Re: KMSAN: uninit-value in __netif_receive_skb_core

[Toshiaki Makita]

On 2018/04/12 17:03, Dmitry Vyukov wrote:
> On Thu, Apr 12, 2018 at 10:01 AM, syzbot
> <syzbot+b202b7208664142954fa@xxxxxxxxxxxxxxxxxxxxxxxxx> wrote:
>> Hello,
>>
>> syzbot hit the following crash on https://github.com/google/kmsan.git/master
>> commit
>> e2ab7e8abba47a2f2698216258e5d8727ae58717 (Fri Apr 6 16:24:31 2018 +0000)
>> kmsan: temporarily disable visitAsmInstruction() to help syzbot
>> syzbot dashboard link:
>> https://syzkaller.appspot.com/bug?extid=b202b7208664142954fa
>>
>> Unfortunately, I don't have any reproducer for this crash yet.
>> Raw console output:
>> https://syzkaller.appspot.com/x/log.txt?id=5356516437655552
>> Kernel config:
>> https://syzkaller.appspot.com/x/.config?id=6627248707860932248
>> compiler: clang version 7.0.0 (trunk 329391)
> 
> +Toshiaki as this seems to be related to the recent vlan tagging changes.

seems not...
"Uninit was stored to memory at:" shows uninitialized memory was stored
before where I modified the code (skb_reorder_vlan_header).

I'm not sure what this uninit memory means.
To me it looks like the memory is initialized by user provided data.

(iov in packet sock -> skb->data -> skb->protocol)

The reproducer provides 4 bytes after ethernet header, so it should be
sufficient for a vlan tag. This will set skb->len to 4 and fill the
4-byte contents in packet_snd(). skb_vlan_untag() is reading the user
provided 4-byte skb->data. It is ensured that skb_vlan_untag() does not
read beyond skb->len since it calls pskb_may_pull(). At this point I am
failing to find what I am missing.

