netdev - Re: [PATCH net-next] inet: do not call sublist

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Date:   Tue, 29 Oct 2019 15:35:17 +0200
From:   Nikolay Aleksandrov <nikolay@...ulusnetworks.com>
To:     Florian Westphal <fw@...len.de>, netdev@...r.kernel.org
Cc:     syzbot+c54f457cad330e57e967@...kaller.appspotmail.com,
        syzkaller-bugs@...glegroups.com, netfilter-devel@...r.kernel.org,
        Edward Cree <ecree@...arflare.com>
Subject: Re: [PATCH net-next] inet: do not call sublist_rcv on empty list

On 29/10/2019 02:44, Florian Westphal wrote:
> syzbot triggered struct net NULL deref in NF_HOOK_LIST:
> RIP: 0010:NF_HOOK_LIST include/linux/netfilter.h:331 [inline]
> RIP: 0010:ip6_sublist_rcv+0x5c9/0x930 net/ipv6/ip6_input.c:292
>  ipv6_list_rcv+0x373/0x4b0 net/ipv6/ip6_input.c:328
>  __netif_receive_skb_list_ptype net/core/dev.c:5274 [inline]
> 
> Reason:
> void ipv6_list_rcv(struct list_head *head, struct packet_type *pt,
>                    struct net_device *orig_dev)
> [..]
>         list_for_each_entry_safe(skb, next, head, list) {
> 		/* iterates list */
>                 skb = ip6_rcv_core(skb, dev, net);
> 		/* ip6_rcv_core drops skb -> NULL is returned */
>                 if (skb == NULL)
>                         continue;
> 	[..]
> 	}
> 	/* sublist is empty -> curr_net is NULL */
>         ip6_sublist_rcv(&sublist, curr_dev, curr_net);
> 
> Before the recent change NF_HOOK_LIST did a list iteration before
> struct net deref, i.e. it was a no-op in the empty list case.
> 
> List iteration now happens after *net deref, causing crash.
> 
> Follow the same pattern as the ip(v6)_list_rcv loop and add a list_empty
> test for the final sublist dispatch too.
> 
> Cc: Edward Cree <ecree@...arflare.com>
> Reported-by: syzbot+c54f457cad330e57e967@...kaller.appspotmail.com
> Fixes: ca58fbe06c54 ("netfilter: add and use nf_hook_slow_list()")
> Signed-off-by: Florian Westphal <fw@...len.de>
> ---
>  net/ipv4/ip_input.c  | 3 ++-
>  net/ipv6/ip6_input.c | 3 ++-
>  2 files changed, 4 insertions(+), 2 deletions(-)
> 

Fixed my boot problem as well.

Tested-by: Nikolay Aleksandrov <nikolay@...ulusnetworks.com>