[PATCH net] net: usb: ax88179_178a: stop lying about skb->truesize

[PATCH net] net: usb: ax88179_178a: 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 overide.

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")

Fixes: f8ebb3ac881b ("net: usb: ax88179_178a: Fix packet receiving")
Reported-by: shironeko <shironeko@tesaguri.club>
Closes: https://lore.kernel.org/netdev/c110f41a0d2776b525930f213ca9715c@tesaguri.club/
Signed-off-by: Eric Dumazet <edumazet@google.com>
Cc: Jose Alonso <joalonsof@gmail.com>
Cc: linux-usb@vger.kernel.org
---
 drivers/net/usb/ax88179_178a.c | 11 +++--------
 1 file changed, 3 insertions(+), 8 deletions(-)

diff --git a/drivers/net/usb/ax88179_178a.c b/drivers/net/usb/ax88179_178a.c
index 752f821a19901f313a1aca51fe332539ce82385b..df9d767cb524241848c744504d6e2999efc42ed5 100644
--- a/drivers/net/usb/ax88179_178a.c
+++ b/drivers/net/usb/ax88179_178a.c
@@ -1456,21 +1456,16 @@ static int ax88179_rx_fixup(struct usbnet *dev, struct sk_buff *skb)
 			/* Skip IP alignment pseudo header */
 			skb_pull(skb, 2);
 
-			skb->truesize = SKB_TRUESIZE(pkt_len_plus_padd);
 			ax88179_rx_checksum(skb, pkt_hdr);
 			return 1;
 		}
 
-		ax_skb = skb_clone(skb, GFP_ATOMIC);
+		ax_skb = netdev_alloc_skb_ip_align(dev->net, pkt_len);
 		if (!ax_skb)
 			return 0;
-		skb_trim(ax_skb, pkt_len);
+		skb_put(ax_skb, pkt_len);
+		memcpy(ax_skb->data, skb->data + 2, pkt_len);
 
-		/* Skip IP alignment pseudo header */
-		skb_pull(ax_skb, 2);
-
-		skb->truesize = pkt_len_plus_padd +
-				SKB_DATA_ALIGN(sizeof(struct sk_buff));
 		ax88179_rx_checksum(ax_skb, pkt_hdr);
 		usbnet_skb_return(dev, ax_skb);
 
-- 
2.44.0.769.g3c40516874-goog

Re: [PATCH net] net: usb: ax88179_178a: stop lying about skb->truesize

[Simon Horman]

On Sun, Apr 21, 2024 at 07:38:28PM +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 overide.
> 
> 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")
> 
> Fixes: f8ebb3ac881b ("net: usb: ax88179_178a: Fix packet receiving")
> Reported-by: shironeko <shironeko@tesaguri.club>
> Closes: https://lore.kernel.org/netdev/c110f41a0d2776b525930f213ca9715c@tesaguri.club/
> Signed-off-by: Eric Dumazet <edumazet@google.com>
> Cc: Jose Alonso <joalonsof@gmail.com>
> Cc: linux-usb@vger.kernel.org

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

Re: [PATCH net] net: usb: ax88179_178a: stop lying about skb->truesize

[patchwork-bot+netdevbpf]

Hello:

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

On Sun, 21 Apr 2024 19:38:28 +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 overide.
> 
> 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")
> 
> [...]

Here is the summary with links:
  - [net] net: usb: ax88179_178a: stop lying about skb->truesize
    https://git.kernel.org/netdev/net/c/4ce62d5b2f7a

You are awesome, thank you!
-- 
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