ima: add policy support for file system uuid

The IMA policy permits specifying rules to enable or disable
measurement/appraisal/audit based on the file system magic number.
If, for example, the policy contains an ext4 measurement rule,
the rule is enabled for all ext4 partitions.

Sometimes it might be necessary to enable measurement/appraisal/audit
only for one partition and disable it for another partition of the
same type.  With the existing IMA policy syntax, this can not be done.

This patch provides support for IMA policy rules to specify the file
system by its UUID (eg. fsuuid=397449cd-687d-4145-8698-7fed4a3e0363).

For partitions not being appraised, it might be a good idea to mount
file systems with the 'noexec' option to prevent executing non-verified
binaries.

Signed-off-by: Dmitry Kasatkin <[email protected]>
Signed-off-by: Mimi Zohar <[email protected]>

Documentation/ABI/testing/ima_policy

@@ -19,14 +19,16 @@ Description:
 
 		action: measure | dont_measure | appraise | dont_appraise | audit
 		condition:= base | lsm  [option]
-			base:	[[func=] [mask=] [fsmagic=] [uid=] [fowner]]
+			base:	[[func=] [mask=] [fsmagic=] [fsuuid=] [uid=]
+				 [fowner]]
 			lsm:	[[subj_user=] [subj_role=] [subj_type=]
 				 [obj_user=] [obj_role=] [obj_type=]]
 			option:	[[appraise_type=]]
 
 		base: 	func:= [BPRM_CHECK][MMAP_CHECK][FILE_CHECK][MODULE_CHECK]
 			mask:= [MAY_READ] [MAY_WRITE] [MAY_APPEND] [MAY_EXEC]
 			fsmagic:= hex value
+			fsuuid:= file system UUID (e.g 8bcbe394-4f13-4144-be8e-5aa9ea2ce2f6)
 			uid:= decimal value
 			fowner:=decimal value
 		lsm:  	are LSM specific

security/integrity/ima/ima_policy.c

@@ -16,6 +16,7 @@
 #include <linux/magic.h>
 #include <linux/parser.h>
 #include <linux/slab.h>
+#include <linux/genhd.h>
 
 #include "ima.h"
 
@@ -25,6 +26,7 @@
 #define IMA_FSMAGIC	0x0004
 #define IMA_UID		0x0008
 #define IMA_FOWNER	0x0010
+#define IMA_FSUUID	0x0020
 
 #define UNKNOWN		0
 #define MEASURE		0x0001	/* same as IMA_MEASURE */
@@ -45,6 +47,7 @@ struct ima_rule_entry {
 	enum ima_hooks func;
 	int mask;
 	unsigned long fsmagic;
+	u8 fsuuid[16];
 	kuid_t uid;
 	kuid_t fowner;
 	struct {
@@ -172,6 +175,9 @@ static bool ima_match_rules(struct ima_rule_entry *rule,
 	if ((rule->flags & IMA_FSMAGIC)
 	    && rule->fsmagic != inode->i_sb->s_magic)
 		return false;
+	if ((rule->flags & IMA_FSUUID) &&
+		memcmp(rule->fsuuid, inode->i_sb->s_uuid, sizeof(rule->fsuuid)))
+		return false;
 	if ((rule->flags & IMA_UID) && !uid_eq(rule->uid, cred->uid))
 		return false;
 	if ((rule->flags & IMA_FOWNER) && !uid_eq(rule->fowner, inode->i_uid))
@@ -346,7 +352,7 @@ enum {
 	Opt_obj_user, Opt_obj_role, Opt_obj_type,
 	Opt_subj_user, Opt_subj_role, Opt_subj_type,
 	Opt_func, Opt_mask, Opt_fsmagic, Opt_uid, Opt_fowner,
-	Opt_appraise_type
+	Opt_appraise_type, Opt_fsuuid
 };
 
 static match_table_t policy_tokens = {
@@ -364,6 +370,7 @@ static match_table_t policy_tokens = {
 	{Opt_func, "func=%s"},
 	{Opt_mask, "mask=%s"},
 	{Opt_fsmagic, "fsmagic=%s"},
+	{Opt_fsuuid, "fsuuid=%s"},
 	{Opt_uid, "uid=%s"},
 	{Opt_fowner, "fowner=%s"},
 	{Opt_appraise_type, "appraise_type=%s"},
@@ -519,6 +526,19 @@ static int ima_parse_rule(char *rule, struct ima_rule_entry *entry)
 			if (!result)
 				entry->flags |= IMA_FSMAGIC;
 			break;
+		case Opt_fsuuid:
+			ima_log_string(ab, "fsuuid", args[0].from);
+
+			if (memchr_inv(entry->fsuuid, 0x00,
+			    sizeof(entry->fsuuid))) {
+				result = -EINVAL;
+				break;
+			}
+
+			part_pack_uuid(args[0].from, entry->fsuuid);
+			entry->flags |= IMA_FSUUID;
+			result = 0;
+			break;
 		case Opt_uid:
 			ima_log_string(ab, "uid", args[0].from);