net: ping: Fix stack buffer overflow in ping_common_sendmsg()

In ping_common_sendmsg(), when len < icmph_len, memcpy_fromiovec()
will access invalid memory because msg->msg_iov only has 1 element
and memcpy_fromiovec() attempts to increment it. KASAN report:

BUG: KASAN: stack-out-of-bounds in memcpy_fromiovec+0x60/0x114 at addr ffffffc071077da0
Read of size 8 by task trinity-c2/9623
page:ffffffbe034b9a08 count:0 mapcount:0 mapping:          (null) index:0x0
flags: 0x0()
page dumped because: kasan: bad access detected
CPU: 0 PID: 9623 Comm: trinity-c2 Tainted: G    BU         3.18.0-dirty #15
Hardware name: Google Tegra210 Smaug Rev 1,3+ (DT)
Call trace:
[<ffffffc000209c98>] dump_backtrace+0x0/0x1ac arch/arm64/kernel/traps.c:90
[<ffffffc000209e54>] show_stack+0x10/0x1c arch/arm64/kernel/traps.c:171
[<     inline     >] __dump_stack lib/dump_stack.c:15
[<ffffffc000f18dc4>] dump_stack+0x7c/0xd0 lib/dump_stack.c:50
[<     inline     >] print_address_description mm/kasan/report.c:147
[<     inline     >] kasan_report_error mm/kasan/report.c:236
[<ffffffc000373dcc>] kasan_report+0x380/0x4b8 mm/kasan/report.c:259
[<     inline     >] check_memory_region mm/kasan/kasan.c:264
[<ffffffc00037352c>] __asan_load8+0x20/0x70 mm/kasan/kasan.c:507
[<ffffffc0005b9624>] memcpy_fromiovec+0x5c/0x114 lib/iovec.c:15
[<     inline     >] memcpy_from_msg include/linux/skbuff.h:2667
[<ffffffc000ddeba0>] ping_common_sendmsg+0x50/0x108 net/ipv4/ping.c:674
[<ffffffc000dded30>] ping_v4_sendmsg+0xd8/0x698 net/ipv4/ping.c:714
[<ffffffc000dc91dc>] inet_sendmsg+0xe0/0x12c net/ipv4/af_inet.c:749
[<     inline     >] __sock_sendmsg_nosec net/socket.c:624
[<     inline     >] __sock_sendmsg net/socket.c:632
[<ffffffc000cab61c>] sock_sendmsg+0x124/0x164 net/socket.c:643
[<     inline     >] SYSC_sendto net/socket.c:1797
[<ffffffc000cad270>] SyS_sendto+0x178/0x1d8 net/socket.c:1761
Memory state around the buggy address:
 ffffffc071077c80: f3 f3 f3 f3 00 00 00 00 00 00 00 00 00 00 f1 f1
 ffffffc071077d00: f1 f1 04 f4 f4 f4 f2 f2 f2 f2 04 f4 f4 f4 f2 f2
>ffffffc071077d80: f2 f2 00 00 f4 f4 f2 f2 f2 f2 00 00 00 00 00 00
                               ^
 ffffffc071077e00: 00 f4 f2 f2 f2 f2 00 00 00 00 00 00 00 00 00 00
 ffffffc071077e80: 00 00 00 00 00 00 f3 f3 f3 f3 00 00 00 00 00 00

Bug: 31349935
Change-Id: Ib7385fc26dfe7e07e9bab42a10ff65a37cbaab54
Signed-off-by: Siqi Lin <siqilin@google.com>
Git-repo: https://android.googlesource.com/kernel/msm


Git-commit: 5459140fb7c8cbb588e06dadb4dc721f0d115c53
Signed-off-by: Dennis Cagle <d-cagle@codeaurora.org>