x25: Patch to fix bug 15678 - x25 accesses fields beyond end of packet.

Here is a patch to stop X.25 examining fields beyond the end of the packet.

For example, when a simple CALL ACCEPTED was received:

	10 10 0f

x25_parse_facilities was attempting to decode the FACILITIES field, but this
packet contains no facilities field.

Signed-off-by: John Hughes <john@calva.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 46 insertions, 1 deletions

diff --git a/net/x25/af_x25.c b/net/x25/af_x25.c
index 9796f3e..fe26c01 100644
--- a/net/x25/af_x25.c
+++ b/net/x25/af_x25.c
@@ -82,6 +82,41 @@ struct compat_x25_subscrip_struct {
 };
 #endif
 
+
+int x25_parse_address_block(struct sk_buff *skb,
+		struct x25_address *called_addr,
+		struct x25_address *calling_addr)
+{
+	unsigned char len;
+	int needed;
+	int rc;
+
+	if (skb->len < 1) {
+		/* packet has no address block */
+		rc = 0;
+		goto empty;
+	}
+
+	len = *skb->data;
+	needed = 1 + (len >> 4) + (len & 0x0f);
+
+	if (skb->len < needed) {
+		/* packet is too short to hold the addresses it claims
+		   to hold */
+		rc = -1;
+		goto empty;
+	}
+
+	return x25_addr_ntoa(skb->data, called_addr, calling_addr);
+
+empty:
+	*called_addr->x25_addr = 0;
+	*calling_addr->x25_addr = 0;
+
+	return rc;
+}
+
+
 int x25_addr_ntoa(unsigned char *p, struct x25_address *called_addr,
 		  struct x25_address *calling_addr)
 {
@@ -921,16 +956,26 @@ int x25_rx_call_request(struct sk_buff *skb, struct x25_neigh *nb,
 	/*
 	 *	Extract the X.25 addresses and convert them to ASCII strings,
 	 *	and remove them.
+	 *
+	 *	Address block is mandatory in call request packets
 	 */
-	addr_len = x25_addr_ntoa(skb->data, &source_addr, &dest_addr);
+	addr_len = x25_parse_address_block(skb, &source_addr, &dest_addr);
+	if (addr_len <= 0)
+		goto out_clear_request;
 	skb_pull(skb, addr_len);
 
 	/*
 	 *	Get the length of the facilities, skip past them for the moment
 	 *	get the call user data because this is needed to determine
 	 *	the correct listener
+	 *
+	 *	Facilities length is mandatory in call request packets
 	 */
+	if (skb->len < 1)
+		goto out_clear_request;
 	len = skb->data[0] + 1;
+	if (skb->len < len)
+		goto out_clear_request;
 	skb_pull(skb,len);
 
 	/*