netdev - [PATCH net-next] net: usb: smsc75xx: stop lying about skb->truesize

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Message-ID: <20240506142358.3657918-1-edumazet@google.com>
Date: Mon,  6 May 2024 14:23:58 +0000
From: Eric Dumazet <edumazet@...gle.com>
To: "David S . Miller" <davem@...emloft.net>, Jakub Kicinski <kuba@...nel.org>, 
	Paolo Abeni <pabeni@...hat.com>
Cc: netdev@...r.kernel.org, eric.dumazet@...il.com, 
	Eric Dumazet <edumazet@...gle.com>, Steve Glendinning <steve.glendinning@...well.net>
Subject: [PATCH net-next] net: usb: smsc75xx: stop lying about skb->truesize

Some usb drivers try to set small skb->truesize and break
core networking stacks.

In this patch, I removed one of the skb->truesize override.

I also replaced one skb_clone() by an allocation of a fresh
and small skb, to get minimally sized skbs, like we did
in commit 1e2c61172342 ("net: cdc_ncm: reduce skb truesize
in rx path") and 4ce62d5b2f7a ("net: usb: ax88179_178a:
stop lying about skb->truesize")

Signed-off-by: Eric Dumazet <edumazet@...gle.com>
Cc: Steve Glendinning <steve.glendinning@...well.net>
---
 drivers/net/usb/smsc75xx.c | 12 ++++--------
 1 file changed, 4 insertions(+), 8 deletions(-)

diff --git a/drivers/net/usb/smsc75xx.c b/drivers/net/usb/smsc75xx.c
index 78ad2da3ee29b225f41eddc90b08d43257d01e8f..0726e18bee6fcf3cbe4b3d2006d40cc2f781b64c 100644
--- a/drivers/net/usb/smsc75xx.c
+++ b/drivers/net/usb/smsc75xx.c
@@ -2234,27 +2234,23 @@ static int smsc75xx_rx_fixup(struct usbnet *dev, struct sk_buff *skb)
 					rx_cmd_b);
 
 				skb_trim(skb, skb->len - 4); /* remove fcs */
-				skb->truesize = size + sizeof(struct sk_buff);
 
 				return 1;
 			}
 
-			ax_skb = skb_clone(skb, GFP_ATOMIC);
+			/* Use "size - 4" to remove fcs */
+			ax_skb = netdev_alloc_skb_ip_align(dev->net, size - 4);
 			if (unlikely(!ax_skb)) {
 				netdev_warn(dev->net, "Error allocating skb\n");
 				return 0;
 			}
 
-			ax_skb->len = size;
-			ax_skb->data = packet;
-			skb_set_tail_pointer(ax_skb, size);
+			skb_put(ax_skb, size - 4);
+			memcpy(ax_skb->data, packet, size - 4);
 
 			smsc75xx_rx_csum_offload(dev, ax_skb, rx_cmd_a,
 				rx_cmd_b);
 
-			skb_trim(ax_skb, ax_skb->len - 4); /* remove fcs */
-			ax_skb->truesize = size + sizeof(struct sk_buff);
-
 			usbnet_skb_return(dev, ax_skb);
 		}
 
-- 
2.45.0.rc1.225.g2a3ae87e7f-goog