net: hns3: fix use-after-free when doing self test

net: hns3: fix use-after-free when doing self test

Enable promisc mode of PF, set VF link state to enable, and
run iperf of the VF, then do self test of the PF. The self test
will fail with a low frequency, and may cause a use-after-free
problem.

[   87.142126] selftest:000004a0: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00  ................
[   87.159722] ==================================================================
[   87.174187] BUG: KASAN: use-after-free in hex_dump_to_buffer+0x140/0x608
[   87.187600] Read of size 1 at addr ffff003b22828000 by task ethtool/1186
[   87.201012]
[   87.203978] CPU: 7 PID: 1186 Comm: ethtool Not tainted 5.5.0-rc4-gfd51c473-dirty #4
[   87.219306] Hardware name: Huawei TaiShan 2280 V2/BC82AMDA, BIOS TA BIOS 2280-A CS V2.B160.01 01/15/2020
[   87.238292] Call trace:
[   87.243173]  dump_backtrace+0x0/0x280
[   87.250491]  show_stack+0x24/0x30
[   87.257114]  dump_stack+0xe8/0x140
[   87.263911]  print_address_description.isra.8+0x70/0x380
[   87.274538]  __kasan_report+0x12c/0x230
[   87.282203]  kasan_report+0xc/0x18
[   87.288999]  __asan_load1+0x60/0x68
[   87.295969]  hex_dump_to_buffer+0x140/0x608
[   87.304332]  print_hex_dump+0x140/0x1e0
[   87.312000]  hns3_lb_check_skb_data+0x168/0x170
[   87.321060]  hns3_clean_rx_ring+0xa94/0xfe0
[   87.329422]  hns3_self_test+0x708/0x8c0

The length of packet sent by the selftest process is only
128 + 14 bytes, and the min buffer size of a BD is 256 bytes,
and the receive process will make sure the packet sent by
the selftest process is in the linear part, so only check
the linear part in hns3_lb_check_skb_data().

So fix this use-after-free by using skb_headlen() to dump
skb->data instead of skb->len.

Fixes: c39c4d98dc65 ("net: hns3: Add mac loopback selftest support in hns3 driver")
Signed-off-by: Yonglong Liu <liuyonglong@huawei.com>
Signed-off-by: Huazhong Tan <tanhuazhong@huawei.com>
Signed-off-by: David S. Miller <davem@davemloft.net>