Re: Subject: [PATCH netfilter] ipvs: Fix crash when ipv6 route unreach

From: hujunwei
Date: Tue May 07 2019 - 11:42:34 EST

On 2019/5/7 15:45, Julian Anastasov wrote:
> Hello,
> On Tue, 7 May 2019, hujunwei wrote:
>> From: Junwei Hu <hujunwei4@xxxxxxxxxx>
>> When Tcp send RST packet in ipvs, crash occurs with the following
>> stack trace:
>> BUG: unable to handle kernel NULL pointer dereference at 0000000000000018
>> PID: 0 COMMAND: "swapper/2"
>> TASK: ffff9ec83889bf40 (1 of 4) [THREAD_INFO: ffff9ec8388b0000]
>> [exception RIP: __ip_vs_get_out_rt_v6+1250]
>> RIP: ffffffffc0d566f2 RSP: ffff9ec83ed03c68 RFLAGS: 00010246
>> RAX: 0000000000000000 RBX: ffff9ec835e85000 RCX: 000000000005e1f9
>> RDX: 000000000005e1f8 RSI: 0000000000000200 RDI: ffff9ec83e801b00
>> RBP: ffff9ec83ed03cd8 R8: 000000000001bb40 R9: ffffffffc0d5673f
>> R10: ffff9ec83ed1bb40 R11: ffffe2d384d4fdc0 R12: ffff9ec7b7ad5900
>> R13: 0000000000000000 R14: 0000000000000007 R15: ffff9ec8353f7580
>> ORIG_RAX: ffffffffffffffff CS: 0010 SS: 0018
>> [ffff9ec83ed03ce0] ip_vs_fnat_xmit_v6 at ffffffffc0d5b42c [ip_vs]
>> [ffff9ec83ed03d70] tcp_send_rst_ipv6 at ffffffffc0d6542a [ip_vs]
>> [ffff9ec83ed03df8] tcp_conn_expire_handler at ffffffffc0d65823 [ip_vs]
>> [ffff9ec83ed03e20] ip_vs_conn_expire at ffffffffc0d42373 [ip_vs]
>> [ffff9ec83ed03e70] call_timer_fn at ffffffffae0a6b58
>> [ffff9ec83ed03ea8] run_timer_softirq at ffffffffae0a904d
>> [ffff9ec83ed03f20] __do_softirq at ffffffffae09fa85
>> [ffff9ec83ed03f90] call_softirq at ffffffffae739dac
>> [ffff9ec83ed03fa8] do_softirq at ffffffffae02e62b
>> [ffff9ec83ed03fc0] irq_exit at ffffffffae09fe25
>> [ffff9ec83ed03fd8] smp_apic_timer_interrupt at ffffffffae73b158
>> [ffff9ec83ed03ff0] apic_timer_interrupt at ffffffffae737872
>> TCP connection timeout and send a RST packet, the skb is alloc
>> by alloc_skb, the pointer skb->dev and skb_dst(skb) is NULL,
>> however, ipv6 route unreach at that time, so go into err_unreach.
>> In err_unreach, crash occurs when skb->dev and skb_dst(skb) is NULL.
> I guess, this is a modified IPVS module and the problem
> can not occur in mainline kernel. ip_vs_in() and ip_vs_out() already
> have check for skb_dst(). May be you generate skb without attached
> route, so skb_dst is NULL. Also, note that decrement_ttl() has similar
> code.

Hi Julian, thank you for replay.
We are developing based on IPVS module. That code seems less compatible,
i think it is meaningful to make the code robust.
All above just my advice.