x25: Handle undersized/fragmented skbs

There are multiple locations in the X.25 packet layer where a skb is
assumed to be of at least a certain size and that all its data is
currently available at skb->data. These assumptions are not checked,
hence buffer overreads may occur. Use pskb_may_pull to check these
minimal size assumptions and ensure that data is available at skb->data
when necessary, as well as use skb_copy_bits where needed.

Signed-off-by: Matthew Daley <[e-mail]>
Cc: Eric Dumazet <[e-mail]>
Cc: Andrew Hendry <[e-mail]>
Cc: stable <[e-mail]>
Acked-by: Andrew Hendry <[e-mail]>
Signed-off-by: David S. Miller <[e-mail]>

net/x25/af_x25.c

···
 	int needed;
 	int rc;
 
-	if (skb->len < 1) {
+	if (!pskb_may_pull(skb, 1)) {
 		/* packet has no address block */
 		rc = 0;
 		goto empty;
···
 	len = *skb->data;
 	needed = 1 + (len >> 4) + (len & 0x0f);
 
-	if (skb->len < needed) {
+	if (!pskb_may_pull(skb, needed)) {
 		/* packet is too short to hold the addresses it claims
 		   to hold */
 		rc = -1;
···
 	 *
 	 *	Facilities length is mandatory in call request packets
 	 */
-	if (skb->len < 1)
+	if (!pskb_may_pull(skb, 1))
 		goto out_clear_request;
 	len = skb->data[0] + 1;
-	if (skb->len < len)
+	if (!pskb_may_pull(skb, len))
 		goto out_clear_request;
 	skb_pull(skb,len);
 
···
 	 *	Ensure that the amount of call user data is valid.
 	 */
 	if (skb->len > X25_MAX_CUD_LEN)
+		goto out_clear_request;
+
+	/*
+	 *	Get all the call user data so it can be used in
+	 *	x25_find_listener and skb_copy_from_linear_data up ahead.
+	 */
+	if (!pskb_may_pull(skb, skb->len))
 		goto out_clear_request;
 
 	/*
···
 	 *	byte of the user data is the logical value of the Q Bit.
 	 */
 	if (test_bit(X25_Q_BIT_FLAG, &x25->flags)) {
+		if (!pskb_may_pull(skb, 1))
+			goto out_kfree_skb;
+
 		qbit = skb->data[0];
 		skb_pull(skb, 1);
 	}
···
 	struct x25_sock *x25 = x25_sk(sk);
 	struct sockaddr_x25 *sx25 = (struct sockaddr_x25 *)msg->msg_name;
 	size_t copied;
-	int qbit;
+	int qbit, header_len = x25->neighbour->extended ?
+		X25_EXT_MIN_LEN : X25_STD_MIN_LEN;
+
 	struct sk_buff *skb;
 	unsigned char *asmptr;
 	int rc = -ENOTCONN;
···
 			goto out;
 
 		skb = skb_dequeue(&x25->interrupt_in_queue);
+
+		if (!pskb_may_pull(skb, X25_STD_MIN_LEN))
+			goto out_free_dgram;
 
 		skb_pull(skb, X25_STD_MIN_LEN);
 
···
 		if (!skb)
 			goto out;
 
+		if (!pskb_may_pull(skb, header_len))
+			goto out_free_dgram;
+
 		qbit = (skb->data[0] & X25_Q_BIT) == X25_Q_BIT;
 
-		skb_pull(skb, x25->neighbour->extended ?
-				X25_EXT_MIN_LEN : X25_STD_MIN_LEN);
+		skb_pull(skb, header_len);
 
 		if (test_bit(X25_Q_BIT_FLAG, &x25->flags)) {
 			asmptr  = skb_push(skb, 1);

net/x25/x25_dev.c

···
 	unsigned short frametype;
 	unsigned int lci;
 
+	if (!pskb_may_pull(skb, X25_STD_MIN_LEN))
+		return 0;
+
 	frametype = skb->data[2];
 	lci = ((skb->data[0] << 8) & 0xF00) + ((skb->data[1] << 0) & 0x0FF);
 
···
 		printk(KERN_DEBUG "X.25: unknown neighbour - %s\n", dev->name);
 		goto drop;
 	}
+
+	if (!pskb_may_pull(skb, 1))
+		return 0;
 
 	switch (skb->data[0]) {
 

net/x25/x25_facilities.c

···
 int x25_parse_facilities(struct sk_buff *skb, struct x25_facilities *facilities,
 		struct x25_dte_facilities *dte_facs, unsigned long *vc_fac_mask)
 {
-	unsigned char *p = skb->data;
+	unsigned char *p;
 	unsigned int len;
 
 	*vc_fac_mask = 0;
···
 	memset(dte_facs->called_ae, '\0', sizeof(dte_facs->called_ae));
 	memset(dte_facs->calling_ae, '\0', sizeof(dte_facs->calling_ae));
 
-	if (skb->len < 1)
+	if (!pskb_may_pull(skb, 1))
 		return 0;
 
-	len = *p++;
+	len = skb->data[0];
 
