cipso: unsigned buf_len cannot be negative

unsigned buf_len cannot be negative
Signed-off-by: Roel Kluin <roel.kluin@gmail.com>
Signed-off-by: Paul Moore <paul.moore@hp.com>

net/ipv4/cipso_ipv4.c

@@ -2063,9 +2063,10 @@ int cipso_v4_skbuff_setattr(struct sk_buff *skb,
 	u32 opt_len;
 	int len_delta;
 
-	buf_len = cipso_v4_genopt(buf, buf_len, doi_def, secattr);
-	if (buf_len < 0)
-		return buf_len;
+	ret_val = cipso_v4_genopt(buf, buf_len, doi_def, secattr);
+	if (ret_val < 0)
+		return ret_val;
+	buf_len = ret_val;
 	opt_len = (buf_len + 3) & ~3;
 
 	/* we overwrite any existing options to ensure that we have enough