When we receive a packet on a QMI device in raw IP mode, we should call skb_reset_mac_header() to ensure that skb->mac_header contains a valid offset in the packet. While it shouldn't really matter, the packets have no MAC header and the interface is configured as-such, it seems certain parts of the network stack expects a "good" value in skb->mac_header.
Without the skb_reset_mac_header() call added in this patch, for example shaping traffic (using tc) triggers the following oops on the first received packet: [ 303.642957] skbuff: skb_under_panic: text:8f137918 len:177 put:67 head:8e4b0f00 data:8e4b0eff tail:0x8e4b0fb0 end:0x8e4b1520 dev:wwan0 [ 303.655045] Kernel bug detected[#1]: [ 303.658622] CPU: 1 PID: 1002 Comm: logd Not tainted 4.9.58 #0 [ 303.664339] task: 8fdf05e0 task.stack: 8f15c000 [ 303.668844] $ 0 : 00000000 00000001 0000007a 00000000 [ 303.674062] $ 4 : 8149a2fc 8149a2fc 8149ce20 00000000 [ 303.679284] $ 8 : 00000030 3878303a 31623465 20303235 [ 303.684510] $12 : ded731e3 2626a277 00000000 03bd0000 [ 303.689747] $16 : 8ef62b40 00000043 8f137918 804db5fc [ 303.694978] $20 : 00000001 00000004 8fc13800 00000003 [ 303.700215] $24 : 00000001 8024ab10 [ 303.705442] $28 : 8f15c000 8fc19cf0 00000043 802cc920 [ 303.710664] Hi : 00000000 [ 303.713533] Lo : 74e58000 [ 303.716436] epc : 802cc920 skb_panic+0x58/0x5c [ 303.721046] ra : 802cc920 skb_panic+0x58/0x5c [ 303.725639] Status: 11007c03 KERNEL EXL IE [ 303.729823] Cause : 50800024 (ExcCode 09) [ 303.733817] PrId : 0001992f (MIPS 1004Kc) [ 303.737892] Modules linked in: rt2800pci rt2800mmio rt2800lib qcserial ppp_async option usb_wwan rt2x00pci rt2x00mmio rt2x00lib rndis_host qmi_wwan ppp_generic nf_nat_pptp nf_conntrack_pptp nf_conntrack_ipv6 mt76x2i Process logd (pid: 1002, threadinfo=8f15c000, task=8fdf05e0, tls=77b3eee4) [ 303.962509] Stack : 00000000 80408990 8f137918 000000b1 00000043 8e4b0f00 8e4b0eff 8e4b0fb0 [ 303.970871] 8e4b1520 8fec1800 00000043 802cd2a4 6e000045 00000043 00000000 8ef62000 [ 303.979219] 8eef5d00 8ef62b40 8fea7300 8f137918 00000000 00000000 0002bb01 793e5664 [ 303.987568] 8ef08884 00000001 8fea7300 00000002 8fc19e80 8eef5d00 00000006 00000003 [ 303.995934] 00000000 8030ba90 00000003 77ab3fd0 8149dc80 8004d1bc 8f15c000 8f383700 [ 304.004324] ... [ 304.006767] Call Trace: [ 304.009241] [<802cc920>] skb_panic+0x58/0x5c [ 304.013504] [<802cd2a4>] skb_push+0x78/0x90 [ 304.017783] [<8f137918>] 0x8f137918 [ 304.021269] Code: 00602825 0c02a3b4 24842888 <000c000d> 8c870060 8c8200a0 0007382b 00070336 8c88005c [ 304.031034] [ 304.032805] ---[ end trace b778c482b3f0bda9 ]--- [ 304.041384] Kernel panic - not syncing: Fatal exception in interrupt [ 304.051975] Rebooting in 3 seconds.. While the oops is for a 4.9-kernel, I was able to trigger the same oops with net-next as of yesterday. Signed-off-by: Kristian Evensen <kristian.even...@gmail.com> --- drivers/net/usb/qmi_wwan.c | 1 + 1 file changed, 1 insertion(+) diff --git a/drivers/net/usb/qmi_wwan.c b/drivers/net/usb/qmi_wwan.c index db7279d5b250..5b22645c7c8c 100644 --- a/drivers/net/usb/qmi_wwan.c +++ b/drivers/net/usb/qmi_wwan.c @@ -499,6 +499,7 @@ static int qmi_wwan_rx_fixup(struct usbnet *dev, struct sk_buff *skb) return 1; } if (rawip) { + skb_reset_mac_header(skb); skb->dev = dev->net; /* normally set by eth_type_trans */ skb->protocol = proto; return 1; -- 2.11.0