[PATCH v3 net-next] net: usb: smsc95xx: stop lying about skb->truesize

[PATCH v3 net-next] net: usb: smsc95xx: stop lying about skb->truesize

[Eric Dumazet]

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")

v3: also fix a sparse error ( https://lore.kernel.org/oe-kbuild-all/202405091310.KvncIecx-lkp@intel.com/ )
v2: leave the skb_trim() game because smsc95xx_rx_csum_offload()
    needs the csum part. (Jakub)
    While we are it, use get_unaligned() in smsc95xx_rx_csum_offload().

Fixes: 2f7ca802bdae ("net: Add SMSC LAN9500 USB2.0 10/100 ethernet adapter driver")
Signed-off-by: Eric Dumazet <edumazet@google.com>
Cc: Steve Glendinning <steve.glendinning@shawell.net>
Cc: UNGLinuxDriver@microchip.com
---
 drivers/net/usb/smsc95xx.c | 15 +++++++--------
 1 file changed, 7 insertions(+), 8 deletions(-)

diff --git a/drivers/net/usb/smsc95xx.c b/drivers/net/usb/smsc95xx.c
index 2fa46baa589e5e87e12e145fe46268bdaf9fc219..cbea246664795f27618908838b37384e8f3b67d0 100644
--- a/drivers/net/usb/smsc95xx.c
+++ b/drivers/net/usb/smsc95xx.c
@@ -1810,9 +1810,11 @@ static int smsc95xx_reset_resume(struct usb_interface *intf)
 
 static void smsc95xx_rx_csum_offload(struct sk_buff *skb)
 {
-	skb->csum = *(u16 *)(skb_tail_pointer(skb) - 2);
+	u16 *csum_ptr = (u16 *)(skb_tail_pointer(skb) - 2);
+
+	skb->csum = (__force __wsum)get_unaligned(csum_ptr);
 	skb->ip_summed = CHECKSUM_COMPLETE;
-	skb_trim(skb, skb->len - 2);
+	skb_trim(skb, skb->len - 2); /* remove csum */
 }
 
 static int smsc95xx_rx_fixup(struct usbnet *dev, struct sk_buff *skb)
@@ -1870,25 +1872,22 @@ static int smsc95xx_rx_fixup(struct usbnet *dev, struct sk_buff *skb)
 				if (dev->net->features & NETIF_F_RXCSUM)
 					smsc95xx_rx_csum_offload(skb);
 				skb_trim(skb, skb->len - 4); /* remove fcs */
-				skb->truesize = size + sizeof(struct sk_buff);
 
 				return 1;
 			}
 
-			ax_skb = skb_clone(skb, GFP_ATOMIC);
+			ax_skb = netdev_alloc_skb_ip_align(dev->net, size);
 			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);
+			memcpy(ax_skb->data, packet, size);
 
 			if (dev->net->features & NETIF_F_RXCSUM)
 				smsc95xx_rx_csum_offload(ax_skb);
 			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

Re: [PATCH v3 net-next] net: usb: smsc95xx: stop lying about skb->truesize

[Simon Horman]

On Thu, May 09, 2024 at 08:33:13AM +0000, Eric Dumazet wrote:
> 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")
> 
> v3: also fix a sparse error ( https://lore.kernel.org/oe-kbuild-all/202405091310.KvncIecx-lkp@intel.com/ )
> v2: leave the skb_trim() game because smsc95xx_rx_csum_offload()
>     needs the csum part. (Jakub)
>     While we are it, use get_unaligned() in smsc95xx_rx_csum_offload().
> 
> Fixes: 2f7ca802bdae ("net: Add SMSC LAN9500 USB2.0 10/100 ethernet adapter driver")
> Signed-off-by: Eric Dumazet <edumazet@google.com>
> Cc: Steve Glendinning <steve.glendinning@shawell.net>
> Cc: UNGLinuxDriver@microchip.com

Reviewed-by: Simon Horman <horms@kernel.org>

...

Re: [PATCH v3 net-next] net: usb: smsc95xx: stop lying about skb->truesize

[patchwork-bot+netdevbpf]

Hello:

This patch was applied to netdev/net-next.git (main)
by Jakub Kicinski <kuba@kernel.org>:

On Thu,  9 May 2024 08:33:13 +0000 you wrote:
> 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")
> 
> [...]

Here is the summary with links:
  - [v3,net-next] net: usb: smsc95xx: stop lying about skb->truesize
    https://git.kernel.org/netdev/net-next/c/d50729f1d60b

You are awesome, thank you!
-- 
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