integrity: IMA policy

Support for a user loadable policy through securityfs
with support for LSM specific policy data.
- free invalid rule in ima_parse_add_rule()

Signed-off-by: Mimi Zohar <[email protected]>
Acked-by: Serge Hallyn <[email protected]>
Signed-off-by: James Morris <[email protected]>

Author: Mimi Zohar

Documentation/ABI/testing/ima_policy

@@ -0,0 +1,61 @@
+What:		security/ima/policy
+Date:		May 2008
+Contact:	Mimi Zohar <[email protected]>
+Description:
+		The Trusted Computing Group(TCG) runtime Integrity
+		Measurement Architecture(IMA) maintains a list of hash
+		values of executables and other sensitive system files
+		loaded into the run-time of this system.  At runtime,
+		the policy can be constrained based on LSM specific data.
+		Policies are loaded into the securityfs file ima/policy
+		by opening the file, writing the rules one at a time and
+		then closing the file.  The new policy takes effect after
+		the file ima/policy is closed.
+
+		rule format: action [condition ...]
+
+		action: measure | dont_measure
+		condition:= base | lsm
+			base:	[[func=] [mask=] [fsmagic=] [uid=]]
+			lsm:	[[subj_user=] [subj_role=] [subj_type=]
+				 [obj_user=] [obj_role=] [obj_type=]]
+
+		base: 	func:= [BPRM_CHECK][FILE_MMAP][INODE_PERMISSION]
+			mask:= [MAY_READ] [MAY_WRITE] [MAY_APPEND] [MAY_EXEC]
+			fsmagic:= hex value
+			uid:= decimal value
+		lsm:  	are LSM specific
+
+		default policy:
+			# PROC_SUPER_MAGIC
+			dont_measure fsmagic=0x9fa0
+			# SYSFS_MAGIC
+			dont_measure fsmagic=0x62656572
+			# DEBUGFS_MAGIC
+			dont_measure fsmagic=0x64626720
+			# TMPFS_MAGIC
+			dont_measure fsmagic=0x01021994
+			# SECURITYFS_MAGIC
+			dont_measure fsmagic=0x73636673
+
+			measure func=BPRM_CHECK
+			measure func=FILE_MMAP mask=MAY_EXEC
+			measure func=INODE_PERM mask=MAY_READ uid=0
+
+		The default policy measures all executables in bprm_check,
+		all files mmapped executable in file_mmap, and all files
+		open for read by root in inode_permission.
+
+		Examples of LSM specific definitions:
+
+		SELinux:
+			# SELINUX_MAGIC
+			dont_measure fsmagic=0xF97CFF8C
+
+			dont_measure obj_type=var_log_t
+			dont_measure obj_type=auditd_log_t
+			measure subj_user=system_u func=INODE_PERM mask=MAY_READ
+			measure subj_role=system_r func=INODE_PERM mask=MAY_READ
+
+		Smack:
+			measure subj_user=_ func=INODE_PERM mask=MAY_READ

security/integrity/ima/Kconfig

@@ -47,3 +47,9 @@ config IMA_AUDIT
 	  auditing messages can be enabled with 'ima_audit=1' on
 	  the kernel command line.
 
+config IMA_LSM_RULES
+	bool
+	depends on IMA && (SECURITY_SELINUX || SECURITY_SMACK)
+	default y
+	help
+	  Disabling this option will disregard LSM based policy rules

security/integrity/ima/ima.h

@@ -137,4 +137,28 @@ enum ima_hooks { PATH_CHECK = 1, FILE_MMAP, BPRM_CHECK };
 int ima_match_policy(struct inode *inode, enum ima_hooks func, int mask);
 void ima_init_policy(void);
 void ima_update_policy(void);
+int ima_parse_add_rule(char *);
+void ima_delete_rules(void);
+
+/* LSM based policy rules require audit */
+#ifdef CONFIG_IMA_LSM_RULES
+
+#define security_filter_rule_init security_audit_rule_init
+#define security_filter_rule_match security_audit_rule_match
+
+#else
+
+static inline int security_filter_rule_init(u32 field, u32 op, char *rulestr,
+					    void **lsmrule)
+{
+	return -EINVAL;
+}
+
+static inline int security_filter_rule_match(u32 secid, u32 field, u32 op,
+					     void *lsmrule,
+					     struct audit_context *actx)
+{
+	return -EINVAL;
+}
+#endif /* CONFIG_IMA_LSM_RULES */
 #endif

