Re: KASAN: use-after-free Read in sit_tunnel_xmit

[Cong Wang]

On Tue, Feb 13, 2018 at 10:48 AM, Dmitry Vyukov <dvyukov@xxxxxxxxxx> wrote:
> On Mon, Oct 30, 2017 at 7:41 PM, Cong Wang <xiyou.wangcong@xxxxxxxxx> wrote:
>> On Mon, Oct 30, 2017 at 8:34 AM, syzbot
>> <bot+1aa412fe58f4059538c0204a0f096524e6dce60b@xxxxxxxxxxxxxxxxxxxxxxxxx>
>> wrote:
>>> Hello,
>>>
>>> syzkaller hit the following crash on
>>> 4dc12ffeaeac939097a3f55c881d3dc3523dff0c
>>> git://git.kernel.org/pub/scm/linux/kernel/git/davem/net-next.git/master
>>> compiler: gcc (GCC) 7.1.1 20170620
>>> .config is attached
>>> Raw console output is attached.
>>>
>>> skbuff: bad partial csum: csum=53081/14726 len=2273
>>> ==================================================================
>>> BUG: KASAN: use-after-free in ipv6_get_dsfield include/net/dsfield.h:23
>>> [inline]
>>> BUG: KASAN: use-after-free in ipip6_tunnel_xmit net/ipv6/sit.c:968 [inline]
>>> BUG: KASAN: use-after-free in sit_tunnel_xmit+0x2a41/0x3130
>>> net/ipv6/sit.c:1016
>>> Read of size 2 at addr ffff8801c64afd00 by task syz-executor3/16942
>>>
>>> CPU: 0 PID: 16942 Comm: syz-executor3 Not tainted 4.14.0-rc5+ #97
>>> Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS
>>> Google 01/01/2011
>>> Call Trace:
>>>  __dump_stack lib/dump_stack.c:16 [inline]
>>>  dump_stack+0x194/0x257 lib/dump_stack.c:52
>>>  print_address_description+0x73/0x250 mm/kasan/report.c:252
>>>  kasan_report_error mm/kasan/report.c:351 [inline]
>>>  kasan_report+0x25b/0x340 mm/kasan/report.c:409
>>>  __asan_report_load2_noabort+0x14/0x20 mm/kasan/report.c:428
>>>  ipv6_get_dsfield include/net/dsfield.h:23 [inline]
>>>  ipip6_tunnel_xmit net/ipv6/sit.c:968 [inline]
>>>  sit_tunnel_xmit+0x2a41/0x3130 net/ipv6/sit.c:1016
>>>  __netdev_start_xmit include/linux/netdevice.h:4022 [inline]
>>>  netdev_start_xmit include/linux/netdevice.h:4031 [inline]
>>>  xmit_one net/core/dev.c:3008 [inline]
>>>  dev_hard_start_xmit+0x248/0xac0 net/core/dev.c:3024
>>>  __dev_queue_xmit+0x17d2/0x2070 net/core/dev.c:3505
>>>  dev_queue_xmit+0x17/0x20 net/core/dev.c:3538
>>>  neigh_direct_output+0x15/0x20 net/core/neighbour.c:1390
>>>  neigh_output include/net/neighbour.h:481 [inline]
>>>  ip6_finish_output2+0xad1/0x22a0 net/ipv6/ip6_output.c:120
>>>  ip6_fragment+0x25ae/0x3420 net/ipv6/ip6_output.c:723
>>>  ip6_finish_output+0x319/0x920 net/ipv6/ip6_output.c:144
>>>  NF_HOOK_COND include/linux/netfilter.h:238 [inline]
>>>  ip6_output+0x1f4/0x850 net/ipv6/ip6_output.c:163
>>>  dst_output include/net/dst.h:459 [inline]
>>>  ip6_local_out+0x95/0x160 net/ipv6/output_core.c:176
>>>  ip6_send_skb+0xa1/0x330 net/ipv6/ip6_output.c:1658
>>>  ip6_push_pending_frames+0xb3/0xe0 net/ipv6/ip6_output.c:1678
