lan78xx.c:rx_submit() allocates space for frame-to-be-received with
netdev_alloc_skb_ip_align(), which misalign start of buffer by 2 bytes
in expectation that frame will start from 14-byte ethernet header, then
ip header; if start of buffer misaligned by 2 bytes, ip header will be
16-byte aligned.
Unfortunately, usb frame that is sent by lan78xx starts with another
10-byte header (lan78xx_rx(): rx_cmd_a/rx_cmd_b/rx_cmd_c), *then*
follows ethernet header, and *then* ip header (which ends up being
misaligned).
This issue was observed on arm platform (where misaligned 32-bit word
access triggers exception and leaves traces in /proc/cpu/alignment, see
https://github.com/raspberrypi/linux/issues/2599 ; for me, about any
ipv6 traffic that hits machine - `ping -I eth0 ip6-allnodes`, tcp/udp
packets, etc triggered increase in this counter, with
ip6_datagram_recv_common_ctl, icmpv6_echo_reply, etc as culprit).
If we just allocate skb data without any misalignment tricks, ip header
will end up and at offset 24 (8-byte aligned).
Patch attached; runtime-tested with raspbian fork of stable/4.14.y
[4.14.92] on Raspberry pi 3B+ (it is slightly different from mainline,
but patch should not have any conflicts, all affected code is pretty same).
P.S. I'm not subscribed, please CC me on reply.
>From 2bd6b0a11e222be2df97da948924c71bf13d7192 Mon Sep 17 00:00:00 2001
From: "Yuriy M. Kaminskiy" <yum...@gmail.com>
Date: Mon, 21 Jan 2019 02:51:24 +0300
Subject: [PATCH] lan78xx: fix ip header misalignment
As lan78xx prepends 10-byte header before ether_hdr, skb->data
misalignment trick by netdev_alloc_skb_ip_align() made things
worse (ip_hdr becomes always misaligned).
See https://github.com/raspberrypi/linux/issues/2599
---
drivers/net/usb/lan78xx.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/drivers/net/usb/lan78xx.c b/drivers/net/usb/lan78xx.c
index 9b782cdf8..d64b0d3b8 100644
--- a/drivers/net/usb/lan78xx.c
+++ b/drivers/net/usb/lan78xx.c
@@ -3143,7 +3143,7 @@ static int rx_submit(struct lan78xx_net *dev, struct urb *urb, gfp_t flags)
size_t size = dev->rx_urb_size;
int ret = 0;
- skb = netdev_alloc_skb_ip_align(dev->net, size);
+ skb = netdev_alloc_skb(dev->net, size);
if (!skb) {
usb_free_urb(urb);
return -ENOMEM;
--
2.11.0
