Subject: Re: KMSAN: uninit-value in _decode_session6

From: syzbot <[email-masked]>
Date: Tue, 01 May 2018 02:12:02 -0700

syzbot has found a reproducer for 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?id=6550343064223744
kernel config:   
https://syzkaller.appspot.com/x/.config?id=328654897048964367
dashboard link: https://syzkaller.appspot.com/bug?extid=2974b85346f85b586f4d
compiler:       clang version 7.0.0 (trunk 329391)
syzkaller  
repro:https://syzkaller.appspot.com/x/repro.syz?id=5023772637659136
C reproducer:   https://syzkaller.appspot.com/x/repro.c?id=5102535626981376

IMPORTANT: if you fix the bug, please add the following tag to the commit:
Reported-by: [email-masked]

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 _decode_session6+0x6d2/0x16e0  
net/ipv6/xfrm6_policy.c:151
CPU: 0 PID: 4529 Comm: syz-executor165 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
  _decode_session6+0x6d2/0x16e0 net/ipv6/xfrm6_policy.c:151
  __xfrm_decode_session+0x151/0x200 net/xfrm/xfrm_policy.c:2368
  xfrm_decode_session_reverse include/net/xfrm.h:1213 [inline]
  icmpv6_route_lookup net/ipv6/icmp.c:372 [inline]
  icmp6_send+0x2bf7/0x3730 net/ipv6/icmp.c:551
  icmpv6_send+0xe0/0x110 net/ipv6/ip6_icmp.c:43
  ip6_link_failure+0x8f/0x580 net/ipv6/route.c:2034
  dst_link_failure include/net/dst.h:426 [inline]
  ip6_tnl_xmit+0x1423/0x3af0 net/ipv6/ip6_tunnel.c:1215
  ip6ip6_tnl_xmit net/ipv6/ip6_tunnel.c:1367 [inline]
  ip6_tnl_start_xmit+0x1cc0/0x1ef0 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
  neigh_direct_output+0x42/0x50 net/core/neighbour.c:1390
  neigh_output include/net/neighbour.h:482 [inline]
  ip6_finish_output2+0x1d01/0x2130 net/ipv6/ip6_output.c:120
  ip6_finish_output+0xae9/0xba0 net/ipv6/ip6_output.c:154
  NF_HOOK_COND include/linux/netfilter.h:277 [inline]
  ip6_output+0x597/0x6c0 net/ipv6/ip6_output.c:171
  dst_output include/net/dst.h:443 [inline]
  ip6_local_out+0x15e/0x1d0 net/ipv6/output_core.c:176
  ip6_send_skb net/ipv6/ip6_output.c:1682 [inline]
  ip6_push_pending_frames+0x218/0x4d0 net/ipv6/ip6_output.c:1702
  rawv6_push_pending_frames net/ipv6/raw.c:616 [inline]
  rawv6_sendmsg+0x4235/0x4fb0 net/ipv6/raw.c:935
  inet_sendmsg+0x48d/0x740 net/ipv4/af_inet.c:764
  sock_sendmsg_nosec net/socket.c:630 [inline]
  sock_sendmsg net/socket.c:640 [inline]
  sock_write_iter+0x3b9/0x470 net/socket.c:909
  call_write_iter include/linux/fs.h:1782 [inline]
  new_sync_write fs/read_write.c:469 [inline]
  __vfs_write+0x7fb/0x9f0 fs/read_write.c:482
  vfs_write+0x463/0x8d0 fs/read_write.c:544
  SYSC_write+0x172/0x360 fs/read_write.c:589
  SyS_write+0x55/0x80 fs/read_write.c:581
  do_syscall_64+0x309/0x430 arch/x86/entry/common.c:287
  entry_SYSCALL_64_after_hwframe+0x3d/0xa2
RIP: 0033:0x4418b9
RSP: 002b:00007ffece331e68 EFLAGS: 00000217 ORIG_RAX: 0000000000000001
RAX: ffffffffffffffda RBX: 0000000000000003 RCX: 00000000004418b9
RDX: 000000000000036b RSI: 0000000020000240 RDI: 0000000000000004
RBP: 00000000006cd018 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000217 R12: 00000000004025b0
R13: 0000000000402640 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]
  pskb_expand_head+0x21d/0x1a70 net/core/skbuff.c:1458
  __pskb_pull_tail+0x1d7/0x2300 net/core/skbuff.c:1878
  pskb_may_pull include/linux/skbuff.h:2112 [inline]
  ip6_tnl_parse_tlv_enc_lim+0x7f5/0xa90 net/ipv6/ip6_tunnel.c:411
  ip6ip6_tnl_xmit net/ipv6/ip6_tunnel.c:1326 [inline]
  ip6_tnl_start_xmit+0x911/0x1ef0 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
  neigh_direct_output+0x42/0x50 net/core/neighbour.c:1390
  neigh_output include/net/neighbour.h:482 [inline]
  ip6_finish_output2+0x1d01/0x2130 net/ipv6/ip6_output.c:120
  ip6_finish_output+0xae9/0xba0 net/ipv6/ip6_output.c:154
  NF_HOOK_COND include/linux/netfilter.h:277 [inline]
  ip6_output+0x597/0x6c0 net/ipv6/ip6_output.c:171
  dst_output include/net/dst.h:443 [inline]
  ip6_local_out+0x15e/0x1d0 net/ipv6/output_core.c:176
  ip6_send_skb net/ipv6/ip6_output.c:1682 [inline]
  ip6_push_pending_frames+0x218/0x4d0 net/ipv6/ip6_output.c:1702
  rawv6_push_pending_frames net/ipv6/raw.c:616 [inline]
  rawv6_sendmsg+0x4235/0x4fb0 net/ipv6/raw.c:935
  inet_sendmsg+0x48d/0x740 net/ipv4/af_inet.c:764
  sock_sendmsg_nosec net/socket.c:630 [inline]
  sock_sendmsg net/socket.c:640 [inline]
  sock_write_iter+0x3b9/0x470 net/socket.c:909
  call_write_iter include/linux/fs.h:1782 [inline]
  new_sync_write fs/read_write.c:469 [inline]
  __vfs_write+0x7fb/0x9f0 fs/read_write.c:482
  vfs_write+0x463/0x8d0 fs/read_write.c:544
  SYSC_write+0x172/0x360 fs/read_write.c:589
  SyS_write+0x55/0x80 fs/read_write.c:581
  do_syscall_64+0x309/0x430 arch/x86/entry/common.c:287
  entry_SYSCALL_64_after_hwframe+0x3d/0xa2
==================================================================