> This also seems to be related to
> https://groups.google.com/d/msg/syzkaller-bugs/VRH9NnUi2k0/90GYsAeRBgAJ
> 
>> IMPORTANT: if you fix the bug, please add the following tag to the commit:
>> Reported-by: syzbot+b202b7208664142954fa@xxxxxxxxxxxxxxxxxxxxxxxxx
>> It will help syzbot understand when the bug is fixed. See footer for
>> details.
>> If you forward the report, please keep this part and the footer.
>>
>> ==================================================================
>> BUG: KMSAN: uninit-value in __read_once_size include/linux/compiler.h:197
>> [inline]
>> BUG: KMSAN: uninit-value in deliver_ptype_list_skb net/core/dev.c:1908
>> [inline]
>> BUG: KMSAN: uninit-value in __netif_receive_skb_core+0x4630/0x4a80
>> net/core/dev.c:4545
>> CPU: 0 PID: 5999 Comm: syz-executor3 Not tainted 4.16.0+ #82
>> Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS
>> Google 01/01/2011
>> Call Trace:
>>  <IRQ>
>>  __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:676
>>  __read_once_size include/linux/compiler.h:197 [inline]
>>  deliver_ptype_list_skb net/core/dev.c:1908 [inline]
>>  __netif_receive_skb_core+0x4630/0x4a80 net/core/dev.c:4545
>>  __netif_receive_skb net/core/dev.c:4627 [inline]
>>  process_backlog+0x62d/0xe20 net/core/dev.c:5307
>>  napi_poll net/core/dev.c:5705 [inline]
>>  net_rx_action+0x7c1/0x1a70 net/core/dev.c:5771
>>  __do_softirq+0x56d/0x93d kernel/softirq.c:285
>>  do_softirq_own_stack+0x2a/0x40 arch/x86/entry/entry_64.S:1040
>>  </IRQ>
>>  do_softirq kernel/softirq.c:329 [inline]
>>  __local_bh_enable_ip+0x114/0x140 kernel/softirq.c:182
>>  local_bh_enable+0x36/0x40 include/linux/bottom_half.h:32
>>  rcu_read_unlock_bh include/linux/rcupdate.h:726 [inline]
>>  __dev_queue_xmit+0x2a31/0x2b60 net/core/dev.c:3584
>>  dev_queue_xmit+0x4b/0x60 net/core/dev.c:3590
>>  packet_snd net/packet/af_packet.c:2944 [inline]
>>  packet_sendmsg+0x7c57/0x8a10 net/packet/af_packet.c:2969
>>  sock_sendmsg_nosec net/socket.c:630 [inline]
>>  sock_sendmsg net/socket.c:640 [inline]
>>  sock_write_iter+0x3b9/0x470 net/socket.c:909
>>  do_iter_readv_writev+0x7bb/0x970 include/linux/fs.h:1776
>>  do_iter_write+0x30d/0xd40 fs/read_write.c:932
>>  vfs_writev fs/read_write.c:977 [inline]
>>  do_writev+0x3c9/0x830 fs/read_write.c:1012
>>  SYSC_writev+0x9b/0xb0 fs/read_write.c:1085
>>  SyS_writev+0x56/0x80 fs/read_write.c:1082
>>  do_syscall_64+0x309/0x430 arch/x86/entry/common.c:287
>>  entry_SYSCALL_64_after_hwframe+0x3d/0xa2
>> RIP: 0033:0x455259
>> RSP: 002b:00007fb53ede8c68 EFLAGS: 00000246 ORIG_RAX: 0000000000000014
>> RAX: ffffffffffffffda RBX: 00007fb53ede96d4 RCX: 0000000000455259
>> RDX: 0000000000000001 RSI: 00000000200010c0 RDI: 0000000000000013
>> RBP: 000000000072bea0 R08: 0000000000000000 R09: 0000000000000000
>> R10: 0000000000000000 R11: 0000000000000246 R12: 00000000ffffffff
>> R13: 00000000000006cd R14: 00000000006fd3d8 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
>>  __msan_chain_origin+0x69/0xc0 mm/kmsan/kmsan_instr.c:521
>>  skb_vlan_untag+0x950/0xee0 include/linux/if_vlan.h:597
>>  __netif_receive_skb_core+0x70a/0x4a80 net/core/dev.c:4460
>>  __netif_receive_skb net/core/dev.c:4627 [inline]
>>  process_backlog+0x62d/0xe20 net/core/dev.c:5307
>>  napi_poll net/core/dev.c:5705 [inline]
>>  net_rx_action+0x7c1/0x1a70 net/core/dev.c:5771
>>  __do_softirq+0x56d/0x93d kernel/softirq.c:285
>> 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+0x6444/0x8a10 net/packet/af_packet.c:2969
>>  sock_sendmsg_nosec net/socket.c:630 [inline]
>>  sock_sendmsg net/socket.c:640 [inline]
>>  sock_write_iter+0x3b9/0x470 net/socket.c:909
>>  do_iter_readv_writev+0x7bb/0x970 include/linux/fs.h:1776
>>  do_iter_write+0x30d/0xd40 fs/read_write.c:932
>>  vfs_writev fs/read_write.c:977 [inline]
>>  do_writev+0x3c9/0x830 fs/read_write.c:1012
>>  SYSC_writev+0x9b/0xb0 fs/read_write.c:1085
>>  SyS_writev+0x56/0x80 fs/read_write.c:1082
>>  do_syscall_64+0x309/0x430 arch/x86/entry/common.c:287
>>  entry_SYSCALL_64_after_hwframe+0x3d/0xa2
>> ==================================================================
>>
>>
>> ---
>> This bug is generated by a dumb bot. It may contain errors.
>> See https://goo.gl/tpsmEJ for details.
>> Direct all questions to syzkaller@xxxxxxxxxxxxxxxxx
>>
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>> If you forgot to add the Reported-by tag, once the fix for this bug is
>> merged
>> into any tree, please reply to this email with:
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> 
> 

-- 
Toshiaki Makita