinux/hooks.c            | 11 +++++-
 security/selinux/include/security.h |  2 +
 security/selinux/selinuxfs.c        |  6 ++-
 security/selinux/ss/policydb.c      | 70 +++++++++++++++++++++++++++++++++++
 security/selinux/ss/policydb.h      |  3 ++
 security/selinux/ss/services.c      | 73 +++++++++++++++++++++++++++++++++++++
 9 files changed, 178 insertions(+), 2 deletions(-)

diff --git a/include/linux/lsm_hooks.h b/include/linux/lsm_hooks.h
index 080f34e..7139a07 100644
--- a/include/linux/lsm_hooks.h
+++ b/include/linux/lsm_hooks.h
@@ -1568,6 +1568,7 @@
 	int (*inode_setsecctx)(struct dentry *dentry, void *ctx, u32 ctxlen);
 	int (*inode_getsecctx)(struct inode *inode, void **ctx, u32 *ctxlen);
 
+	int (*policy_brief)(char **brief, size_t *len, bool alloc);
 #ifdef CONFIG_SECURITY_NETWORK
 	int (*unix_stream_connect)(struct sock *sock, struct sock *other,
 					struct sock *newsk);
@@ -1813,6 +1814,7 @@ struct security_hook_heads {
 	struct list_head inode_notifysecctx;
 	struct list_head inode_setsecctx;
 	struct list_head inode_getsecctx;
+	struct list_head policy_brief;
 #ifdef CONFIG_SECURITY_NETWORK
 	struct list_head unix_stream_connect;
 	struct list_head unix_may_send;
diff --git a/include/linux/security.h b/include/linux/security.h
index af675b5..3b72053 100644
--- a/include/linux/security.h
+++ b/include/linux/security.h
@@ -377,6 +377,8 @@ int security_sem_semop(struct sem_array *sma, struct sembuf *sops,
 int security_inode_notifysecctx(struct inode *inode, void *ctx, u32 ctxlen);
 int security_inode_setsecctx(struct dentry *dentry, void *ctx, u32 ctxlen);
 int security_inode_getsecctx(struct inode *inode, void **ctx, u32 *ctxlen);
+
+int security_policy_brief(char **brief, size_t *len, bool alloc);
 #else /* CONFIG_SECURITY */
 struct security_mnt_opts {
 };
@@ -1166,6 +1168,11 @@ static inline int security_inode_getsecctx(struct inode *inode, void **ctx, u32
 {
 	return -EOPNOTSUPP;
 }
+
+static inline int security_policy_brief(char **brief, size_t *len, bool alloc)
+{
+	return -EOPNOTSUPP;
+}
 #endif	/* CONFIG_SECURITY */
 
 #ifdef CONFIG_SECURITY_NETWORK
diff --git a/security/security.c b/security/security.c
index b9fea39..954b391 100644
--- a/security/security.c
+++ b/security/security.c
@@ -1285,6 +1285,12 @@ int security_inode_getsecctx(struct inode *inode, void **ctx, u32 *ctxlen)
 }
 EXPORT_SYMBOL(security_inode_getsecctx);
 
+int security_policy_brief(char **brief, size_t *len, bool alloc)
+{
+	return call_int_hook(policy_brief, -EOPNOTSUPP, brief, len, alloc);
+}
+EXPORT_SYMBOL(security_policy_brief);
+
 #ifdef CONFIG_SECURITY_NETWORK
 
 int security_unix_stream_connect(struct sock *sock, struct sock *other, struct sock *newsk)
diff --git a/security/selinux/hooks.c b/security/selinux/hooks.c
index e67a526..b4dd605 100644
--- a/security/selinux/hooks.c
+++ b/security/selinux/hooks.c
@@ -104,8 +104,10 @@
 static int __init enforcing_setup(char *str)
 {
 	unsigned long enforcing;
-	if (!kstrtoul(str, 0, &enforcing))
+	if (!kstrtoul(str, 0, &enforcing)) {
 		selinux_enforcing = enforcing ? 1 : 0;
+		security_policydb_update_info(NULL);
+	}
 	return 1;
 }
 __setup("enforcing=", enforcing_setup);
@@ -6063,6 +6065,11 @@ static int selinux_inode_getsecctx(struct inode *inode, void **ctx, u32 *ctxlen)
 	*ctxlen = len;
 	return 0;
 }
+
+static int selinux_policy_brief(char **brief, size_t *len, bool alloc)
+{
+	return security_policydb_brief(brief, len, alloc);
+}
 #ifdef CONFIG_KEYS
 
 static int selinux_key_alloc(struct key *k, const struct cred *cred,
@@ -6277,6 +6284,8 @@ static int selinux_key_getsecurity(struct key *key, char **_buffer)
 	LSM_HOOK_INIT(inode_setsecctx, selinux_inode_setsecctx),
 	LSM_HOOK_INIT(inode_getsecctx, selinux_inode_getsecctx),
 