>>>  rawv6_push_pending_frames net/ipv6/raw.c:616 [inline]
>>>  rawv6_sendmsg+0x2eb9/0x3e40 net/ipv6/raw.c:935
>>>  inet_sendmsg+0x11f/0x5e0 net/ipv4/af_inet.c:763
>>>  sock_sendmsg_nosec net/socket.c:633 [inline]
>>>  sock_sendmsg+0xca/0x110 net/socket.c:643
>>>  SYSC_sendto+0x352/0x5a0 net/socket.c:1750
>>>  SyS_sendto+0x40/0x50 net/socket.c:1718
>>>  entry_SYSCALL_64_fastpath+0x1f/0xbe
>>> RIP: 0033:0x452869
>>> RSP: 002b:00007fe3c12e5be8 EFLAGS: 00000212 ORIG_RAX: 000000000000002c
>>> RAX: ffffffffffffffda RBX: 00000000007580d8 RCX: 0000000000452869
>>> RDX: 00000000000007f1 RSI: 000000002013b7ff RDI: 0000000000000014
>>> RBP: 0000000000000161 R08: 00000000204e8fe4 R09: 000000000000001c
>>> R10: 0000000001000000 R11: 0000000000000212 R12: 00000000006f01b8
>>> R13: 00000000ffffffff R14: 00007fe3c12e66d4 R15: 0000000000000017
>>>
>>> Allocated by task 16924:
>>>  save_stack_trace+0x16/0x20 arch/x86/kernel/stacktrace.c:59
>>>  save_stack+0x43/0xd0 mm/kasan/kasan.c:447
>>>  set_track mm/kasan/kasan.c:459 [inline]
>>>  kasan_kmalloc+0xad/0xe0 mm/kasan/kasan.c:551
>>>  __do_kmalloc_node mm/slab.c:3689 [inline]
>>>  __kmalloc_node_track_caller+0x47/0x70 mm/slab.c:3703
>>>  __kmalloc_reserve.isra.40+0x41/0xd0 net/core/skbuff.c:138
>>>  __alloc_skb+0x13b/0x780 net/core/skbuff.c:206
>>>  alloc_skb include/linux/skbuff.h:985 [inline]
>>>  sock_wmalloc+0x140/0x1d0 net/core/sock.c:1932
>>>  __ip6_append_data.isra.43+0x2681/0x3340 net/ipv6/ip6_output.c:1397
>>>  ip6_append_data+0x189/0x290 net/ipv6/ip6_output.c:1552
>>>  rawv6_sendmsg+0x1dd9/0x3e40 net/ipv6/raw.c:928
>>>  inet_sendmsg+0x11f/0x5e0 net/ipv4/af_inet.c:763
>>>  sock_sendmsg_nosec net/socket.c:633 [inline]
>>>  sock_sendmsg+0xca/0x110 net/socket.c:643
>>>  SYSC_sendto+0x352/0x5a0 net/socket.c:1750
>>>  SyS_sendto+0x40/0x50 net/socket.c:1718
>>>  entry_SYSCALL_64_fastpath+0x1f/0xbe
>>>
>>> Freed by task 16942:
>>>  save_stack_trace+0x16/0x20 arch/x86/kernel/stacktrace.c:59
>>>  save_stack+0x43/0xd0 mm/kasan/kasan.c:447
>>>  set_track mm/kasan/kasan.c:459 [inline]
>>>  kasan_slab_free+0x71/0xc0 mm/kasan/kasan.c:524
>>>  __cache_free mm/slab.c:3503 [inline]
>>>  kfree+0xca/0x250 mm/slab.c:3820
>>>  skb_free_head+0x74/0xb0 net/core/skbuff.c:554
>>>  pskb_expand_head+0x36b/0x1210 net/core/skbuff.c:1494
>>>  __pskb_pull_tail+0x14a/0x17c0 net/core/skbuff.c:1877
>>>  pskb_may_pull include/linux/skbuff.h:2102 [inline]
>>>  _decode_session6+0x8a4/0x1100 net/ipv6/xfrm6_policy.c:148
>>
>> Looks like we should indicate error by returning some int
>> for afinfo->decode_session().
>
>
> Cong, do you want to do something with this bug? Otherwise I want to
> close this as part of old bug bankruptcy.

I will work on a patch to address this.

Thanks.