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@xxxxxxxxxxxxxx>
Reported-by: syzbot+c54f457cad330e57e967@xxxxxxxxxxxxxxxxxxxxxxxxx
Fixes: ca58fbe06c54 ("netfilter: add and use nf_hook_slow_list()")
Signed-off-by: Florian Westphal <fw@xxxxxxxxx>
---
net/ipv4/ip_input.c | 3 ++-
net/ipv6/ip6_input.c | 3 ++-
2 files changed, 4 insertions(+), 2 deletions(-)
diff --git a/net/ipv4/ip_input.c b/net/ipv4/ip_input.c
index c59a78a267c3..24a95126e698 100644
--- a/net/ipv4/ip_input.c
+++ b/net/ipv4/ip_input.c
@@ -611,5 +611,6 @@ void ip_list_rcv(struct list_head *head, struct packet_type *pt,
list_add_tail(&skb->list, &sublist);
}
/* dispatch final sublist */
- ip_sublist_rcv(&sublist, curr_dev, curr_net);
+ if (!list_empty(&sublist))
+ ip_sublist_rcv(&sublist, curr_dev, curr_net);
}
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 *));
--
2.23.0