+	LSM_HOOK_INIT(policy_brief, selinux_policy_brief),
+
 	LSM_HOOK_INIT(unix_stream_connect, selinux_socket_unix_stream_connect),
 	LSM_HOOK_INIT(unix_may_send, selinux_socket_unix_may_send),
 
diff --git a/security/selinux/include/security.h b/security/selinux/include/security.h
index f979c35..167e274 100644
--- a/security/selinux/include/security.h
+++ b/security/selinux/include/security.h
@@ -97,6 +97,8 @@ enum {
 int security_load_policy(void *data, size_t len);
 int security_read_policy(void **data, size_t *len);
 size_t security_policydb_len(void);
+int security_policydb_brief(char **brief, size_t *len, bool alloc);
+void security_policydb_update_info(void *p);
 
 int security_policycap_supported(unsigned int req_cap);
 
diff --git a/security/selinux/selinuxfs.c b/security/selinux/selinuxfs.c
index ce71718..b959ee7 100644
--- a/security/selinux/selinuxfs.c
+++ b/security/selinux/selinuxfs.c
@@ -55,8 +55,10 @@
 static int __init checkreqprot_setup(char *str)
 {
 	unsigned long checkreqprot;
-	if (!kstrtoul(str, 0, &checkreqprot))
+	if (!kstrtoul(str, 0, &checkreqprot)) {
 		selinux_checkreqprot = checkreqprot ? 1 : 0;
+		security_policydb_update_info(NULL);
+	}
 	return 1;
 }
 __setup("checkreqprot=", checkreqprot_setup);
@@ -159,6 +161,7 @@ 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));
 		selinux_enforcing = new_value;
+		security_policydb_update_info(NULL);
 		if (selinux_enforcing)
 			avc_ss_reset(0);
 		selnl_notify_setenforce(selinux_enforcing);
@@ -621,6 +624,7 @@ static ssize_t sel_write_checkreqprot(struct file *file, const char __user *buf,
 		goto out;
 
 	selinux_checkreqprot = new_value ? 1 : 0;
+	security_policydb_update_info(NULL);
 	length = count;
 out:
 	kfree(page);
diff --git a/security/selinux/ss/policydb.c b/security/selinux/ss/policydb.c
index 0080122..9eb2f82 100644
--- a/security/selinux/ss/policydb.c
+++ b/security/selinux/ss/policydb.c
@@ -32,6 +32,8 @@
 #include <linux/errno.h>
 #include <linux/audit.h>
 #include <linux/flex_array.h>
+#include <crypto/hash.h>
+#include <crypto/sha.h>
 #include "security.h"
 
 #include "policydb.h"
@@ -879,6 +881,8 @@ void policydb_destroy(struct policydb *p)
 	ebitmap_destroy(&p->filename_trans_ttypes);
 	ebitmap_destroy(&p->policycaps);
 	ebitmap_destroy(&p->permissive_map);
+
+	kfree(p->policybrief);
 }
 
 /*
@@ -2220,6 +2224,67 @@ static int ocontext_read(struct policydb *p, struct policydb_compat_info *info,
 }
 
 /*
+ * Compute summary of a policy database binary representation file,
+ * and store it into a policy database structure.
+ */
+static int policydb_brief(struct policydb *policydb, void *ptr)
+{
+	struct policy_file *fp = ptr;
+	struct crypto_shash *tfm;
+	char hashalg[] = "sha256";
+	int hashsize = SHA256_DIGEST_SIZE;
+	char hashval[hashsize];
+	int idx;
+	unsigned char *p;
+
+	if (policydb->policybrief)
+		return -EINVAL;
+
+	tfm = crypto_alloc_shash(hashalg, 0, 0);
+	if (IS_ERR(tfm)) {
+		printk(KERN_ERR "Failed to alloc crypto hash %s\n", hashalg);
+		return PTR_ERR(tfm);
+	}
+
+	{
+		int rc;
+
+		SHASH_DESC_ON_STACK(desc, tfm);
+		desc->tfm = tfm;
+		desc->flags = 0;
+		rc = crypto_shash_init(desc);
+		if (rc) {
+			printk(KERN_ERR "Failed to init shash\n");
+			crypto_free_shash(tfm);
+			return rc;
+		}
+
+		crypto_shash_update(desc, fp->data, fp->len);
+		crypto_shash_final(desc, hashval);
+		crypto_free_shash(tfm);
+	}
+
+	/* policy brief is in the form:
+	 * <0 or 1 for enforce>:<0 or 1 for checkreqprot>:<hashalg>=<checksum>
+	 */
+	policydb->policybrief = kzalloc(5 + strlen(hashalg) + 2*hashsize + 1,
+					GFP_KERNEL);
+	if (policydb->policybrief == NULL)
+		return -ENOMEM;
+
+	sprintf(policydb->policybrief, "x:x:%s=", hashalg);
+	security_policydb_update_info(policydb);
+	p = policydb->policybrief + strlen(policydb->policybrief);
+	for (idx = 0; idx < hashsize; idx++) {
+		snprintf(p, 3, "%02x", (unsigned char)(hashval[idx]));
+		p += 2;
+	}
+	policydb->policybrief_len = (size_t)(p - policydb->policybrief);
+
+	return 0;
+}
+
+/*
  * Read the configuration data from a policy database binary
  * representation file into a policy database structure.
  */
@@ -2238,6 +2303,11 @@ int policydb_read(struct policydb *p, void *fp)
 	if (rc)
 		return rc;
 
