From 51210ad5a558dcc7511d0c083f5cd796077b4e4d Mon Sep 17 00:00:00 2001 From: Florian Westphal Date: Tue, 29 Oct 2019 01:44:04 +0100 Subject: inet: do not call sublist_rcv on empty list 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 Reported-by: syzbot+c54f457cad330e57e967@syzkaller.appspotmail.com Fixes: ca58fbe06c54 ("netfilter: add and use nf_hook_slow_list()") Signed-off-by: Florian Westphal Tested-by: Leon Romanovsky Tested-by: Nikolay Aleksandrov Signed-off-by: David S. Miller --- net/ipv6/ip6_input.c | 3 ++- 1 file changed, 2 insertions(+), 1 deletion(-) (limited to 'net/ipv6/ip6_input.c') diff --git a/net/ipv6/ip6_input.c b/net/ipv6/ip6_input.c index 3d71c7d6102c..ef7f707d9ae3 100644 --- a/net/ipv6/ip6_input.c +++ b/net/ipv6/ip6_input.c @@ -325,7 +325,8 @@ void ipv6_list_rcv(struct list_head *head, struct packet_type *pt, list_add_tail(&skb->list, &sublist); } /* dispatch final sublist */ - ip6_sublist_rcv(&sublist, curr_dev, curr_net); + if (!list_empty(&sublist)) + ip6_sublist_rcv(&sublist, curr_dev, curr_net); } INDIRECT_CALLABLE_DECLARE(int udpv6_rcv(struct sk_buff *)); -- cgit