Date:   Mon, 10 Apr 2017 19:46:22 +0200
From:   Andrey Konovalov <andreyknvl@...gle.com>
To:     Cong Wang <xiyou.wangcong@...il.com>
Cc:     "David S. Miller" <davem@...emloft.net>,
        Alexey Kuznetsov <kuznet@....inr.ac.ru>,
        James Morris <jmorris@...ei.org>,
        Hideaki YOSHIFUJI <yoshfuji@...ux-ipv6.org>,
        Patrick McHardy <kaber@...sh.net>,
        netdev <netdev@...r.kernel.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Eric Dumazet <edumazet@...gle.com>,
        Dmitry Vyukov <dvyukov@...gle.com>,
        Kostya Serebryany <kcc@...gle.com>,
        syzkaller <syzkaller@...glegroups.com>
Subject: Re: net/ipv4: use-after-free in ip_queue_xmit

On Mon, Apr 10, 2017 at 7:42 PM, Cong Wang <xiyou.wangcong@...il.com> wrote:
> On Mon, Apr 10, 2017 at 7:40 AM, Andrey Konovalov <andreyknvl@...gle.com> wrote:
>> Hi,
>>
>> I've got the following error report while fuzzing the kernel with syzkaller.
>>
>> On commit 39da7c509acff13fc8cb12ec1bb20337c988ed36 (4.11-rc6).
>>
>> Unfortunately it's not reproducible.
>>
>> BUG: KASAN: use-after-free in ip_select_ttl include/net/dst.h:176
>> [inline] at addr ffff88006ab3602c
>> BUG: KASAN: use-after-free in ip_queue_xmit+0x1817/0x1a30
>> net/ipv4/ip_output.c:485 at addr ffff88006ab3602c
>> Read of size 4 by task syz-executor1/12627
>> CPU: 3 PID: 12627 Comm: syz-executor1 Not tainted 4.11.0-rc6+ #206
>> Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS Bochs 01/01/2011
>> Call Trace:
>>  __dump_stack lib/dump_stack.c:16 [inline]
>>  dump_stack+0x292/0x398 lib/dump_stack.c:52
>>  kasan_object_err+0x1c/0x70 mm/kasan/report.c:164
>>  print_address_description mm/kasan/report.c:202 [inline]
>>  kasan_report_error mm/kasan/report.c:291 [inline]
>>  kasan_report+0x252/0x510 mm/kasan/report.c:347
>>  __asan_report_load4_noabort+0x14/0x20 mm/kasan/report.c:367
>>  ip_select_ttl include/net/dst.h:176 [inline]
>
> Probably same as the one you reported on ipv4_mtu(), it would
> be nice if you could test the patch I proposed:
>
> https://patchwork.ozlabs.org/patch/747556/

Applied your patch.

The bug gets triggered very rarely (only twice so far), but I'll let
you know if I see it again.

Thanks!

