ima: add appraise action keywords and default rules

Unlike the IMA measurement policy, the appraise policy can not be dependent
on runtime process information, such as the task uid, as the 'security.ima'
xattr is written on file close and must be updated each time the file changes,
regardless of the current task uid.

This patch extends the policy language with 'fowner', defines an appraise
policy, which appraises all files owned by root, and defines 'ima_appraise_tcb',
a new boot command line option, to enable the appraise policy.

Changelog v3:
- separate the measure from the appraise rules in order to support measuring
  without appraising and appraising without measuring.
- change appraisal default for filesystems without xattr support to fail
- update default appraise policy for cgroups

Changelog v1:
- don't appraise RAMFS (Dmitry Kasatkin)
- merged rest of "ima: ima_must_appraise_or_measure API change" commit
  (Dmtiry Kasatkin)

  ima_must_appraise_or_measure() called ima_match_policy twice, which
  searched the policy for a matching rule.  Once for a matching measurement
  rule and subsequently for an appraisal rule. Searching the policy twice
  is unnecessary overhead, which could be noticeable with a large policy.

  The new version of ima_must_appraise_or_measure() does everything in a
  single iteration using a new version of ima_match_policy().  It returns
  IMA_MEASURE, IMA_APPRAISE mask.

  With the use of action mask only one efficient matching function
  is enough.  Removed other specific versions of matching functions.

Changelog:
- change 'owner' to 'fowner' to conform to the new LSM conditions posted by
  Roberto Sassu.
- fix calls to ima_log_string()
Signed-off-by: Mimi Zohar <zohar@us.ibm.com>
Signed-off-by: Dmitry Kasatkin <dmitry.kasatkin@intel.com>

Documentation/ABI/testing/ima_policy

@@ -12,11 +12,14 @@ Description:
 		then closing the file.  The new policy takes effect after
 		the file ima/policy is closed.
 
+		IMA appraisal, if configured, uses these file measurements
+		for local measurement appraisal.
+
 		rule format: action [condition ...]
 
-		action: measure | dont_measure
+		action: measure | dont_measure | appraise | dont_appraise
 		condition:= base | lsm
-			base:	[[func=] [mask=] [fsmagic=] [uid=]]
+			base:	[[func=] [mask=] [fsmagic=] [uid=] [fowner]]
 			lsm:	[[subj_user=] [subj_role=] [subj_type=]
 				 [obj_user=] [obj_role=] [obj_type=]]
 
@@ -24,36 +27,50 @@ Description:
 			mask:= [MAY_READ] [MAY_WRITE] [MAY_APPEND] [MAY_EXEC]
 			fsmagic:= hex value
 			uid:= decimal value
+			fowner:=decimal value
 		lsm:  	are LSM specific
 
 		default policy:
 			# PROC_SUPER_MAGIC
 			dont_measure fsmagic=0x9fa0
+			dont_appraise fsmagic=0x9fa0
 			# SYSFS_MAGIC
 			dont_measure fsmagic=0x62656572
+			dont_appraise fsmagic=0x62656572
 			# DEBUGFS_MAGIC
 			dont_measure fsmagic=0x64626720
+			dont_appraise fsmagic=0x64626720
 			# TMPFS_MAGIC
 			dont_measure fsmagic=0x01021994
+			dont_appraise fsmagic=0x01021994
+			# RAMFS_MAGIC
+			dont_measure fsmagic=0x858458f6
+			dont_appraise fsmagic=0x858458f6
 			# SECURITYFS_MAGIC
 			dont_measure fsmagic=0x73636673
+			dont_appraise fsmagic=0x73636673
 
 			measure func=BPRM_CHECK
 			measure func=FILE_MMAP mask=MAY_EXEC
 			measure func=FILE_CHECK mask=MAY_READ uid=0
+			appraise fowner=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 do_filp_open.
+		open for read by root in do_filp_open.  The default appraisal
+		policy appraises all files owned by root.
 
 		Examples of LSM specific definitions:
 
 		SELinux:
 			# SELINUX_MAGIC
-			dont_measure fsmagic=0xF97CFF8C
+			dont_measure fsmagic=0xf97cff8c
+			dont_appraise fsmagic=0xf97cff8c
 
 			dont_measure obj_type=var_log_t
+			dont_appraise obj_type=var_log_t
 			dont_measure obj_type=auditd_log_t
+			dont_appraise obj_type=auditd_log_t
 			measure subj_user=system_u func=FILE_CHECK mask=MAY_READ
 			measure subj_role=system_r func=FILE_CHECK mask=MAY_READ
 

Documentation/kernel-parameters.txt

@@ -1055,6 +1055,10 @@ bytes respectively. Such letter suffixes can also be entirely omitted.
 			Format: { "off" | "enforce" | "fix" }
 			default: "enforce"
 
+	ima_appraise_tcb [IMA]
+			The builtin appraise policy appraises all files
+			owned by uid=0.
+
 	ima_audit=	[IMA]
 			Format: { "0" | "1" }
 			0 -- integrity auditing messages. (Default)

security/integrity/ima/ima_appraise.c

@@ -36,7 +36,10 @@ __setup("ima_appraise=", default_appraise_setup);
  */
 int ima_must_appraise(struct inode *inode, enum ima_hooks func, int mask)
 {
-	return 0;
+	if (!ima_appraise)
+		return 0;
+
+	return ima_match_policy(inode, func, mask, IMA_APPRAISE);
 }
 
 static void ima_fix_xattr(struct dentry *dentry,