-	if (len >= skb->len)
+	if (!pskb_may_pull(skb, 1 + len))
 		return -1;
+
+	p = skb->data + 1;
 
 	while (len > 0) {
 		switch (*p & X25_FAC_CLASS_MASK) {

net/x25/x25_in.c

···
 		/*
 		 *	Parse the data in the frame.
 		 */
+		if (!pskb_may_pull(skb, X25_STD_MIN_LEN))
+			goto out_clear;
 		skb_pull(skb, X25_STD_MIN_LEN);
 
 		len = x25_parse_address_block(skb, &source_addr,
···
 			if (skb->len > X25_MAX_CUD_LEN)
 				goto out_clear;
 
-			skb_copy_from_linear_data(skb,
-						  x25->calluserdata.cuddata,
-						  skb->len);
+			skb_copy_bits(skb, 0, x25->calluserdata.cuddata,
+				skb->len);
 			x25->calluserdata.cudlength = skb->len;
 		}
 		if (!sock_flag(sk, SOCK_DEAD))
···
 		break;
 	}
 	case X25_CLEAR_REQUEST:
+		if (!pskb_may_pull(skb, X25_STD_MIN_LEN + 2))
+			goto out_clear;
+
 		x25_write_internal(sk, X25_CLEAR_CONFIRMATION);
 		x25_disconnect(sk, ECONNREFUSED, skb->data[3], skb->data[4]);
 		break;
···
 	switch (frametype) {
 
 		case X25_CLEAR_REQUEST:
+			if (!pskb_may_pull(skb, X25_STD_MIN_LEN + 2))
+				goto out_clear;
+
 			x25_write_internal(sk, X25_CLEAR_CONFIRMATION);
 			x25_disconnect(sk, 0, skb->data[3], skb->data[4]);
 			break;
···
 			break;
 	}
 
+	return 0;
+
+out_clear:
+	x25_write_internal(sk, X25_CLEAR_REQUEST);
+	x25_start_t23timer(sk);
 	return 0;
 }
 
···
 			break;
 
 		case X25_CLEAR_REQUEST:
+			if (!pskb_may_pull(skb, X25_STD_MIN_LEN + 2))
+				goto out_clear;
+
 			x25_write_internal(sk, X25_CLEAR_CONFIRMATION);
 			x25_disconnect(sk, 0, skb->data[3], skb->data[4]);
 			break;
···
 	}
 
 	return queued;
+
+out_clear:
+	x25_write_internal(sk, X25_CLEAR_REQUEST);
+	x25->state = X25_STATE_2;
+	x25_start_t23timer(sk);
+	return 0;
 }
 
 /*
···
  */
 static int x25_state4_machine(struct sock *sk, struct sk_buff *skb, int frametype)
 {
+	struct x25_sock *x25 = x25_sk(sk);
+
 	switch (frametype) {
 
 		case X25_RESET_REQUEST:
 			x25_write_internal(sk, X25_RESET_CONFIRMATION);
 		case X25_RESET_CONFIRMATION: {
-			struct x25_sock *x25 = x25_sk(sk);
-
 			x25_stop_timer(sk);
 			x25->condition = 0x00;
 			x25->va        = 0;
···
 			break;
 		}
 		case X25_CLEAR_REQUEST:
+			if (!pskb_may_pull(skb, X25_STD_MIN_LEN + 2))
+				goto out_clear;
+
 			x25_write_internal(sk, X25_CLEAR_CONFIRMATION);
 			x25_disconnect(sk, 0, skb->data[3], skb->data[4]);
 			break;
···
 			break;
 	}
 
+	return 0;
+
+out_clear:
+	x25_write_internal(sk, X25_CLEAR_REQUEST);
+	x25->state = X25_STATE_2;
+	x25_start_t23timer(sk);
 	return 0;
 }
 

net/x25/x25_link.c

···
 		break;
 
 	case X25_DIAGNOSTIC:
+		if (!pskb_may_pull(skb, X25_STD_MIN_LEN + 4))
+			break;
+
 		printk(KERN_WARNING "x25: diagnostic #%d - %02X %02X %02X\n",
 		       skb->data[3], skb->data[4],
 		       skb->data[5], skb->data[6]);

net/x25/x25_subr.c

···
 	       int *d, int *m)
 {
 	struct x25_sock *x25 = x25_sk(sk);
-	unsigned char *frame = skb->data;
+	unsigned char *frame;
+
+	if (!pskb_may_pull(skb, X25_STD_MIN_LEN))
+		return X25_ILLEGAL;
+	frame = skb->data;
 
 	*ns = *nr = *q = *d = *m = 0;
 
···
 		if (frame[2] == X25_RR  ||
 		    frame[2] == X25_RNR ||
 		    frame[2] == X25_REJ) {
+			if (!pskb_may_pull(skb, X25_EXT_MIN_LEN))
+				return X25_ILLEGAL;
+			frame = skb->data;
+
 			*nr = (frame[3] >> 1) & 0x7F;
 			return frame[2];
 		}
···
 
 	if (x25->neighbour->extended) {
 		if ((frame[2] & 0x01) == X25_DATA) {
+			if (!pskb_may_pull(skb, X25_EXT_MIN_LEN))
+				return X25_ILLEGAL;
+			frame = skb->data;
+
 			*q  = (frame[0] & X25_Q_BIT) == X25_Q_BIT;
 			*d  = (frame[0] & X25_D_BIT) == X25_D_BIT;
 			*m  = (frame[3] & X25_EXT_M_BIT) == X25_EXT_M_BIT;