[PATCH AUTOSEL 4.9 02/13] net: usb: ax88179_178a: fix packet alignment padding

Sasha Levin
2020-07-02T01:28:28Z

From: Jeremy Kerr <jk@ozlabs.org>

[ Upstream commit e869e7a17798d85829fa7d4f9bbe1eebd4b2d3f6 ]

Using a AX88179 device (0b95:1790), I see two bytes of appended data on
every RX packet. For example, this 48-byte ping, using 0xff as a
payload byte:

04:20:22.528472 IP 192.168.1.1 > 192.168.1.2: ICMP echo request, id 2447, seq 1, length 64
0x0000: 000a cd35 ea50 000a cd35 ea4f 0800 4500
0x0010: 0054 c116 4000 4001 f63e c0a8 0101 c0a8
0x0020: 0102 0800 b633 098f 0001 87ea cd5e 0000
0x0030: 0000 dcf2 0600 0000 0000 ffff ffff ffff
0x0040: ffff ffff ffff ffff ffff ffff ffff ffff
0x0050: ffff ffff ffff ffff ffff ffff ffff ffff
0x0060: ffff 961f

Those last two bytes - 96 1f - aren't part of the original packet.

In the ax88179 RX path, the usbnet rx_fixup function trims a 2-byte
'alignment pseudo header' from the start of the packet, and sets the
length from a per-packet field populated by hardware. It looks like that
length field *includes* the 2-byte header; the current driver assumes
that it's excluded.

This change trims the 2-byte alignment header after we've set the packet
length, so the resulting packet length is correct. While we're moving
the comment around, this also fixes the spelling of 'pseudo'.

Signed-off-by: Jeremy Kerr <jk@ozlabs.org>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
drivers/net/usb/ax88179_178a.c | 11 ++++++-----
1 file changed, 6 insertions(+), 5 deletions(-)

diff --git a/drivers/net/usb/ax88179_178a.c b/drivers/net/usb/ax88179_178a.c
index 559af8e6ad90f..0434ecf677122 100644
--- a/drivers/net/usb/ax88179_178a.c
+++ b/drivers/net/usb/ax88179_178a.c
@@ -1396,10 +1396,10 @@ static int ax88179_rx_fixup(struct usbnet *dev, struct sk_buff *skb)
}

if (pkt_cnt == 0) {
- /* Skip IP alignment psudo header */
- skb_pull(skb, 2);
skb->len = pkt_len;
- skb_set_tail_pointer(skb, pkt_len);
+ /* Skip IP alignment pseudo header */
+ skb_pull(skb, 2);
+ skb_set_tail_pointer(skb, skb->len);
skb->truesize = pkt_len + sizeof(struct sk_buff);
ax88179_rx_checksum(skb, pkt_hdr);
return 1;
@@ -1408,8 +1408,9 @@ static int ax88179_rx_fixup(struct usbnet *dev, struct sk_buff *skb)
ax_skb = skb_clone(skb, GFP_ATOMIC);
if (ax_skb) {
ax_skb->len = pkt_len;
- ax_skb->data = skb->data + 2;
- skb_set_tail_pointer(ax_skb, pkt_len);
+ /* Skip IP alignment pseudo header */
+ skb_pull(ax_skb, 2);
+ skb_set_tail_pointer(ax_skb, ax_skb->len);
ax_skb->truesize = pkt_len + sizeof(struct sk_buff);
ax88179_rx_checksum(ax_skb, pkt_hdr);
usbnet_skb_return(dev, ax_skb);
--
2.25.1