smack: off by one error

commit 3b9fc372 upstream.

Consider the input case of a rule that consists entirely of non space
symbols followed by a \0. Say 64 + \0

In this case strlen(data) = 64
kzalloc of subject and object are 64 byte objects
sscanfdata, "%s %s %s", subject, ...)

will put 65 bytes into subject.
Signed-off-by: Alan Cox <alan@linux.intel.com>
Acked-by: Casey Schaufler <casey@schaufler-ca.com>
Signed-off-by: James Morris <james.l.morris@oracle.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

security/smack/smackfs.c

@@ -325,11 +325,11 @@ static int smk_parse_long_rule(const char *data, struct smack_rule *rule,
 	int datalen;
 	int rc = -1;
 
-	/*
-	 * This is probably inefficient, but safe.
-	 */
+	/* This is inefficient */
 	datalen = strlen(data);
-	subject = kzalloc(datalen, GFP_KERNEL);
+
+	/* Our first element can be 64 + \0 with no spaces */
+	subject = kzalloc(datalen + 1, GFP_KERNEL);
 	if (subject == NULL)
 		return -1;
 	object = kzalloc(datalen, GFP_KERNEL);