+	/* Compute sumarry of policy, and store it in policydb */
+	rc = policydb_brief(p, fp);
+	if (rc)
+		goto bad;
+
 	/* Read the magic number and string length. */
 	rc = next_entry(buf, fp, sizeof(u32) * 2);
 	if (rc)
diff --git a/security/selinux/ss/policydb.h b/security/selinux/ss/policydb.h
index 725d594..1fca438 100644
--- a/security/selinux/ss/policydb.h
+++ b/security/selinux/ss/policydb.h
@@ -293,6 +293,9 @@ struct policydb {
 	size_t len;
 
 	unsigned int policyvers;
+	/* summary computed on the policy */
+	unsigned char *policybrief;
+	size_t policybrief_len;
 
 	unsigned int reject_unknown : 1;
 	unsigned int allow_unknown : 1;
diff --git a/security/selinux/ss/services.c b/security/selinux/ss/services.c
index 60d9b02..9a94f8e 100644
--- a/security/selinux/ss/services.c
+++ b/security/selinux/ss/services.c
@@ -2170,6 +2170,79 @@ size_t security_policydb_len(void)
 }
 
 /**
+ * security_policydb_brief - Get policydb brief
+ * @brief: pointer to buffer holding brief
+ * @len: in: brief buffer length if no alloc, out: brief string len
+ * @alloc: whether to allocate buffer for brief or not
+ *
+ * On success 0 is returned , or negative value on error.
+ **/
+int security_policydb_brief(char **brief, size_t *len, bool alloc)
+{
+	int rc = 0;
+	size_t policybrief_len;
+
+	if (brief == NULL)
+		return -EINVAL;
+
+	read_lock(&policy_rwlock);
+	policybrief_len = policydb.policybrief_len;
+	if (policydb.policybrief == NULL)
+		rc = -EAGAIN;
+	read_unlock(&policy_rwlock);
+
+	if (rc)
+		return rc;
+
+	if (alloc)
+		/* *brief must be kfreed by caller in this case */
+		*brief = kzalloc(policybrief_len + 1, GFP_KERNEL);
+	else
+		/*
+		 * if !alloc, caller must pass a buffer that
+		 * can hold policybrief_len+1 chars
+		 */
+		if (*len < policybrief_len + 1) {
+			/* put in *len the string size we need to write */
+			*len = policybrief_len;
+			return -ENAMETOOLONG;
+		}
+
+	if (*brief == NULL)
+		return -ENOMEM;
+
+	read_lock(&policy_rwlock);
+	strncpy(*brief, policydb.policybrief, policydb.policybrief_len);
+	*len = policydb.policybrief_len;
+	read_unlock(&policy_rwlock);
+
+	return rc;
+}
+
+void security_policydb_update_info(void *p)
+{
+	/* policy brief is in the form:
+	 * <0 or 1 for enforce>:<0 or 1 for checkreqprot>:<hashalg>=<checksum>
+	 */
+	if (p) {
+		struct policydb *poldb = p;
+		/* update policydb given as parameter if possible */
+		if (poldb->policybrief) {
+			poldb->policybrief[0] = '0' + selinux_enforcing;
+			poldb->policybrief[2] = '0' + selinux_checkreqprot;
+		}
+	} else {
+		/* update global policydb, needs write lock */
+		write_lock_irq(&policy_rwlock);
+		if (policydb.policybrief) {
+			policydb.policybrief[0] = '0' + selinux_enforcing;
+			policydb.policybrief[2] = '0' + selinux_checkreqprot;
+		}
+		write_unlock_irq(&policy_rwlock);
+	}
+}
+
+/**
  * security_port_sid - Obtain the SID for a port.
  * @protocol: protocol number
  * @port: port number
-- 
1.8.3.1