netdev - Re: [PATCH v2 net] icmp6: Fix null-ptr-deref of ip6_null_entry->rt6i_idev in icmp6

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Date: Sat, 8 Jul 2023 09:35:27 +0800
From: YueHaibing <yuehaibing@...wei.com>
To: Kuniyuki Iwashima <kuniyu@...zon.com>, "David S. Miller"
	<davem@...emloft.net>, David Ahern <dsahern@...nel.org>, Eric Dumazet
	<edumazet@...gle.com>, Jakub Kicinski <kuba@...nel.org>, Paolo Abeni
	<pabeni@...hat.com>
CC: Kuniyuki Iwashima <kuni1840@...il.com>, <netdev@...r.kernel.org>, Wang
 Yufen <wangyufen@...wei.com>
Subject: Re: [PATCH v2 net] icmp6: Fix null-ptr-deref of
 ip6_null_entry->rt6i_idev in icmp6_dev().

On 2023/7/8 8:21, Kuniyuki Iwashima wrote:
> With some IPv6 Ext Hdr (RPL, SRv6, etc.), we can send a packet that
> has the link-local address as src and dst IP and will be forwarded to
> an external IP in the IPv6 Ext Hdr.
> 
> For example, the script below generates a SRv6 packet whose src IP is
> the link-local address and dst is updated to 11::.
> 
>   # for f in $(find /proc/sys/net/ -name *seg6_enabled*); do echo 1 > $f; done
>   # python3
>   >>> from socket import *
>   >>> from scapy.all import *
>   >>>
>   >>> SRC_ADDR = DST_ADDR = "fe80::5054:ff:fe12:3456"
>   >>>
>   >>> pkt = IPv6(src=SRC_ADDR, dst=DST_ADDR)
>   >>> pkt /= IPv6ExtHdrSegmentRouting(type=4, addresses=["11::", "22::"], segleft=1)
>   >>>
>   >>> sk = socket(AF_INET6, SOCK_RAW, IPPROTO_RAW)
>   >>> sk.sendto(bytes(pkt), (DST_ADDR, 0))
> 
> For such a packet, we call ip6_route_input() to look up a route for the
> next destination in these three functions depending on the header type.
> 
>   * ipv6_rthdr_rcv()
>   * ipv6_rpl_srh_rcv()
>   * ipv6_srh_rcv()
> 
> If no route is found, ip6_null_entry is set to skb, and the following
> dst_input(skb) calls ip6_pkt_drop().
> 
> Finally, in icmp6_dev(), we dereference skb_rt6_info(skb)->rt6i_idev->dev
> as the input device is the loopback interface.  Then, we have to check if
> skb_rt6_info(skb)->rt6i_idev is NULL or not to avoid NULL pointer deref
> for ip6_null_entry.
> 
...

> Fixes: 4832c30d5458 ("net: ipv6: put host and anycast routes on device with address")
> Reported-by: Wang Yufen <wangyufen@...wei.com>

> Closes: https://lore.kernel.org/netdev/1ddf7fc8-bcb3-ab48-4894-24158e8a9d0f@huawei.com/

This link seems not right.

> Signed-off-by: Kuniyuki Iwashima <kuniyu@...zon.com>
> Reviewed-by: David Ahern <dsahern@...nel.org>
> ---
> v2:
>   * Add Reviewed-by
>   * s/fib6_null_entry/ip6_null_entry/
> 
> v1: https://lore.kernel.org/netdev/20230706233024.63730-1-kuniyu@amazon.com/
> ---
>  net/ipv6/icmp.c | 5 ++++-
>  1 file changed, 4 insertions(+), 1 deletion(-)
> 
> diff --git a/net/ipv6/icmp.c b/net/ipv6/icmp.c
> index 9edf1f45b1ed..65fa5014bc85 100644
> --- a/net/ipv6/icmp.c
> +++ b/net/ipv6/icmp.c
> @@ -424,7 +424,10 @@ static struct net_device *icmp6_dev(const struct sk_buff *skb)
>  	if (unlikely(dev->ifindex == LOOPBACK_IFINDEX || netif_is_l3_master(skb->dev))) {
>  		const struct rt6_info *rt6 = skb_rt6_info(skb);
>  
> -		if (rt6)
> +		/* The destination could be an external IP in Ext Hdr (SRv6, RPL, etc.),
> +		 * and ip6_null_entry could be set to skb if no route is found.
> +		 */
> +		if (rt6 && rt6->rt6i_idev)
>  			dev = rt6->rt6i_idev->dev;
>  	}
>  
>