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

On Thu, Oct 19, 2017 at 8:13 PM, Wei Wei [off-list ref] wrote:

Sry. Here it is.

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 (/./arch/arm64/include/asm/atomic_ll_sc.h:113 (discriminator 4) /net/core/skbuff.c:873 (discriminator 4))
LR is at __skb_clone (/net/core/skbuff.c:861 (discriminator 4))
pc : lr : 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
__skb_clone (/./arch/arm64/include/asm/atomic_ll_sc.h:113 (discriminator 4) /net/core/skbuff.c:873 (discriminator 4))
skb_clone (/net/core/skbuff.c:1286)
arp_rcv (/./include/linux/skbuff.h:1518 /net/ipv4/arp.c:946)
__netif_receive_skb_core (/net/core/dev.c:1859 /net/core/dev.c:1874 /net/core/dev.c:4416)
__netif_receive_skb (/net/core/dev.c:4466)
netif_receive_skb_internal (/net/core/dev.c:4539)
netif_receive_skb (/net/core/dev.c:4564)
tun_get_user (/./include/linux/bottom_half.h:31 /drivers/net/tun.c:1219 /drivers/net/tun.c:1553)
tun_chr_write_iter (/drivers/net/tun.c:1579)
do_iter_readv_writev (/./include/linux/fs.h:1770 /fs/read_write.c:673)
do_iter_write (/fs/read_write.c:952)
vfs_writev (/fs/read_write.c:997)
do_writev (/fs/read_write.c:1032)
SyS_writev (/fs/read_write.c:1102)
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
el0_svc_naked (/arch/arm64/kernel/entry.S:853)
Code: f9406680 8b010000 91009000 f9800011 (885f7c01)
All code
========
   0:   80 66 40 f9             andb   $0xf9,0x40(%rsi)
   4:   00 00                   add    %al,(%rax)
   6:   01 8b 00 90 00 91       add    %ecx,-0x6eff7000(%rbx)
   c:   11 00                   adc    %eax,(%rax)
   e:   80 f9 01                cmp    $0x1,%cl
  11:   7c 5f                   jl     0x72
  13:*  88 00                   mov    %al,(%rax)               <-- trapping instruction
  15:   00 00                   add    %al,(%rax)
        ...

Code starting with the faulting instruction
===========================================
   0:   01 7c 5f 88             add    %edi,-0x78(%rdi,%rbx,2)
   4:   00 00                   add    %al,(%rax)
        ...
—[ end trace 261e7ac1458ccc0a ]---

I thought it was happening on arm64 ?

This is x86_64 disassembly :/

Thanks.

Thanks,
Wei

quoted

On 19 Oct 2017, at 10:53 PM, Eric Dumazet [off-list ref] wrote:

On Thu, Oct 19, 2017 at 7:16 PM, Wei Wei [off-list ref] wrote:

quoted

Hi all,

I have fuzzed v4.14-rc3 using syzkaller and found a bug similar to that one [1].
But the call trace isn’t 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.