rxrpc: Fix handling of last subpacket of jumbo packet

When rxrpc_recvmsg_data() sets the return value to 1 because it's drained
all the data for the last packet, it checks the last-packet flag on the
whole packet - but this is wrong, since the last-packet flag is only set on
the final subpacket of the last jumbo packet. This means that a call that
receives its last packet in a jumbo packet won't complete properly.

Fix this by having rxrpc_locate_data() determine the last-packet state of
the subpacket it's looking at and passing that back to the caller rather
than having the caller look in the packet header. The caller then needs to
cache this in the rxrpc_call struct as rxrpc_locate_data() isn't then
called again for this packet.

Fixes: 248f219cb8bc ("rxrpc: Rewrite the data and ack handling code")
Fixes: e2de6c404898 ("rxrpc: Use info in skbuff instead of reparsing a jumbo packet")
Signed-off-by: David Howells <[e-mail]>
Signed-off-by: David S. Miller <[e-mail]>

net/rxrpc/ar-internal.h

···
 	int			debug_id;	/* debug ID for printks */
 	unsigned short		rx_pkt_offset;	/* Current recvmsg packet offset */
 	unsigned short		rx_pkt_len;	/* Current recvmsg packet len */
+	bool			rx_pkt_last;	/* Current recvmsg packet is last */
 
 	/* Rx/Tx circular buffer, depending on phase.
 	 *

net/rxrpc/recvmsg.c

···
  */
 static int rxrpc_locate_data(struct rxrpc_call *call, struct sk_buff *skb,
 			     u8 *_annotation,
-			     unsigned int *_offset, unsigned int *_len)
+			     unsigned int *_offset, unsigned int *_len,
+			     bool *_last)
 {
 	struct rxrpc_skb_priv *sp = rxrpc_skb(skb);
 	unsigned int offset = sizeof(struct rxrpc_wire_header);
 	unsigned int len;
+	bool last = false;
 	int ret;
 	u8 annotation = *_annotation;
 	u8 subpacket = annotation & RXRPC_RX_ANNO_SUBPACKET;
···
 	len = skb->len - offset;
 	if (subpacket < sp->nr_subpackets - 1)
 		len = RXRPC_JUMBO_DATALEN;
+	else if (sp->rx_flags & RXRPC_SKB_INCL_LAST)
+		last = true;
 
 	if (!(annotation & RXRPC_RX_ANNO_VERIFIED)) {
 		ret = rxrpc_verify_packet(call, skb, annotation, offset, len);
···
 
 	*_offset = offset;
 	*_len = len;
+	*_last = last;
 	call->security->locate_data(call, skb, _offset, _len);
 	return 0;
 }
···
 	rxrpc_serial_t serial;
 	rxrpc_seq_t hard_ack, top, seq;
 	size_t remain;
-	bool last;
+	bool rx_pkt_last;
 	unsigned int rx_pkt_offset, rx_pkt_len;
 	int ix, copy, ret = -EAGAIN, ret2;
 
···
 
 	rx_pkt_offset = call->rx_pkt_offset;
 	rx_pkt_len = call->rx_pkt_len;
+	rx_pkt_last = call->rx_pkt_last;
 
 	if (call->state >= RXRPC_CALL_SERVER_ACK_REQUEST) {
 		seq = call->rx_hard_ack;
···
 	/* Barriers against rxrpc_input_data(). */
 	hard_ack = call->rx_hard_ack;
 	seq = hard_ack + 1;
+
 	while (top = smp_load_acquire(&call->rx_top),
 	       before_eq(seq, top)
 	       ) {
···
 		if (rx_pkt_offset == 0) {
 			ret2 = rxrpc_locate_data(call, skb,
 						 &call->rxtx_annotations[ix],
-						 &rx_pkt_offset, &rx_pkt_len);
+						 &rx_pkt_offset, &rx_pkt_len,
+						 &rx_pkt_last);
 			trace_rxrpc_recvmsg(call, rxrpc_recvmsg_next, seq,
 					    rx_pkt_offset, rx_pkt_len, ret2);
 			if (ret2 < 0) {
···
 		}
 
 		/* The whole packet has been transferred. */
-		last = sp->hdr.flags & RXRPC_LAST_PACKET;
 		if (!(flags & MSG_PEEK))
 			rxrpc_rotate_rx_window(call);
 		rx_pkt_offset = 0;
 		rx_pkt_len = 0;
 
-		if (last) {
+		if (rx_pkt_last) {
 			ASSERTCMP(seq, ==, READ_ONCE(call->rx_top));
 			ret = 1;
 			goto out;
···
 	if (!(flags & MSG_PEEK)) {
 		call->rx_pkt_offset = rx_pkt_offset;
 		call->rx_pkt_len = rx_pkt_len;
+		call->rx_pkt_last = rx_pkt_last;
 	}
 done:
 	trace_rxrpc_recvmsg(call, rxrpc_recvmsg_data_return, seq,