selinux: set next pointer before attaching to list

Set the next pointer in filename_trans_read_helper() before attaching
the new node under construction to the list, otherwise garbage would be
dereferenced on subsequent failure during cleanup in the out goto label.

Cc: <stable@vger.kernel.org>
Fixes: 4300590 ("selinux: implement new format of filename transitions")
Signed-off-by: Christian Göttsche <cgzones@googlemail.com>
Signed-off-by: Paul Moore <paul@paul-moore.com>

Author: cgzones

security/selinux/ss/policydb.c

@@ -2005,6 +2005,7 @@ static int filename_trans_read_helper(struct policydb *p, void *fp)
 		if (!datum)
 			goto out;
 
+		datum->next = NULL;
 		*dst = datum;
 
 		/* ebitmap_read() will at least init the bitmap */
@@ -2017,7 +2018,6 @@ static int filename_trans_read_helper(struct policydb *p, void *fp)
 			goto out;
 
 		datum->otype = le32_to_cpu(buf[0]);
-		datum->next = NULL;
 
 		dst = &datum->next;
 	}