>
>
> Thanks!
>
>>  ip_queue_xmit+0x1817/0x1a30 net/ipv4/ip_output.c:485
>>  sctp_v4_xmit+0x10d/0x140 net/sctp/protocol.c:994
>>  sctp_packet_transmit+0x215c/0x3560 net/sctp/output.c:637
>>  sctp_outq_flush+0xade/0x3f90 net/sctp/outqueue.c:885
>>  sctp_outq_uncork+0x5a/0x70 net/sctp/outqueue.c:750
>>  sctp_cmd_interpreter net/sctp/sm_sideeffect.c:1773 [inline]
>>  sctp_side_effects net/sctp/sm_sideeffect.c:1175 [inline]
>>  sctp_do_sm+0x5a0/0x6a50 net/sctp/sm_sideeffect.c:1147
>>  sctp_primitive_ASSOCIATE+0x9d/0xd0 net/sctp/primitive.c:88
>>  sctp_sendmsg+0x270d/0x3b50 net/sctp/socket.c:1954
>>  inet_sendmsg+0x164/0x5b0 net/ipv4/af_inet.c:762
>>  sock_sendmsg_nosec net/socket.c:633 [inline]
>>  sock_sendmsg+0xca/0x110 net/socket.c:643
>>  SYSC_sendto+0x660/0x810 net/socket.c:1696
>>  SyS_sendto+0x40/0x50 net/socket.c:1664
>>  entry_SYSCALL_64_fastpath+0x1f/0xc2
>> RIP: 0033:0x4458d9
>> RSP: 002b:00007fdceca85b58 EFLAGS: 00000282 ORIG_RAX: 000000000000002c
>> RAX: ffffffffffffffda RBX: 0000000000000016 RCX: 00000000004458d9
>> RDX: 0000000000000087 RSI: 0000000020003000 RDI: 0000000000000016
>> RBP: 00000000006e2fe0 R08: 0000000020003000 R09: 0000000000000010
>> R10: 0000000000040841 R11: 0000000000000282 R12: 00000000007080a8
>> R13: 000000000000000a R14: 0000000000000005 R15: 0000000000000084
>> Object at ffff88006ab36008, in cache kmalloc-64 size: 64
>> Allocated:
>> PID = 7243
>>  save_stack_trace+0x16/0x20 arch/x86/kernel/stacktrace.c:59
>>  save_stack+0x43/0xd0 mm/kasan/kasan.c:513
>>  set_track mm/kasan/kasan.c:525 [inline]
>>  kasan_kmalloc+0xad/0xe0 mm/kasan/kasan.c:616
>>  kmem_cache_alloc_trace+0x82/0x270 mm/slub.c:2745
>>  kmalloc include/linux/slab.h:490 [inline]
>>  kzalloc include/linux/slab.h:663 [inline]
>>  fib_create_info+0x8e0/0x3a30 net/ipv4/fib_semantics.c:1040
>>  fib_table_insert+0x1a5/0x1550 net/ipv4/fib_trie.c:1221
>>  ip_rt_ioctl+0xddc/0x1590 net/ipv4/fib_frontend.c:597
>>  inet_ioctl+0xf2/0x1c0 net/ipv4/af_inet.c:882
>>  sock_do_ioctl+0x65/0xb0 net/socket.c:906
>>  sock_ioctl+0x28f/0x440 net/socket.c:1004
>>  vfs_ioctl fs/ioctl.c:45 [inline]
>>  do_vfs_ioctl+0x1bf/0x1780 fs/ioctl.c:685
>>  SYSC_ioctl fs/ioctl.c:700 [inline]
>>  SyS_ioctl+0x8f/0xc0 fs/ioctl.c:691
>>  entry_SYSCALL_64_fastpath+0x1f/0xc2
>> Freed:
>> PID = 12622
>>  save_stack_trace+0x16/0x20 arch/x86/kernel/stacktrace.c:59
>>  save_stack+0x43/0xd0 mm/kasan/kasan.c:513
>>  set_track mm/kasan/kasan.c:525 [inline]
>>  kasan_slab_free+0x73/0xc0 mm/kasan/kasan.c:589
>>  slab_free_hook mm/slub.c:1357 [inline]
>>  slab_free_freelist_hook mm/slub.c:1379 [inline]
>>  slab_free mm/slub.c:2961 [inline]
>>  kfree+0xe8/0x2b0 mm/slub.c:3882
>>  free_fib_info_rcu+0x4ba/0x5e0 net/ipv4/fib_semantics.c:218
>>  __rcu_reclaim kernel/rcu/rcu.h:118 [inline]
>>  rcu_do_batch.isra.64+0x947/0xcc0 kernel/rcu/tree.c:2879
>>  invoke_rcu_callbacks kernel/rcu/tree.c:3142 [inline]
>>  __rcu_process_callbacks kernel/rcu/tree.c:3109 [inline]
>>  rcu_process_callbacks+0x2cc/0xb90 kernel/rcu/tree.c:3126
>>  __do_softirq+0x2fb/0xb7d kernel/softirq.c:284
>> Memory state around the buggy address:
>>  ffff88006ab35f00: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
>>  ffff88006ab35f80: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
>>>ffff88006ab36000: fc fb fb fb fb fb fb fb fb fc fc fc fc fc fc fc
>>                                   ^
>>  ffff88006ab36080: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
>>  ffff88006ab36100: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
>> ==================================================================
>
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