==================================================================
BUG: KMSAN: uninit-value in INET_ECN_decapsulate include/net/inet_ecn.h:189 [inline]
BUG: KMSAN: uninit-value in IP6_ECN_decapsulate+0x421/0x970 include/net/inet_ecn.h:234
CPU: 0 PID: 30105 Comm: syz-executor1 Not tainted 4.17.0+ #8
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
Call Trace:
 __dump_stack lib/dump_stack.c:77 [inline]
 dump_stack+0x185/0x1d0 lib/dump_stack.c:113
 kmsan_report+0x188/0x2a0 mm/kmsan/kmsan.c:1122
 __msan_warning_32+0x70/0xc0 mm/kmsan/kmsan_instr.c:620
 INET_ECN_decapsulate include/net/inet_ecn.h:189 [inline]
 IP6_ECN_decapsulate+0x421/0x970 include/net/inet_ecn.h:234
 ip6ip6_dscp_ecn_decapsulate+0x1e0/0x250 net/ipv6/ip6_tunnel.c:719
 __ip6_tnl_rcv+0xff9/0x1a10 net/ipv6/ip6_tunnel.c:829
 ip6_tnl_rcv+0xe6/0x110 net/ipv6/ip6_tunnel.c:868
 gre_rcv+0x1661/0x1a90 net/ipv6/ip6_gre.c:534
 ip6_input_finish+0x1353/0x2260 net/ipv6/ip6_input.c:284
 NF_HOOK include/linux/netfilter.h:288 [inline]
 ip6_input net/ipv6/ip6_input.c:327 [inline]
 ip6_mc_input+0xa65/0x10a0 net/ipv6/ip6_input.c:404
 dst_input include/net/dst.h:450 [inline]
 ip6_rcv_finish+0x498/0x6e0 net/ipv6/ip6_input.c:71
 NF_HOOK include/linux/netfilter.h:288 [inline]
 ipv6_rcv+0x1d6b/0x2360 net/ipv6/ip6_input.c:208
 __netif_receive_skb_core+0x47f3/0x4aa0 net/core/dev.c:4592
 __netif_receive_skb net/core/dev.c:4657 [inline]
 netif_receive_skb_internal+0x49d/0x630 net/core/dev.c:4731
 netif_receive_skb+0x240/0x250 net/core/dev.c:4755
 tun_rx_batched drivers/net/tun.c:1563 [inline]
 tun_get_user+0x6b54/0x7f00 drivers/net/tun.c:1970
 tun_chr_write_iter+0x1d4/0x330 drivers/net/tun.c:1998
 call_write_iter include/linux/fs.h:1784 [inline]
 new_sync_write fs/read_write.c:474 [inline]
 __vfs_write+0x808/0x9f0 fs/read_write.c:487
 vfs_write+0x467/0x8c0 fs/read_write.c:549
 ksys_write fs/read_write.c:598 [inline]
 __do_sys_write fs/read_write.c:610 [inline]
 __se_sys_write fs/read_write.c:607 [inline]
 __x64_sys_write+0x1bf/0x3e0 fs/read_write.c:607
 do_syscall_64+0x15b/0x230 arch/x86/entry/common.c:287
 entry_SYSCALL_64_after_hwframe+0x44/0xa9
RIP: 0033:0x455b29
RSP: 002b:00007f4c2c560c68 EFLAGS: 00000246 ORIG_RAX: 0000000000000001
RAX: ffffffffffffffda RBX: 00007f4c2c5616d4 RCX: 0000000000455b29
RDX: 000000000000fdef RSI: 0000000020000100 RDI: 0000000000000014
RBP: 000000000072bea0 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 00000000ffffffff
R13: 00000000004c2659 R14: 00000000004d37c8 R15: 0000000000000000

Uninit was created at:
 kmsan_save_stack_with_flags mm/kmsan/kmsan.c:279 [inline]
 kmsan_internal_poison_shadow+0xb8/0x1b0 mm/kmsan/kmsan.c:189
 kmsan_kmalloc+0x94/0x100 mm/kmsan/kmsan.c:315
 kmsan_slab_alloc+0x10/0x20 mm/kmsan/kmsan.c:322
 slab_post_alloc_hook mm/slab.h:446 [inline]
 slab_alloc_node mm/slub.c:2753 [inline]
 __kmalloc_node_track_caller+0xb35/0x11b0 mm/slub.c:4395
 __kmalloc_reserve net/core/skbuff.c:138 [inline]
 __alloc_skb+0x2cb/0x9e0 net/core/skbuff.c:206
 alloc_skb include/linux/skbuff.h:988 [inline]
 alloc_skb_with_frags+0x1e6/0xb80 net/core/skbuff.c:5254
 sock_alloc_send_pskb+0xb56/0x11a0 net/core/sock.c:2088
 tun_alloc_skb drivers/net/tun.c:1540 [inline]
 tun_get_user+0x21cf/0x7f00 drivers/net/tun.c:1834
 tun_chr_write_iter+0x1d4/0x330 drivers/net/tun.c:1998
 call_write_iter include/linux/fs.h:1784 [inline]
 new_sync_write fs/read_write.c:474 [inline]
 __vfs_write+0x808/0x9f0 fs/read_write.c:487
 vfs_write+0x467/0x8c0 fs/read_write.c:549
 ksys_write fs/read_write.c:598 [inline]
 __do_sys_write fs/read_write.c:610 [inline]
 __se_sys_write fs/read_write.c:607 [inline]
 __x64_sys_write+0x1bf/0x3e0 fs/read_write.c:607
 do_syscall_64+0x15b/0x230 arch/x86/entry/common.c:287
 entry_SYSCALL_64_after_hwframe+0x44/0xa9
==================================================================