[PATCH net v3] net: axienet: safely drop oversized RX frames

[Can Ayberk Demir <ayberkdemir@gmail.com>]

From: Can Ayberk DEMIR <ayberkdemir@gmail.com>

In AXI Ethernet (axienet) driver, receiving an Ethernet frame larger
than the allocated skb buffer may cause memory corruption or kernel panic,
especially when the interface MTU is small and a jumbo frame is received.

Fixes: 8a3b7a252dca ("drivers/net/ethernet/xilinx: added Xilinx AXI Ethernet driver")

This bug was discovered during testing on a Kria K26 platform. When an
oversized frame is received and `skb_put()` is called without checking
the tailroom, the following kernel panic occurs:

  skb_panic+0x58/0x5c
  skb_put+0x90/0xb0
  axienet_rx_poll+0x130/0x4ec
  ...
  Kernel panic - not syncing: Oops - BUG: Fatal exception in interrupt

Signed-off-by: Can Ayberk DEMIR <ayberkdemir@gmail.com>
---
Changes in v3:
- Fixed 'ndev' undeclared error → replaced with 'lp->ndev'
- Added rx_dropped++ for statistics
- Added Fixes: tag

Changes in v2:
- This patch addresses style issues pointed out in v1.
---
 .../net/ethernet/xilinx/xilinx_axienet_main.c | 47 +++++++++++--------
 1 file changed, 28 insertions(+), 19 deletions(-)

diff --git a/drivers/net/ethernet/xilinx/xilinx_axienet_main.c b/drivers/net/ethernet/xilinx/xilinx_axienet_main.c
index 1b7a653c1f4e..7a12132e2b7c 100644
--- a/drivers/net/ethernet/xilinx/xilinx_axienet_main.c
+++ b/drivers/net/ethernet/xilinx/xilinx_axienet_main.c
@@ -1223,28 +1223,37 @@ static int axienet_rx_poll(struct napi_struct *napi, int budget)
 			dma_unmap_single(lp->dev, phys, lp->max_frm_size,
 					 DMA_FROM_DEVICE);
 
-			skb_put(skb, length);
-			skb->protocol = eth_type_trans(skb, lp->ndev);
-			/*skb_checksum_none_assert(skb);*/
-			skb->ip_summed = CHECKSUM_NONE;
-
-			/* if we're doing Rx csum offload, set it up */
-			if (lp->features & XAE_FEATURE_FULL_RX_CSUM) {
-				csumstatus = (cur_p->app2 &
-					      XAE_FULL_CSUM_STATUS_MASK) >> 3;
-				if (csumstatus == XAE_IP_TCP_CSUM_VALIDATED ||
-				    csumstatus == XAE_IP_UDP_CSUM_VALIDATED) {
-					skb->ip_summed = CHECKSUM_UNNECESSARY;
+			if (unlikely(length > skb_tailroom(skb))) {
+				netdev_warn(lp->ndev,
+					    "Dropping oversized RX frame (len=%u, tailroom=%u)\n",
+					    length, skb_tailroom(skb));
+				dev_kfree_skb(skb);
+				lp->ndev->stats.rx_dropped++;
+				skb = NULL;
+			} else {
+				skb_put(skb, length);
+				skb->protocol = eth_type_trans(skb, lp->ndev);
+				/*skb_checksum_none_assert(skb);*/
+				skb->ip_summed = CHECKSUM_NONE;
+
+				/* if we're doing Rx csum offload, set it up */
+				if (lp->features & XAE_FEATURE_FULL_RX_CSUM) {
+					csumstatus = (cur_p->app2 &
+							XAE_FULL_CSUM_STATUS_MASK) >> 3;
+					if (csumstatus == XAE_IP_TCP_CSUM_VALIDATED ||
+					    csumstatus == XAE_IP_UDP_CSUM_VALIDATED) {
+						skb->ip_summed = CHECKSUM_UNNECESSARY;
+					}
+				} else if (lp->features & XAE_FEATURE_PARTIAL_RX_CSUM) {
+					skb->csum = be32_to_cpu(cur_p->app3 & 0xFFFF);
+					skb->ip_summed = CHECKSUM_COMPLETE;
 				}
-			} else if (lp->features & XAE_FEATURE_PARTIAL_RX_CSUM) {
-				skb->csum = be32_to_cpu(cur_p->app3 & 0xFFFF);
-				skb->ip_summed = CHECKSUM_COMPLETE;
-			}
 
-			napi_gro_receive(napi, skb);
+				napi_gro_receive(napi, skb);
 
-			size += length;
-			packets++;
+				size += length;
+				packets++;
+			}
 		}
 
 		new_skb = napi_alloc_skb(napi, lp->max_frm_size);
-- 
2.39.5 (Apple Git-154)