KMSAN: uninit-value in ip6_tnl_start_xmit

[syzbot]

Hello,

syzbot found the following crash on:

HEAD commit:    d2d741e5d189 kmsan: add initialization for shmem pages
git tree:       https://github.com/google/kmsan.git/master
console output: https://syzkaller.appspot.com/x/log.txt?x=14094a57800000
kernel config:  https://syzkaller.appspot.com/x/.config?x=48f9de3384bcd0f
dashboard link: https://syzkaller.appspot.com/bug?extid=3fde91d4d394747d6db4
compiler:       clang version 7.0.0 (trunk 329391)
syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=17919a47800000
C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=13598fbb800000

IMPORTANT: if you fix the bug, please add the following tag to the commit:
Reported-by: syzbot+3fde91d4d394747d6db4@xxxxxxxxxxxxxxxxxxxxxxxxx

IPv6: ADDRCONF(NETDEV_UP): veth1: link is not ready
IPv6: ADDRCONF(NETDEV_CHANGE): veth1: link becomes ready
IPv6: ADDRCONF(NETDEV_CHANGE): veth0: link becomes ready
8021q: adding VLAN 0 to HW filter on device team0
==================================================================
BUG: KMSAN: uninit-value in ip6ip6_tnl_xmit net/ipv6/ip6_tunnel.c:1307  
[inline]
BUG: KMSAN: uninit-value in ip6_tnl_start_xmit+0x7d2/0x1ef0  
net/ipv6/ip6_tunnel.c:1390
CPU: 0 PID: 4504 Comm: syz-executor558 Not tainted 4.16.0+ #87
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
 __msan_warning_32+0x6c/0xb0 mm/kmsan/kmsan_instr.c:683
 ip6ip6_tnl_xmit net/ipv6/ip6_tunnel.c:1307 [inline]
 ip6_tnl_start_xmit+0x7d2/0x1ef0 net/ipv6/ip6_tunnel.c:1390
 __netdev_start_xmit include/linux/netdevice.h:4066 [inline]
 netdev_start_xmit include/linux/netdevice.h:4075 [inline]
 xmit_one net/core/dev.c:3026 [inline]
 dev_hard_start_xmit+0x5f1/0xc70 net/core/dev.c:3042
 __dev_queue_xmit+0x27ee/0x3520 net/core/dev.c:3557
 dev_queue_xmit+0x4b/0x60 net/core/dev.c:3590
 packet_snd net/packet/af_packet.c:2944 [inline]
 packet_sendmsg+0x7c70/0x8a30 net/packet/af_packet.c:2969
 sock_sendmsg_nosec net/socket.c:630 [inline]
 sock_sendmsg net/socket.c:640 [inline]
 ___sys_sendmsg+0xec0/0x1310 net/socket.c:2046
 __sys_sendmmsg+0x42d/0x800 net/socket.c:2136
 SYSC_sendmmsg+0xc4/0x110 net/socket.c:2167
 SyS_sendmmsg+0x63/0x90 net/socket.c:2162
 do_syscall_64+0x309/0x430 arch/x86/entry/common.c:287
 entry_SYSCALL_64_after_hwframe+0x3d/0xa2
RIP: 0033:0x441819
RSP: 002b:00007ffe58ee8268 EFLAGS: 00000213 ORIG_RAX: 0000000000000133
RAX: ffffffffffffffda RBX: 0000000000000003 RCX: 0000000000441819
RDX: 0000000000000002 RSI: 0000000020000100 RDI: 0000000000000003
RBP: 00000000006cd018 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000213 R12: 0000000000402510
R13: 00000000004025a0 R14: 0000000000000000 R15: 0000000000000000

Uninit was created at:
 kmsan_save_stack_with_flags mm/kmsan/kmsan.c:278 [inline]
 kmsan_internal_poison_shadow+0xb8/0x1b0 mm/kmsan/kmsan.c:188
 kmsan_kmalloc+0x94/0x100 mm/kmsan/kmsan.c:314
 kmsan_slab_alloc+0x11/0x20 mm/kmsan/kmsan.c:321
 slab_post_alloc_hook mm/slab.h:445 [inline]
 slab_alloc_node mm/slub.c:2737 [inline]
 __kmalloc_node_track_caller+0xaed/0x11c0 mm/slub.c:4369
 __kmalloc_reserve net/core/skbuff.c:138 [inline]
 __alloc_skb+0x2cf/0x9f0 net/core/skbuff.c:206
 alloc_skb include/linux/skbuff.h:984 [inline]
 alloc_skb_with_frags+0x1d4/0xb20 net/core/skbuff.c:5234
 sock_alloc_send_pskb+0xb56/0x1190 net/core/sock.c:2085
 packet_alloc_skb net/packet/af_packet.c:2803 [inline]
 packet_snd net/packet/af_packet.c:2894 [inline]
 packet_sendmsg+0x6454/0x8a30 net/packet/af_packet.c:2969
 sock_sendmsg_nosec net/socket.c:630 [inline]
 sock_sendmsg net/socket.c:640 [inline]
 ___sys_sendmsg+0xec0/0x1310 net/socket.c:2046
 __sys_sendmmsg+0x42d/0x800 net/socket.c:2136
 SYSC_sendmmsg+0xc4/0x110 net/socket.c:2167
 SyS_sendmmsg+0x63/0x90 net/socket.c:2162
 do_syscall_64+0x309/0x430 arch/x86/entry/common.c:287
 entry_SYSCALL_64_after_hwframe+0x3d/0xa2
==================================================================


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