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 ]---