[PATCH V3 3/6] IMA: Allow rule matching on filesystem subtype

[Matthew Garrett <matthewgarrett@xxxxxxxxxx>]

IMA currently allows rules to match on the filesystem type. Certain
filesystem types permit subtypes (eg, fuse). Add support to IMA to allow
rules to match on subtypes as well as types.

Signed-off-by: Matthew Garrett <mjg59@xxxxxxxxxx>
---
 Documentation/ABI/testing/ima_policy |  4 +++-
 security/integrity/ima/ima_policy.c  | 26 +++++++++++++++++++++++++-
 2 files changed, 28 insertions(+), 2 deletions(-)

diff --git a/Documentation/ABI/testing/ima_policy b/Documentation/ABI/testing/ima_policy
index 74c6702de74e..09a5def7e28a 100644
--- a/Documentation/ABI/testing/ima_policy
+++ b/Documentation/ABI/testing/ima_policy
@@ -21,7 +21,7 @@ Description:
 			audit | hash | dont_hash
 		condition:= base | lsm  [option]
 			base:	[[func=] [mask=] [fsmagic=] [fsuuid=] [uid=]
-				[euid=] [fowner=] [fsname=]]
+				[euid=] [fowner=] [fsname=] [subtype=]]
 			lsm:	[[subj_user=] [subj_role=] [subj_type=]
 				 [obj_user=] [obj_role=] [obj_type=]]
 			option:	[[appraise_type=]] [permit_directio]
@@ -33,6 +33,8 @@ Description:
 			       [[^]MAY_EXEC]
 			fsmagic:= hex value
 			fsuuid:= file system UUID (e.g 8bcbe394-4f13-4144-be8e-5aa9ea2ce2f6)
+			fsname:= file system type (e.g fuse)
+			subtype:= file system subtype (e.g ntfs3g)
 			uid:= decimal value
 			euid:= decimal value
 			fowner:= decimal value
diff --git a/security/integrity/ima/ima_policy.c b/security/integrity/ima/ima_policy.c
index e0cc323f948f..bb4e265823a7 100644
--- a/security/integrity/ima/ima_policy.c
+++ b/security/integrity/ima/ima_policy.c
@@ -35,6 +35,7 @@
 #define IMA_EUID	0x0080
 #define IMA_PCR		0x0100
 #define IMA_FSNAME	0x0200
+#define IMA_SUBTYPE	0x0400
 
 #define UNKNOWN		0
 #define MEASURE		0x0001	/* same as IMA_MEASURE */
@@ -80,6 +81,7 @@ struct ima_rule_entry {
 		int type;	/* audit type */
 	} lsm[MAX_LSM_RULES];
 	char *fsname;
+	char *subtype;
 };
 
 /*
@@ -306,6 +308,10 @@ static bool ima_match_rules(struct ima_rule_entry *rule, struct inode *inode,
 	if ((rule->flags & IMA_FSNAME)
 	    && strcmp(rule->fsname, inode->i_sb->s_type->name))
 		return false;
+	if ((rule->flags & IMA_SUBTYPE)
+	    && (inode->i_sb->s_subtype == NULL ||
+		strcmp(rule->subtype, inode->i_sb->s_subtype)))
+		return false;
 	if ((rule->flags & IMA_FSUUID) &&
 	    !uuid_equal(&rule->fsuuid, &inode->i_sb->s_uuid))
 		return false;
@@ -670,7 +676,7 @@ enum {
 	Opt_audit, Opt_hash, Opt_dont_hash,
 	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_fsname,
+	Opt_func, Opt_mask, Opt_fsmagic, Opt_fsname, Opt_subtype,
 	Opt_fsuuid, Opt_uid_eq, Opt_euid_eq, Opt_fowner_eq,
 	Opt_uid_gt, Opt_euid_gt, Opt_fowner_gt,
 	Opt_uid_lt, Opt_euid_lt, Opt_fowner_lt,
@@ -696,6 +702,7 @@ static const match_table_t policy_tokens = {
 	{Opt_mask, "mask=%s"},
 	{Opt_fsmagic, "fsmagic=%s"},
 	{Opt_fsname, "fsname=%s"},
+	{Opt_subtype, "subtype=%s"},
 	{Opt_fsuuid, "fsuuid=%s"},
 	{Opt_uid_eq, "uid=%s"},
 	{Opt_euid_eq, "euid=%s"},
@@ -921,6 +928,17 @@ static int ima_parse_rule(char *rule, struct ima_rule_entry *entry)
 			result = 0;
 			entry->flags |= IMA_FSNAME;
 			break;
+		case Opt_subtype:
+			ima_log_string(ab, "subtype", args[0].from);
+
+			entry->subtype = kstrdup(args[0].from, GFP_KERNEL);
+			if (!entry->subtype) {
+				result = -ENOMEM;
+				break;
+			}
+			result = 0;
+			entry->flags |= IMA_SUBTYPE;
+			break;
 		case Opt_fsuuid:
 			ima_log_string(ab, "fsuuid", args[0].from);
 
@@ -1256,6 +1274,12 @@ int ima_policy_show(struct seq_file *m, void *v)
 		seq_puts(m, " ");
 	}
 
+	if (entry->flags & IMA_SUBTYPE) {
+		snprintf(tbuf, sizeof(tbuf), "%s", entry->subtype);
+		seq_printf(m, pt(Opt_subtype), tbuf);
+		seq_puts(m, " ");
+	}
+
 	if (entry->flags & IMA_PCR) {
 		snprintf(tbuf, sizeof(tbuf), "%d", entry->pcr);
 		seq_printf(m, pt(Opt_pcr), tbuf);
-- 
2.21.0.1020.gf2820cf01a-goog