Re: [PATCH] ip6mr: Fix skb_under_panic in ip6mr_cache_report()

[Simon Horman]

On Fri, Jul 28, 2023 at 06:00:35PM +0800, Yue Haibing wrote:
>  skbuff: skb_under_panic: text:ffffffff88771f69 len:56 put:-4
>  head:ffff88805f86a800 data:ffff887f5f86a850 tail:0x88 end:0x2c0 dev:pim6reg
>  ------------[ cut here ]------------
>  kernel BUG at net/core/skbuff.c:192!
>  invalid opcode: 0000 [#1] PREEMPT SMP KASAN
>  CPU: 2 PID: 22968 Comm: kworker/2:11 Not tainted 6.5.0-rc3-00044-g0a8db05b571a #236
>  Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.15.0-1 04/01/2014
>  Workqueue: ipv6_addrconf addrconf_dad_work
>  RIP: 0010:skb_panic+0x152/0x1d0
>  Call Trace:
>   <TASK>
>   skb_push+0xc4/0xe0
>   ip6mr_cache_report+0xd69/0x19b0
>   reg_vif_xmit+0x406/0x690
>   dev_hard_start_xmit+0x17e/0x6e0
>   __dev_queue_xmit+0x2d6a/0x3d20
>   vlan_dev_hard_start_xmit+0x3ab/0x5c0
>   dev_hard_start_xmit+0x17e/0x6e0
>   __dev_queue_xmit+0x2d6a/0x3d20
>   neigh_connected_output+0x3ed/0x570
>   ip6_finish_output2+0x5b5/0x1950
>   ip6_finish_output+0x693/0x11c0
>   ip6_output+0x24b/0x880
>   NF_HOOK.constprop.0+0xfd/0x530
>   ndisc_send_skb+0x9db/0x1400
>   ndisc_send_rs+0x12a/0x6c0
>   addrconf_dad_completed+0x3c9/0xea0
>   addrconf_dad_work+0x849/0x1420
>   process_one_work+0xa22/0x16e0
>   worker_thread+0x679/0x10c0
>   ret_from_fork+0x28/0x60
>   ret_from_fork_asm+0x11/0x20
> 
> When setup a vlan device on dev pim6reg, DAD ns packet may sent on reg_vif_xmit().
> reg_vif_xmit()
>     ip6mr_cache_report()
>         skb_push(skb, -skb_network_offset(pkt));//skb_network_offset(pkt) is 4
> And skb_push declar as this:

nit: declar as this -> declared as

> 	void *skb_push(struct sk_buff *skb, unsigned int len);
> 		skb->data -= len;
> 		//0xffff888f5f86a84c - 0xfffffffc = 0xffff887f5f86a850
> skb->data is set to 0xffff887f5f86a850, which is invalid mem addr, lead to skb_push() fails.
> 
> Fixes: 14fb64e1f449 ("[IPV6] MROUTE: Support PIM-SM (SSM).")
> Signed-off-by: Yue Haibing <yuehaibing@xxxxxxxxxx>

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