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SubjectKMSAN: uninit-value in _copy_to_iter (2)

syzbot hit the following crash on commit
d2d741e5d1898dfde1a75ea3d29a9a3e2edf0617 (Sun Apr 22 15:05:22 2018 +0000)
kmsan: add initialization for shmem pages
syzbot dashboard link:

Unfortunately, I don't have any reproducer for this crash yet.
Raw console output:
Kernel config:
compiler: clang version 7.0.0 (trunk 329391)

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BUG: KMSAN: uninit-value in copyout lib/iov_iter.c:140 [inline]
BUG: KMSAN: uninit-value in _copy_to_iter+0x1bb3/0x28f0 lib/iov_iter.c:571
CPU: 0 PID: 7670 Comm: syz-executor7 Not tainted 4.16.0+ #86
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS
Google 01/01/2011
Call Trace:
__dump_stack lib/dump_stack.c:17 [inline]
dump_stack+0x185/0x1d0 lib/dump_stack.c:53
kmsan_report+0x142/0x240 mm/kmsan/kmsan.c:1067
kmsan_internal_check_memory+0x135/0x1e0 mm/kmsan/kmsan.c:1157
kmsan_copy_to_user+0x69/0x160 mm/kmsan/kmsan.c:1199
copyout lib/iov_iter.c:140 [inline]
_copy_to_iter+0x1bb3/0x28f0 lib/iov_iter.c:571
copy_to_iter include/linux/uio.h:106 [inline]
skb_copy_datagram_iter+0x443/0xf70 net/core/datagram.c:431
skb_copy_datagram_msg include/linux/skbuff.h:3264 [inline]
netlink_recvmsg+0x6f1/0x1900 net/netlink/af_netlink.c:1958
sock_recvmsg_nosec net/socket.c:803 [inline]
sock_recvmsg+0x1d0/0x230 net/socket.c:810
___sys_recvmsg+0x3fb/0x810 net/socket.c:2205
__sys_recvmmsg+0x54e/0xdb0 net/socket.c:2313
SYSC_recvmmsg+0x29b/0x3e0 net/socket.c:2394
SyS_recvmmsg+0x76/0xa0 net/socket.c:2378
do_syscall_64+0x309/0x430 arch/x86/entry/common.c:287
RIP: 0033:0x455389
RSP: 002b:00007f0281d3dc68 EFLAGS: 00000246 ORIG_RAX: 000000000000012b
RAX: ffffffffffffffda RBX: 00007f0281d3e6d4 RCX: 0000000000455389
RDX: 0000000000000003 RSI: 0000000020001f80 RDI: 0000000000000014
RBP: 000000000072bea0 R08: 0000000020002040 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 00000000ffffffff
R13: 000000000000049e R14: 00000000006f9f70 R15: 0000000000000000

Uninit was stored to memory at:
kmsan_save_stack_with_flags mm/kmsan/kmsan.c:278 [inline]
kmsan_save_stack mm/kmsan/kmsan.c:293 [inline]
kmsan_internal_chain_origin+0x12b/0x210 mm/kmsan/kmsan.c:684
kmsan_memcpy_origins+0x11d/0x170 mm/kmsan/kmsan.c:526
__msan_memcpy+0x109/0x160 mm/kmsan/kmsan_instr.c:477
__nla_put lib/nlattr.c:569 [inline]
nla_put+0x276/0x340 lib/nlattr.c:627
copy_to_user_policy_type net/xfrm/xfrm_user.c:1678 [inline]
build_acquire net/xfrm/xfrm_user.c:2850 [inline]
xfrm_send_acquire+0x1068/0x1690 net/xfrm/xfrm_user.c:2873
km_query net/xfrm/xfrm_state.c:1953 [inline]
xfrm_state_find+0x3ad8/0x4f40 net/xfrm/xfrm_state.c:1021
xfrm_tmpl_resolve_one net/xfrm/xfrm_policy.c:1393 [inline]
xfrm_tmpl_resolve net/xfrm/xfrm_policy.c:1437 [inline]
xfrm_resolve_and_create_bundle+0xc31/0x5270 net/xfrm/xfrm_policy.c:1833
xfrm_lookup+0x606/0x39d0 net/xfrm/xfrm_policy.c:2163
xfrm_lookup_route+0xfa/0x360 net/xfrm/xfrm_policy.c:2283
ip6_dst_lookup_flow+0x221/0x270 net/ipv6/ip6_output.c:1099
ip6_datagram_dst_update+0x93a/0x1470 net/ipv6/datagram.c:91
__ip6_datagram_connect+0x14f6/0x1a20 net/ipv6/datagram.c:257
ip6_datagram_connect net/ipv6/datagram.c:280 [inline]
ip6_datagram_connect_v6_only+0x104/0x180 net/ipv6/datagram.c:292
inet_dgram_connect+0x2e8/0x4d0 net/ipv4/af_inet.c:542
SYSC_connect+0x41a/0x510 net/socket.c:1639
SyS_connect+0x54/0x80 net/socket.c:1620
do_syscall_64+0x309/0x430 arch/x86/entry/common.c:287
Local variable description: ----upt.i.i@xfrm_send_acquire
Variable was created at:
xfrm_send_acquire+0x73/0x1690 net/xfrm/xfrm_user.c:2864
km_query net/xfrm/xfrm_state.c:1953 [inline]
xfrm_state_find+0x3ad8/0x4f40 net/xfrm/xfrm_state.c:1021

Byte 200 of 207 is uninitialized
FAULT_INJECTION: forcing a failure.
name failslab, interval 1, probability 0, space 0, times 0
CPU: 1 PID: 7675 Comm: syz-executor3 Not tainted 4.16.0+ #86

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