security: imbed evm calls in security hooks

Imbed the evm calls evm_inode_setxattr(), evm_inode_post_setxattr(),
evm_inode_removexattr() in the security hooks.  evm_inode_setxattr()
protects security.evm xattr.  evm_inode_post_setxattr() and
evm_inode_removexattr() updates the hmac associated with an inode.

(Assumes an LSM module protects the setting/removing of xattr.)

Changelog:
  - Don't define evm_verifyxattr(), unless CONFIG_INTEGRITY is enabled.
  - xattr_name is a 'const', value is 'void *'

Signed-off-by: Mimi Zohar <zohar@us.ibm.com>
Acked-by: Serge Hallyn <serge.hallyn@ubuntu.com>

include/linux/evm.h

@@ -0,0 +1,56 @@
+/*
+ * evm.h
+ *
+ * Copyright (c) 2009 IBM Corporation
+ * Author: Mimi Zohar <zohar@us.ibm.com>
+ */
+
+#ifndef _LINUX_EVM_H
+#define _LINUX_EVM_H
+
+#include <linux/integrity.h>
+
+#ifdef CONFIG_EVM
+extern enum integrity_status evm_verifyxattr(struct dentry *dentry,
+					     const char *xattr_name,
+					     void *xattr_value,
+					     size_t xattr_value_len);
+extern int evm_inode_setxattr(struct dentry *dentry, const char *name,
+			      const void *value, size_t size);
+extern void evm_inode_post_setxattr(struct dentry *dentry,
+				    const char *xattr_name,
+				    const void *xattr_value,
+				    size_t xattr_value_len);
+extern int evm_inode_removexattr(struct dentry *dentry, const char *xattr_name);
+#else
+#ifdef CONFIG_INTEGRITY
+static inline enum integrity_status evm_verifyxattr(struct dentry *dentry,
+						    const char *xattr_name,
+						    void *xattr_value,
+						    size_t xattr_value_len)
+{
+	return INTEGRITY_UNKNOWN;
+}
+#endif
+
+static inline int evm_inode_setxattr(struct dentry *dentry, const char *name,
+				     const void *value, size_t size)
+{
+	return 0;
+}
+
+static inline void evm_inode_post_setxattr(struct dentry *dentry,
+					   const char *xattr_name,
+					   const void *xattr_value,
+					   size_t xattr_value_len)
+{
+	return;
+}
+
+static inline int evm_inode_removexattr(struct dentry *dentry,
+					const char *xattr_name)
+{
+	return 0;
+}
+#endif /* CONFIG_EVM_H */
+#endif /* LINUX_EVM_H */