Re: KASAN: slab-out-of-bounds Read in _decode_session6

[Dmitry Vyukov]

On Sun, Sep 2, 2018 at 6:41 AM, syzbot
<syzbot+acffccec848dc13fe459@xxxxxxxxxxxxxxxxxxxxxxxxx> wrote:
> Hello,
>
> syzbot found the following crash on:
>
> HEAD commit:    93ee30f3e8b4 xsk: i40e: get rid of useless struct xdp_umem..
> git tree:       bpf-next
> console output: https://syzkaller.appspot.com/x/log.txt?x=11f2115a400000
> kernel config:  https://syzkaller.appspot.com/x/.config?x=531a917630d2a492
> dashboard link: https://syzkaller.appspot.com/bug?extid=acffccec848dc13fe459
> compiler:       gcc (GCC) 8.0.1 20180413 (experimental)
> syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=116b3492400000

Potentially this is bpf-related because the repro just runs a bpf
program. +bpf maintainers.


> IMPORTANT: if you fix the bug, please add the following tag to the commit:
> Reported-by: syzbot+acffccec848dc13fe459@xxxxxxxxxxxxxxxxxxxxxxxxx
>
> 8021q: adding VLAN 0 to HW filter on device team0
> 8021q: adding VLAN 0 to HW filter on device team0
> 8021q: adding VLAN 0 to HW filter on device team0
> 8021q: adding VLAN 0 to HW filter on device team0
> ==================================================================
> BUG: KASAN: slab-out-of-bounds in _decode_session6+0x1331/0x14e0
> net/ipv6/xfrm6_policy.c:161
> Read of size 1 at addr ffff8801d882eec7 by task syz-executor1/6667
>
> CPU: 0 PID: 6667 Comm: syz-executor1 Not tainted 4.19.0-rc1+ #86
> 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+0x1c9/0x2b4 lib/dump_stack.c:113
>  print_address_description+0x6c/0x20b mm/kasan/report.c:256
>  kasan_report_error mm/kasan/report.c:354 [inline]
>  kasan_report.cold.7+0x242/0x30d mm/kasan/report.c:412
>  __asan_report_load1_noabort+0x14/0x20 mm/kasan/report.c:430
>  _decode_session6+0x1331/0x14e0 net/ipv6/xfrm6_policy.c:161
>  __xfrm_decode_session+0x71/0x140 net/xfrm/xfrm_policy.c:2299
>  xfrm_decode_session include/net/xfrm.h:1232 [inline]
>  vti6_tnl_xmit+0x3c3/0x1bc1 net/ipv6/ip6_vti.c:542
>  __netdev_start_xmit include/linux/netdevice.h:4313 [inline]
>  netdev_start_xmit include/linux/netdevice.h:4322 [inline]
>  xmit_one net/core/dev.c:3217 [inline]
>  dev_hard_start_xmit+0x272/0xc10 net/core/dev.c:3233
>  __dev_queue_xmit+0x2ab2/0x3870 net/core/dev.c:3803
>  dev_queue_xmit+0x17/0x20 net/core/dev.c:3836
>  __bpf_tx_skb net/core/filter.c:2012 [inline]
>  __bpf_redirect_common net/core/filter.c:2050 [inline]
>  __bpf_redirect+0x5b7/0xae0 net/core/filter.c:2057
>  ____bpf_clone_redirect net/core/filter.c:2090 [inline]
>  bpf_clone_redirect+0x2f6/0x490 net/core/filter.c:2062
>  bpf_prog_c39d1ba309a769f7+0x749/0x1000
>
> Allocated by task 6667:
>  save_stack+0x43/0xd0 mm/kasan/kasan.c:448
>  set_track mm/kasan/kasan.c:460 [inline]
>  kasan_kmalloc+0xc4/0xe0 mm/kasan/kasan.c:553
>  __do_kmalloc_node mm/slab.c:3682 [inline]
>  __kmalloc_node_track_caller+0x47/0x70 mm/slab.c:3696
>  __kmalloc_reserve.isra.41+0x3a/0xe0 net/core/skbuff.c:137
