smack: Retrieve transmuting information in smack_inode_getsecurity()

Enhance smack_inode_getsecurity() to retrieve the value for
SMACK64TRANSMUTE from the inode security blob, similarly to SMACK64.

This helps to display accurate values in the situation where the security
labels come from mount options and not from xattrs.
Signed-off-by: Roberto Sassu <roberto.sassu@huawei.com>
Signed-off-by: Casey Schaufler <casey@schaufler-ca.com>

security/smack/smack_lsm.c

@@ -1463,10 +1463,19 @@ static int smack_inode_getsecurity(struct mnt_idmap *idmap,
 	struct super_block *sbp;
 	struct inode *ip = inode;
 	struct smack_known *isp;
+	struct inode_smack *ispp;
+	size_t label_len;
+	char *label = NULL;
 
-	if (strcmp(name, XATTR_SMACK_SUFFIX) == 0)
+	if (strcmp(name, XATTR_SMACK_SUFFIX) == 0) {
 		isp = smk_of_inode(inode);
-	else {
+	} else if (strcmp(name, XATTR_SMACK_TRANSMUTE) == 0) {
+		ispp = smack_inode(inode);
+		if (ispp->smk_flags & SMK_INODE_TRANSMUTE)
+			label = TRANS_TRUE;
+		else
+			label = "";
+	} else {
 		/*
 		 * The rest of the Smack xattrs are only on sockets.
 		 */
@@ -1488,13 +1497,18 @@ static int smack_inode_getsecurity(struct mnt_idmap *idmap,
 			return -EOPNOTSUPP;
 	}
 
+	if (!label)
+		label = isp->smk_known;
+
+	label_len = strlen(label);
+
 	if (alloc) {
-		*buffer = kstrdup(isp->smk_known, GFP_KERNEL);
+		*buffer = kstrdup(label, GFP_KERNEL);
 		if (*buffer == NULL)
 			return -ENOMEM;
 	}
 
-	return strlen(isp->smk_known);
+	return label_len;
 }