Re: [PATCH v2 net] icmp6: Fix null-ptr-deref of ip6_null_entry->rt6i_idev in icmp6_dev().

[Kuniyuki Iwashima <kuniyu@amazon.com>]

From: YueHaibing <yuehaibing@huawei.com>
Date: Sat, 8 Jul 2023 09:35:27 +0800
> 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@huawei.com>
> 
> > Closes: https://lore.kernel.org/netdev/1ddf7fc8-bcb3-ab48-4894-24158e8a9d0f@huawei.com/
> 
> This link seems not right.

Ah... exactly.
I'll fix it up in v3.
https://lore.kernel.org/netdev/c41403a9-c2f6-3b7e-0c96-e1901e605cd0@huawei.com/

Thanks!

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