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

[Wei Wei]

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 ]---