[PATCH 4.9 30/48] net: amd-xgbe: Fix skb data length underflow

[Greg Kroah-Hartman <gregkh@linuxfoundation.org>]

From: Shyam Sundar S K <Shyam-sundar.S-k@amd.com>

commit 5aac9108a180fc06e28d4e7fb00247ce603b72ee upstream.

There will be BUG_ON() triggered in include/linux/skbuff.h leading to
intermittent kernel panic, when the skb length underflow is detected.

Fix this by dropping the packet if such length underflows are seen
because of inconsistencies in the hardware descriptors.

Fixes: 622c36f143fc ("amd-xgbe: Fix jumbo MTU processing on newer hardware")
Suggested-by: Tom Lendacky <thomas.lendacky@amd.com>
Signed-off-by: Shyam Sundar S K <Shyam-sundar.S-k@amd.com>
Acked-by: Tom Lendacky <thomas.lendacky@amd.com>
Link: https://lore.kernel.org/r/20220127092003.2812745-1-Shyam-sundar.S-k@amd.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
 drivers/net/ethernet/amd/xgbe/xgbe-drv.c |   12 +++++++++++-
 1 file changed, 11 insertions(+), 1 deletion(-)

--- a/drivers/net/ethernet/amd/xgbe/xgbe-drv.c
+++ b/drivers/net/ethernet/amd/xgbe/xgbe-drv.c
@@ -1968,6 +1968,14 @@ read_again:
 			buf2_len = xgbe_rx_buf2_len(rdata, packet, len);
 			len += buf2_len;
 
+			if (buf2_len > rdata->rx.buf.dma_len) {
+				/* Hardware inconsistency within the descriptors
+				 * that has resulted in a length underflow.
+				 */
+				error = 1;
+				goto skip_data;
+			}
+
 			if (!skb) {
 				skb = xgbe_create_skb(pdata, napi, rdata,
 						      buf1_len);
@@ -1997,8 +2005,10 @@ skip_data:
 		if (!last || context_next)
 			goto read_again;
 
-		if (!skb)
+		if (!skb || error) {
+			dev_kfree_skb(skb);
 			goto next_packet;
+		}
 
 		/* Be sure we don't exceed the configured MTU */
 		max_len = netdev->mtu + ETH_HLEN;