Re: [4.9.10] ip_route_me_harder() reading off-slab

[Eric Dumazet]

On Fri, 2017-02-17 at 12:36 +0800, Daniel J Blueman wrote:
> When booting a VM in libvirt/KVM attached to a local bridge and KASAN
> enabled on 4.9.10, we see a stream of KASAN warnings about off-slab
> access [1].
> 
> Let me know if you'd like more debug.

Could you try the following patch ?

Thanks !

diff --git a/net/ipv4/netfilter.c b/net/ipv4/netfilter.c
index 
b3cc1335adbc1a20dcd225d0501b0a286d27e3c8..18839e59da849f0988924bcbc9873965a3681eb0
 100644
--- a/net/ipv4/netfilter.c
+++ b/net/ipv4/netfilter.c
@@ -23,7 +23,8 @@ int ip_route_me_harder(struct net *net, struct sk_buff *skb, 
unsigned int addr_t
        struct rtable *rt;
        struct flowi4 fl4 = {};
        __be32 saddr = iph->saddr;
-       __u8 flags = skb->sk ? inet_sk_flowi_flags(skb->sk) : 0;
+       struct sock *sk = skb->sk;
+       __u8 flags = sk && sk_fullsock(sk) ? inet_sk_flowi_flags(sk) : 0;
        struct net_device *dev = skb_dst(skb)->dev;
        unsigned int hh_len;
 
@@ -40,7 +41,7 @@ int ip_route_me_harder(struct net *net, struct sk_buff *skb, 
unsigned int addr_t
        fl4.daddr = iph->daddr;
        fl4.saddr = saddr;
        fl4.flowi4_tos = RT_TOS(iph->tos);
-       fl4.flowi4_oif = skb->sk ? skb->sk->sk_bound_dev_if : 0;
+       fl4.flowi4_oif = sk ? sk->sk_bound_dev_if : 0;
        if (!fl4.flowi4_oif)
                fl4.flowi4_oif = l3mdev_master_ifindex(dev);
        fl4.flowi4_mark = skb->mark;
@@ -61,7 +62,7 @@ int ip_route_me_harder(struct net *net, struct sk_buff *skb, 
unsigned int addr_t
            xfrm_decode_session(skb, flowi4_to_flowi(&fl4), AF_INET) == 0) {
                struct dst_entry *dst = skb_dst(skb);
                skb_dst_set(skb, NULL);
-               dst = xfrm_lookup(net, dst, flowi4_to_flowi(&fl4), skb->sk, 0);
+               dst = xfrm_lookup(net, dst, flowi4_to_flowi(&fl4), sk, 0);
                if (IS_ERR(dst))
                        return PTR_ERR(dst);
                skb_dst_set(skb, dst);