octeon_ep: Add SKB allocation failures handling in __octep_oq_process_rx()

build_skb() returns NULL in case of a memory allocation failure so handle
it inside __octep_oq_process_rx() to avoid NULL pointer dereference.

__octep_oq_process_rx() is called during NAPI polling by the driver. If
skb allocation fails, keep on pulling packets out of the Rx DMA queue: we
shouldn't break the polling immediately and thus falsely indicate to the
octep_napi_poll() that the Rx pressure is going down. As there is no
associated skb in this case, don't process the packets and don't push them
up the network stack - they are skipped.

Helper function is implemented to unmmap/flush all the fragment buffers
used by the dropped packet. 'alloc_failures' counter is incremented to
mark the skb allocation error in driver statistics.

Found by Linux Verification Center (linuxtesting.org) with SVACE.

Fixes: 37d79d0 ("octeon_ep: add Tx/Rx processing and interrupt support")
Suggested-by: Paolo Abeni <[email protected]>
Signed-off-by: Aleksandr Mishin <[email protected]>
Reviewed-by: Jacob Keller <[email protected]>
Signed-off-by: Andrew Lunn <[email protected]>

Author: Aleksandr Mishin

drivers/net/ethernet/marvell/octeon_ep/octep_rx.c

@@ -360,6 +360,27 @@ static void octep_oq_next_pkt(struct octep_oq *oq,
 		*read_idx = 0;
 }
 
+/**
+ * octep_oq_drop_rx() - Free the resources associated with a packet.
+ *
+ * @oq: Octeon Rx queue data structure.
+ * @buff_info: Current packet buffer info.
+ * @read_idx: Current packet index in the ring.
+ * @desc_used: Current packet descriptor number.
+ *
+ */
+static void octep_oq_drop_rx(struct octep_oq *oq,
+			     struct octep_rx_buffer *buff_info,
+			     u32 *read_idx, u32 *desc_used)
+{
+	int data_len = buff_info->len - oq->max_single_buffer_size;
+
+	while (data_len > 0) {
+		octep_oq_next_pkt(oq, buff_info, read_idx, desc_used);
+		data_len -= oq->buffer_size;
+	};
+}
+
 /**
  * __octep_oq_process_rx() - Process hardware Rx queue and push to stack.
  *
@@ -419,6 +440,12 @@ static int __octep_oq_process_rx(struct octep_device *oct,
 		octep_oq_next_pkt(oq, buff_info, &read_idx, &desc_used);
 
 		skb = build_skb((void *)resp_hw, PAGE_SIZE);
+		if (!skb) {
+			octep_oq_drop_rx(oq, buff_info,
+					 &read_idx, &desc_used);
+			oq->stats.alloc_failures++;
+			continue;
+		}
 		skb_reserve(skb, data_offset);
 
 		rx_bytes += buff_info->len;