x25: possible skb leak on bad facilities

Originally x25_parse_facilities returned
-1 for an error
 0 meaning 0 length facilities
>0 the length of the facilities parsed.

5ef41308 ("x25: Prevent crashing when parsing bad X.25 facilities") introduced more
error checking in x25_parse_facilities however used 0 to indicate bad parsing
a6331d6f ("memory corruption in X.25 facilities parsing") followed this further for
DTE facilities, again using 0 for bad parsing.

The meaning of 0 got confused in the callers.
If the facilities are messed up we can't determine where the data starts.
So patch makes all parsing errors return -1 and ensures callers close and don't use the skb further.
Reported-by: Andy Whitcroft <apw@canonical.com>
Signed-off-by: Andrew Hendry <andrew.hendry@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/x25/x25_facilities.c

@@ -27,9 +27,19 @@
 #include <net/sock.h>
 #include <net/x25.h>
 
-/*
- * Parse a set of facilities into the facilities structures. Unrecognised
- *	facilities are written to the debug log file.
+/**
+ * x25_parse_facilities - Parse facilities from skb into the facilities structs
+ *
+ * @skb: sk_buff to parse
+ * @facilities: Regular facilites, updated as facilities are found
+ * @dte_facs: ITU DTE facilities, updated as DTE facilities are found
+ * @vc_fac_mask: mask is updated with all facilities found
+ *
+ * Return codes:
+ *  -1 - Parsing error, caller should drop call and clean up
+ *   0 - Parse OK, this skb has no facilities
+ *  >0 - Parse OK, returns the length of the facilities header
+ *
  */
 int x25_parse_facilities(struct sk_buff *skb, struct x25_facilities *facilities,
 		struct x25_dte_facilities *dte_facs, unsigned long *vc_fac_mask)
@@ -62,7 +72,7 @@ int x25_parse_facilities(struct sk_buff *skb, struct x25_facilities *facilities,
 		switch (*p & X25_FAC_CLASS_MASK) {
 		case X25_FAC_CLASS_A:
 			if (len < 2)
-				return 0;
+				return -1;
 			switch (*p) {
 			case X25_FAC_REVERSE:
 				if((p[1] & 0x81) == 0x81) {
@@ -107,7 +117,7 @@ int x25_parse_facilities(struct sk_buff *skb, struct x25_facilities *facilities,
 			break;
 		case X25_FAC_CLASS_B:
 			if (len < 3)
-				return 0;
+				return -1;
 			switch (*p) {
 			case X25_FAC_PACKET_SIZE:
 				facilities->pacsize_in  = p[1];
@@ -130,7 +140,7 @@ int x25_parse_facilities(struct sk_buff *skb, struct x25_facilities *facilities,
 			break;
 		case X25_FAC_CLASS_C:
 			if (len < 4)
-				return 0;
+				return -1;
 			printk(KERN_DEBUG "X.25: unknown facility %02X, "
 			       "values %02X, %02X, %02X\n",
 			       p[0], p[1], p[2], p[3]);
@@ -139,18 +149,18 @@ int x25_parse_facilities(struct sk_buff *skb, struct x25_facilities *facilities,
 			break;
 		case X25_FAC_CLASS_D:
 			if (len < p[1] + 2)
-				return 0;
+				return -1;
 			switch (*p) {
 			case X25_FAC_CALLING_AE:
 				if (p[1] > X25_MAX_DTE_FACIL_LEN || p[1] <= 1)
-					return 0;
+					return -1;
 				dte_facs->calling_len = p[2];
 				memcpy(dte_facs->calling_ae, &p[3], p[1] - 1);
 				*vc_fac_mask |= X25_MASK_CALLING_AE;
 				break;
 			case X25_FAC_CALLED_AE:
 				if (p[1] > X25_MAX_DTE_FACIL_LEN || p[1] <= 1)
-					return 0;
+					return -1;
 				dte_facs->called_len = p[2];
 				memcpy(dte_facs->called_ae, &p[3], p[1] - 1);
 				*vc_fac_mask |= X25_MASK_CALLED_AE;

net/x25/x25_in.c

@@ -91,10 +91,10 @@ static int x25_state1_machine(struct sock *sk, struct sk_buff *skb, int frametyp
 {
 	struct x25_address source_addr, dest_addr;
 	int len;
+	struct x25_sock *x25 = x25_sk(sk);
 
 	switch (frametype) {
 		case X25_CALL_ACCEPTED: {
-			struct x25_sock *x25 = x25_sk(sk);
 
 			x25_stop_timer(sk);
 			x25->condition = 0x00;
@@ -113,14 +113,16 @@ static int x25_state1_machine(struct sock *sk, struct sk_buff *skb, int frametyp
 						&dest_addr);
 			if (len > 0)
 				skb_pull(skb, len);
+			else if (len < 0)
+				goto out_clear;
 
 			len = x25_parse_facilities(skb, &x25->facilities,
 						&x25->dte_facilities,
 						&x25->vc_facil_mask);
 			if (len > 0)
 				skb_pull(skb, len);
-			else
-				return -1;
+			else if (len < 0)
+				goto out_clear;
 			/*
 			 *	Copy any Call User Data.
 			 */
@@ -144,6 +146,12 @@ static int x25_state1_machine(struct sock *sk, struct sk_buff *skb, int frametyp
 	}
 
 	return 0;
+
+out_clear:
+	x25_write_internal(sk, X25_CLEAR_REQUEST);
+	x25->state = X25_STATE_2;
+	x25_start_t23timer(sk);
+	return 0;
 }
 
 /*