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@google.com>
Cc: Steve Glendinning <steve.glendinning@shawell.net>
Link: https://lore.kernel.org/r/20240506142358.3657918-1-edumazet@google.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

diff --git a/drivers/net/usb/smsc75xx.c b/drivers/net/usb/smsc75xx.c
index 78ad2da3ee29b225f41eddc90b08d43257d01e8f..0726e18bee6fcf3cbe4b3d2006d40cc2f781b64c 100644 (file)
--- 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);
                }