Re: v4.14-rc3/arm64 DABT exception in atomic_inc() / __skb_clone()

[Eric Dumazet]

On Thu, Oct 19, 2017 at 7:16 PM, Wei Wei <dotweiba@xxxxxxxxx> wrote:
> Hi all,
>
> I have fuzzed v4.14-rc3 using syzkaller and found a bug similar to that one [1].
> But the call trace isnât the same. The atomic_inc() might handle a corrupted
> skb_buff.
>
> The logs and config have been uploaded to my github repo [2].
>
> [1] https://lkml.org/lkml/2017/10/2/216
> [2] https://github.com/dotweiba/skb_clone_atomic_inc_bug
>
> Thanks,
> Wei
>
>  Unable to handle kernel paging request at virtual address ffff80005bfb81ed
>  Mem abort info:
>    Exception class = DABT (current EL), IL = 32 bits
>    SET = 0, FnV = 0
>    EA = 0, S1PTW = 0
>  Data abort info:
>    ISV = 0, ISS = 0x00000033
>    CM = 0, WnR = 0
>  swapper pgtable: 4k pages, 48-bit VAs, pgd = ffff20000b366000
>  [ffff80005bfb81ed] *pgd=00000000beff7003, *pud=00e8000080000711
>  Internal error: Oops: 96000021 [#1] PREEMPT SMP
>  Modules linked in:
>  CPU: 3 PID: 4725 Comm: syz-executor0 Not tainted 4.14.0-rc3 #3
>  Hardware name: linux,dummy-virt (DT)
>  task: ffff800074409e00 task.stack: ffff800033db0000
>  PC is at __skb_clone+0x430/0x5b0
>  LR is at __skb_clone+0x1dc/0x5b0
>  pc : [<ffff200009705f50>] lr : [<ffff200009705cfc>] pstate: 10000145
>  sp : ffff800033db33d0
>  x29: ffff800033db33d0 x28: ffff2000098ac378
>  x27: ffff100006a860e1 x26: 1ffff000067b66b6
>  x25: ffff8000743340a0 x24: ffff800035430708
>  x23: ffff80005bfb80c9 x22: ffff800035430710
>  x21: 0000000000000380 x20: ffff800035430640
>  x19: ffff8000354312c0 x18: 0000000000000000
>  x17: 00000000004af000 x16: ffff20000845e8c8
>  x15: 000000001e518060 x14: 0000ffffd8316070
>  x13: 0000ffffd8316090 x12: ffffffffffffffff
>  x11: 1ffff00006a8626f x10: ffff100006a8626f
>  x9 : dfff200000000000 x8 : 0082009000900608
>  x7 : 0000000000000000 x6 : ffff800035431380
>  x5 : ffff100006a86270 x4 : 0000000000000000
>  x3 : 1ffff00006a86273 x2 : 0000000000000000
>  x1 : 0000000000000100 x0 : ffff80005bfb81ed
>  Process syz-executor0 (pid: 4725, stack limit = 0xffff800033db0000)
>  Call trace:
>  Exception stack(0xffff800033db3290 to 0xffff800033db33d0)
>  3280:                                   ffff80005bfb81ed 0000000000000100
>  32a0: 0000000000000000 1ffff00006a86273 0000000000000000 ffff100006a86270
>  32c0: ffff800035431380 0000000000000000 0082009000900608 dfff200000000000
>  32e0: ffff100006a8626f 1ffff00006a8626f ffffffffffffffff 0000ffffd8316090
>  3300: 0000ffffd8316070 000000001e518060 ffff20000845e8c8 00000000004af000
>  3320: 0000000000000000 ffff8000354312c0 ffff800035430640 0000000000000380
>  3340: ffff800035430710 ffff80005bfb80c9 ffff800035430708 ffff8000743340a0
>  3360: 1ffff000067b66b6 ffff100006a860e1 ffff2000098ac378 ffff800033db33d0
>  3380: ffff200009705cfc ffff800033db33d0 ffff200009705f50 0000000010000145
>  33a0: ffff8000354312c0 ffff800035430640 0001000000000000 ffff800074334000
>  33c0: ffff800033db33d0 ffff200009705f50
>  [<ffff200009705f50>] __skb_clone+0x430/0x5b0
>  [<ffff20000971520c>] skb_clone+0x164/0x2c8
>  [<ffff2000098ac498>] arp_rcv+0x120/0x488
>  [<ffff200009741878>] __netif_receive_skb_core+0x11e8/0x18c8
>  [<ffff2000097479b0>] __netif_receive_skb+0x30/0x198
>  [<ffff200009751fd8>] netif_receive_skb_internal+0x98/0x370
>  [<ffff2000097522cc>] netif_receive_skb+0x1c/0x28
>  [<ffff2000090730e0>] tun_get_user+0x12f0/0x2e40
>  [<ffff200009074ddc>] tun_chr_write_iter+0xbc/0x140
>  [<ffff200008457284>] do_iter_readv_writev+0x2d4/0x468
>  [<ffff20000845a5a0>] do_iter_write+0x148/0x498
>  [<ffff20000845aac0>] vfs_writev+0x118/0x250
>  [<ffff20000845acbc>] do_writev+0xc4/0x1e8
>  [<ffff20000845e8fc>] SyS_writev+0x34/0x48
>  Exception stack(0xffff800033db3ec0 to 0xffff800033db4000)
>  3ec0: 0000000000000015 0000ffff829985e0 0000000000000001 0000ffff8299851c
>  3ee0: 0000ffff82999068 0000ffff82998f60 0000ffff82999650 0000000000000000
>  3f00: 0000000000000042 0000000000000036 0000000000406608 0000ffff82998400
>  3f20: 0000ffff82998f60 0000ffffd8316090 0000ffffd8316070 000000001e518060
>  3f40: 0000000000000000 00000000004af000 0000000000000000 0000000000000036
>  3f60: 0000000020004fca 0000000020000000 000000000046ccf0 0000000000000530
>  3f80: 000000000046cce8 00000000004ade98 0000000000000000 00000000395fa6f0
>  3fa0: 0000ffff82998f60 0000ffff82998560 0000000000431448 0000ffff82998520
>  3fc0: 000000000043145c 0000000080000000 0000000000000015 0000000000000042
>  3fe0: 0000000000000000 0000000000000000 0000000000000000 0000000000000000
>  [<ffff200008083ef0>] el0_svc_naked+0x24/0x28
>  Code: f9406680 8b010000 91009000 f9800011 (885f7c01)
>  ---[ end trace 261e7ac1458ccc0a ]---

Please provide proper file:line information in this trace.

You can use scripts/decode_stacktrace.sh

Thanks.