Daniel J Blueman [off-list ref] wrote:

[ CC nf-devel, pablo ]

quoted

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.

Does this patch help?

Subject: [PATCH nf] netfilter: use skb_to_full_sk in ip_route_me_harder

inet_sk(skb->sk) is illegal in case skb is attached to request socket.

Fixes: ca6fb0651883 ("tcp: attach SYNACK messages to request sockets instead of listener")
Reported by: Daniel J Blueman [off-list ref]
Signed-off-by: Florian Westphal <fw@strlen.de>
---
 net/ipv4/netfilter.c | 7 ++++---
 1 file changed, 4 insertions(+), 3 deletions(-)

diff --git a/net/ipv4/netfilter.c b/net/ipv4/netfilter.c
index b3cc1335adbc..c0cc6aa8cfaa 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;
+       const struct sock *sk = skb_to_full_sk(skb);
+       __u8 flags = 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);