[bug report] net: axienet: Introduce dmaengine support

[Dan Carpenter <dan.carpenter@linaro.org>]

Hello Radhey Shyam Pandey,

Commit 6a91b846af85 ("net: axienet: Introduce dmaengine support")
from Nov 16, 2023 (linux-next), leads to the following Smatch static
checker warning:

	drivers/net/ethernet/xilinx/xilinx_axienet_main.c:1171 axienet_dma_rx_cb()
	error: 'app_metadata' dereferencing possible ERR_PTR()

drivers/net/ethernet/xilinx/xilinx_axienet_main.c
    1156 static void axienet_dma_rx_cb(void *data, const struct dmaengine_result *result)
    1157 {
    1158         struct skbuf_dma_descriptor *skbuf_dma;
    1159         size_t meta_len, meta_max_len, rx_len;
    1160         struct axienet_local *lp = data;
    1161         struct sk_buff *skb;
    1162         u32 *app_metadata;
    1163 
    1164         skbuf_dma = axienet_get_rx_desc(lp, lp->rx_ring_tail++);
    1165         skb = skbuf_dma->skb;
    1166         app_metadata = dmaengine_desc_get_metadata_ptr(skbuf_dma->desc, &meta_len,
                 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
No error checking.

    1167                                                        &meta_max_len);
    1168         dma_unmap_single(lp->dev, skbuf_dma->dma_address, lp->max_frm_size,
    1169                          DMA_FROM_DEVICE);
    1170         /* TODO: Derive app word index programmatically */
--> 1171         rx_len = (app_metadata[LEN_APP] & 0xFFFF);
                           ^^^^^^^^^^^^
Dereference.

    1172         skb_put(skb, rx_len);
    1173         skb->protocol = eth_type_trans(skb, lp->ndev);
    1174         skb->ip_summed = CHECKSUM_NONE;
    1175 
    1176         __netif_rx(skb);
    1177         u64_stats_update_begin(&lp->rx_stat_sync);
    1178         u64_stats_add(&lp->rx_packets, 1);
    1179         u64_stats_add(&lp->rx_bytes, rx_len);
    1180         u64_stats_update_end(&lp->rx_stat_sync);
    1181         axienet_rx_submit_desc(lp->ndev);
    1182         dma_async_issue_pending(lp->rx_chan);
    1183 }

regards,
dan carpenter