net: hv_netvsc: Fix a warning triggered by memcpy in rndis_filter

memcpy: detected field-spanning write (size 168) of single field "(void *)&request->response_msg + (sizeof(struct rndis_message) - sizeof(union rndis_message_container)) + sizeof(*req_id)" at drivers/net/hyperv/rndis_filter.c:338 (size 40)
RSP: 0018:ffffc90000144de0 EFLAGS: 00010282
RAX: 0000000000000000 RBX: ffff8881766b4000 RCX: 0000000000000000
RDX: 0000000000000102 RSI: 0000000000009ffb RDI: 00000000ffffffff
RBP: ffffc90000144e38 R08: 0000000000000000 R09: 00000000ffffdfff
R10: ffffc90000144c48 R11: ffffffff82f56ac8 R12: ffff8881766b403c
R13: 00000000000000a8 R14: ffff888100b75000 R15: ffff888179301d00
FS:  0000000000000000(0000) GS:ffff8884d6280000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 000055f8b024c418 CR3: 0000000176548001 CR4: 00000000003706e0
Call Trace:
 <IRQ>
 ? _raw_spin_unlock_irqrestore+0x27/0x50
 netvsc_poll+0x556/0x940 [hv_netvsc]
 __napi_poll+0x2e/0x170
 net_rx_action+0x299/0x2f0
 __do_softirq+0xed/0x2ef
 __irq_exit_rcu+0x9f/0x110
 irq_exit_rcu+0xe/0x20
 sysvec_hyperv_callback+0xb0/0xd0
 </IRQ>
 <TASK>
 asm_sysvec_hyperv_callback+0x1b/0x20
RIP: 0010:native_safe_halt+0xb/0x10

Fixes: A warning triggered when the response message len exceeds
the size of rndis_message. Inside the rndis_request structure
these fields are however followed by a RNDIS_EXT_LEN padding
so it is safe to use unsafe_memcpy.
Reviewed-by: Michael Kelley <mikelley@microsoft.com>
Signed-off-by: Cezar Bulinaru <cbulinaru@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/net/hyperv/rndis_filter.c

@@ -20,6 +20,7 @@
 #include <linux/vmalloc.h>
 #include <linux/rtnetlink.h>
 #include <linux/ucs2_string.h>
+#include <linux/string.h>
 
 #include "hyperv_net.h"
 #include "netvsc_trace.h"
@@ -335,9 +336,10 @@ static void rndis_filter_receive_response(struct net_device *ndev,
 		if (resp->msg_len <=
 		    sizeof(struct rndis_message) + RNDIS_EXT_LEN) {
 			memcpy(&request->response_msg, resp, RNDIS_HEADER_SIZE + sizeof(*req_id));
-			memcpy((void *)&request->response_msg + RNDIS_HEADER_SIZE + sizeof(*req_id),
+			unsafe_memcpy((void *)&request->response_msg + RNDIS_HEADER_SIZE + sizeof(*req_id),
 			       data + RNDIS_HEADER_SIZE + sizeof(*req_id),
-			       resp->msg_len - RNDIS_HEADER_SIZE - sizeof(*req_id));
+			       resp->msg_len - RNDIS_HEADER_SIZE - sizeof(*req_id),
+			       "request->response_msg is followed by a padding of RNDIS_EXT_LEN inside rndis_request");
 			if (request->request_msg.ndis_msg_type ==
 			    RNDIS_MSG_QUERY && request->request_msg.msg.
 			    query_req.oid == RNDIS_OID_GEN_MEDIA_CONNECT_STATUS)