>  pskb_expand_head+0x230/0x10e0 net/core/skbuff.c:1463
>  skb_ensure_writable+0x3dd/0x640 net/core/skbuff.c:5129
>  __bpf_try_make_writable net/core/filter.c:1633 [inline]
>  bpf_try_make_writable net/core/filter.c:1639 [inline]
>  bpf_try_make_head_writable net/core/filter.c:1647 [inline]
>  ____bpf_clone_redirect net/core/filter.c:2084 [inline]
>  bpf_clone_redirect+0x14a/0x490 net/core/filter.c:2062
>  bpf_prog_c39d1ba309a769f7+0x749/0x1000
>
> Freed by task 5493:
>  save_stack+0x43/0xd0 mm/kasan/kasan.c:448
>  set_track mm/kasan/kasan.c:460 [inline]
>  __kasan_slab_free+0x11a/0x170 mm/kasan/kasan.c:521
>  kasan_slab_free+0xe/0x10 mm/kasan/kasan.c:528
>  __cache_free mm/slab.c:3498 [inline]
>  kfree+0xd9/0x210 mm/slab.c:3813
>  skb_free_head+0x99/0xc0 net/core/skbuff.c:550
>  skb_release_data+0x6a4/0x880 net/core/skbuff.c:570
>  skb_release_all+0x4a/0x60 net/core/skbuff.c:627
>  __kfree_skb net/core/skbuff.c:641 [inline]
>  consume_skb+0x190/0x4e0 net/core/skbuff.c:701
>  netlink_dump+0xb14/0xd50 net/netlink/af_netlink.c:2269
>  netlink_recvmsg+0xf84/0x1490 net/netlink/af_netlink.c:1991
>  sock_recvmsg_nosec net/socket.c:794 [inline]
>  sock_recvmsg+0xd0/0x110 net/socket.c:801
>  ___sys_recvmsg+0x2b6/0x680 net/socket.c:2276
>  __sys_recvmsg+0x11a/0x290 net/socket.c:2325
>  __do_sys_recvmsg net/socket.c:2335 [inline]
>  __se_sys_recvmsg net/socket.c:2332 [inline]
>  __x64_sys_recvmsg+0x78/0xb0 net/socket.c:2332
>  do_syscall_64+0x1b9/0x820 arch/x86/entry/common.c:290
>  entry_SYSCALL_64_after_hwframe+0x49/0xbe
>
> The buggy address belongs to the object at ffff8801d882ecc0
>  which belongs to the cache kmalloc-512 of size 512
> The buggy address is located 7 bytes to the right of
>  512-byte region [ffff8801d882ecc0, ffff8801d882eec0)
> The buggy address belongs to the page:
> page:ffffea0007620b80 count:1 mapcount:0 mapping:ffff8801dac00940 index:0x0
> flags: 0x2fffc0000000100(slab)
> raw: 02fffc0000000100 ffffea00070fc048 ffffea00075f9c08 ffff8801dac00940
> raw: 0000000000000000 ffff8801d882e040 0000000100000006 0000000000000000
> page dumped because: kasan: bad access detected
>
> Memory state around the buggy address:
>  ffff8801d882ed80: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
>  ffff8801d882ee00: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
>>
>> ffff8801d882ee80: 00 00 00 00 00 00 00 00 fc fc fc fc fc fc fc fc
>
>                                            ^
>  ffff8801d882ef00: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
>  ffff8801d882ef80: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
> ==================================================================
>
>
> ---
> This bug is generated by a bot. It may contain errors.
> See https://goo.gl/tpsmEJ for more information about syzbot.
> syzbot engineers can be reached at syzkaller@xxxxxxxxxxxxxxxxx
>
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>
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