KMSAN: uninit-value in sit_tunnel_xmit

[syzbot]

Hello,

syzbot found the following crash on:

HEAD commit:    d1c2a46a46f6 kmsan: update LLVM/Clang patches to r337583.
git tree:       https://github.com/google/kmsan.git/master
console output: https://syzkaller.appspot.com/x/log.txt?x=17d4570c400000
kernel config:  https://syzkaller.appspot.com/x/.config?x=31cf75cbffdedb44
dashboard link: https://syzkaller.appspot.com/bug?extid=782ee96f9147673d8822
compiler:       clang version 7.0.0 (trunk 334104)

Unfortunately, I don't have any reproducer for this crash yet.

IMPORTANT: if you fix the bug, please add the following tag to the commit:
Reported-by: syzbot+782ee96f9147673d8822@xxxxxxxxxxxxxxxxxxxxxxxxx

IPVS: Scheduler module ip_vs_mh not found
==================================================================
BUG: KMSAN: uninit-value in __ipv6_prefix_equal64_half  
include/net/ipv6.h:522 [inline]
BUG: KMSAN: uninit-value in ipv6_prefix_equal include/net/ipv6.h:539  
[inline]
BUG: KMSAN: uninit-value in check_6rd net/ipv6/sit.c:771 [inline]
BUG: KMSAN: uninit-value in try_6rd net/ipv6/sit.c:805 [inline]
BUG: KMSAN: uninit-value in ipip6_tunnel_xmit net/ipv6/sit.c:865 [inline]
BUG: KMSAN: uninit-value in sit_tunnel_xmit+0x1ad3/0x3b00  
net/ipv6/sit.c:1029
CPU: 0 PID: 7135 Comm: syz-executor4 Not tainted 4.18.0-rc5+ #29
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+0x185/0x1e0 lib/dump_stack.c:113
 kmsan_report+0x195/0x2c0 mm/kmsan/kmsan.c:982
 __msan_warning+0x7d/0xe0 mm/kmsan/kmsan_instr.c:645
IPVS: Scheduler module ip_vs_mh not found
 __ipv6_prefix_equal64_half include/net/ipv6.h:522 [inline]
 ipv6_prefix_equal include/net/ipv6.h:539 [inline]
 check_6rd net/ipv6/sit.c:771 [inline]
 try_6rd net/ipv6/sit.c:805 [inline]
 ipip6_tunnel_xmit net/ipv6/sit.c:865 [inline]
 sit_tunnel_xmit+0x1ad3/0x3b00 net/ipv6/sit.c:1029
 __netdev_start_xmit include/linux/netdevice.h:4148 [inline]
 netdev_start_xmit include/linux/netdevice.h:4157 [inline]
 xmit_one net/core/dev.c:3034 [inline]
 dev_hard_start_xmit+0x60f/0xcc0 net/core/dev.c:3050
 __dev_queue_xmit+0x3060/0x3c70 net/core/dev.c:3569
 dev_queue_xmit+0x4b/0x60 net/core/dev.c:3602
 packet_snd net/packet/af_packet.c:2919 [inline]
 packet_sendmsg+0x8469/0x9010 net/packet/af_packet.c:2944
 sock_sendmsg_nosec net/socket.c:641 [inline]
 sock_sendmsg net/socket.c:651 [inline]
 ___sys_sendmsg+0xed9/0x1350 net/socket.c:2125
 __sys_sendmsg net/socket.c:2163 [inline]
 __do_sys_sendmsg net/socket.c:2172 [inline]
 __se_sys_sendmsg net/socket.c:2170 [inline]
 __x64_sys_sendmsg+0x3b0/0x520 net/socket.c:2170
 do_syscall_64+0x15b/0x230 arch/x86/entry/common.c:290
 entry_SYSCALL_64_after_hwframe+0x63/0xe7
RIP: 0033:0x455ab9
Code: 1d ba fb ff c3 66 2e 0f 1f 84 00 00 00 00 00 66 90 48 89 f8 48 89 f7  
48 89 d6 48 89 ca 4d 89 c2 4d 89 c8 4c 8b 4c 24 08 0f 05 <48> 3d 01 f0 ff  
ff 0f 83 eb b9 fb ff c3 66 2e 0f 1f 84 00 00 00 00
RSP: 002b:00007f68d21b1c68 EFLAGS: 00000246 ORIG_RAX: 000000000000002e
RAX: ffffffffffffffda RBX: 00007f68d21b26d4 RCX: 0000000000455ab9
RDX: 0000000000000000 RSI: 0000000020000000 RDI: 0000000000000013
RBP: 000000000072bea0 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 00000000ffffffff
R13: 00000000004c1066 R14: 00000000004d16c8 R15: 0000000000000000

Uninit was created at:
 kmsan_save_stack_with_flags mm/kmsan/kmsan.c:256 [inline]
 kmsan_internal_poison_shadow+0xc8/0x1d0 mm/kmsan/kmsan.c:181
 kmsan_kmalloc+0xa1/0x120 mm/kmsan/kmsan_hooks.c:91
 kmsan_slab_alloc+0x10/0x20 mm/kmsan/kmsan_hooks.c:100
 slab_post_alloc_hook mm/slab.h:446 [inline]
 slab_alloc_node mm/slub.c:2720 [inline]
 __kmalloc_node_track_caller+0xb48/0x11d0 mm/slub.c:4353
 __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:5271
 sock_alloc_send_pskb+0xb59/0x11e0 net/core/sock.c:2095
 packet_alloc_skb net/packet/af_packet.c:2776 [inline]
 packet_snd net/packet/af_packet.c:2867 [inline]
 packet_sendmsg+0x68cb/0x9010 net/packet/af_packet.c:2944
 sock_sendmsg_nosec net/socket.c:641 [inline]
 sock_sendmsg net/socket.c:651 [inline]
 ___sys_sendmsg+0xed9/0x1350 net/socket.c:2125
 __sys_sendmsg net/socket.c:2163 [inline]
 __do_sys_sendmsg net/socket.c:2172 [inline]
 __se_sys_sendmsg net/socket.c:2170 [inline]
 __x64_sys_sendmsg+0x3b0/0x520 net/socket.c:2170
 do_syscall_64+0x15b/0x230 arch/x86/entry/common.c:290
 entry_SYSCALL_64_after_hwframe+0x63/0xe7
==================================================================


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