security/integrity/ima/ima_fs.c

@@ -19,9 +19,11 @@
 #include <linux/seq_file.h>
 #include <linux/rculist.h>
 #include <linux/rcupdate.h>
+#include <linux/parser.h>
 
 #include "ima.h"
 
+static int valid_policy = 1;
 #define TMPBUFLEN 12
 static ssize_t ima_show_htable_value(char __user *buf, size_t count,
 				     loff_t *ppos, atomic_long_t *val)
@@ -237,11 +239,66 @@ static struct file_operations ima_ascii_measurements_ops = {
 	.release = seq_release,
 };
 
+static ssize_t ima_write_policy(struct file *file, const char __user *buf,
+				size_t datalen, loff_t *ppos)
+{
+	char *data;
+	int rc;
+
+	if (datalen >= PAGE_SIZE)
+		return -ENOMEM;
+	if (*ppos != 0) {
+		/* No partial writes. */
+		return -EINVAL;
+	}
+	data = kmalloc(datalen + 1, GFP_KERNEL);
+	if (!data)
+		return -ENOMEM;
+
+	if (copy_from_user(data, buf, datalen)) {
+		kfree(data);
+		return -EFAULT;
+	}
+	*(data + datalen) = '\0';
+	rc = ima_parse_add_rule(data);
+	if (rc < 0) {
+		datalen = -EINVAL;
+		valid_policy = 0;
+	}
+
+	kfree(data);
+	return datalen;
+}
+
 static struct dentry *ima_dir;
 static struct dentry *binary_runtime_measurements;
 static struct dentry *ascii_runtime_measurements;
 static struct dentry *runtime_measurements_count;
 static struct dentry *violations;
+static struct dentry *ima_policy;
+
+/*
+ * ima_release_policy - start using the new measure policy rules.
+ *
+ * Initially, ima_measure points to the default policy rules, now
+ * point to the new policy rules, and remove the securityfs policy file.
+ */
+static int ima_release_policy(struct inode *inode, struct file *file)
+{
+	if (!valid_policy) {
+		ima_delete_rules();
+		return 0;
+	}
+	ima_update_policy();
+	securityfs_remove(ima_policy);
+	ima_policy = NULL;
+	return 0;
+}
+
+static struct file_operations ima_measure_policy_ops = {
+	.write = ima_write_policy,
+	.release = ima_release_policy
+};
 
 int ima_fs_init(void)
 {
@@ -276,13 +333,20 @@ int ima_fs_init(void)
 	if (IS_ERR(violations))
 		goto out;
 
-	return 0;
+	ima_policy = securityfs_create_file("policy",
+					    S_IRUSR | S_IRGRP | S_IWUSR,
+					    ima_dir, NULL,
+					    &ima_measure_policy_ops);
+	if (IS_ERR(ima_policy))
+		goto out;
 
+	return 0;
 out:
 	securityfs_remove(runtime_measurements_count);
 	securityfs_remove(ascii_runtime_measurements);
 	securityfs_remove(binary_runtime_measurements);
 	securityfs_remove(ima_dir);
+	securityfs_remove(ima_policy);
 	return -1;
 }
 
@@ -293,4 +357,5 @@ void __exit ima_fs_cleanup(void)
 	securityfs_remove(ascii_runtime_measurements);
 	securityfs_remove(binary_runtime_measurements);
 	securityfs_remove(ima_dir);
+	securityfs_remove(ima_policy);
 }