ima: extend the measurement list to include the file signature

This patch defines a new template called 'ima-sig', which includes
the file signature in the template data, in addition to the file's
digest and pathname.

A template is composed of a set of fields.  Associated with each
field is an initialization and display function.  This patch defines
a new template field called 'sig', the initialization function
ima_eventsig_init(), and the display function ima_show_template_sig().

This patch modifies the .field_init() function definition to include
the 'security.ima' extended attribute and length.

Changelog:
- remove unused code (Dmitry Kasatkin)
- avoid calling ima_write_template_field_data() unnecesarily (Roberto Sassu)
- rename DATA_FMT_SIG to DATA_FMT_HEX
- cleanup ima_eventsig_init() based on Roberto's comments

Signed-off-by: Mimi Zohar <zohar@linux.vnet.ibm.com>
Signed-off-by: Dmitry Kasatkin <d.kasatkin@samsung.com>
Signed-off-by: Roberto Sassu <roberto.sassu@polito.it>
diff --git a/security/integrity/ima/Kconfig b/security/integrity/ima/Kconfig
index 351a58e..81a2797 100644
--- a/security/integrity/ima/Kconfig
+++ b/security/integrity/ima/Kconfig
@@ -63,6 +63,8 @@
 		bool "ima"
 	config IMA_NG_TEMPLATE
 		bool "ima-ng (default)"
+	config IMA_SIG_TEMPLATE
+		bool "ima-sig"
 endchoice
 
 config IMA_DEFAULT_TEMPLATE
@@ -70,6 +72,7 @@
 	depends on IMA
 	default "ima" if IMA_TEMPLATE
 	default "ima-ng" if IMA_NG_TEMPLATE
+	default "ima-sig" if IMA_SIG_TEMPLATE
 
 choice
 	prompt "Default integrity hash algorithm"