On Mon, Jan 15, 2024 at 9:57 PM Kuniyuki Iwashima <kuniyu@xxxxxxxxxx> wrote:
>
> We will support arbitrary SYN Cookie with BPF in the following
> patch.
>
> If BPF prog validates ACK and kfunc allocates a reqsk, it will
> be carried to cookie_[46]_check() as skb->sk. If skb->sk is not
> NULL, we call cookie_bpf_check().
>
> Then, we clear skb->sk and skb->destructor, which are needed not
> to hold refcnt for reqsk and the listener. See the following patch
> for details.
>
> After that, we finish initialisation for the remaining fields with
> cookie_tcp_reqsk_init().
>
> Note that the server side WScale is set only for non-BPF SYN Cookie.
So the difference between BPF and non-BPF is using a req->syncookie
which had a prior meaning ?
This is very confusing, and needs documentation/comments.
>
> Signed-off-by: Kuniyuki Iwashima <kuniyu@xxxxxxxxxx>
> ---
> include/net/tcp.h | 20 ++++++++++++++++++++
> net/ipv4/syncookies.c | 31 +++++++++++++++++++++++++++----
> net/ipv6/syncookies.c | 13 +++++++++----
> 3 files changed, 56 insertions(+), 8 deletions(-)
>
> diff --git a/include/net/tcp.h b/include/net/tcp.h
> index 114000e71a46..dfe99a084a71 100644
> --- a/include/net/tcp.h
> +++ b/include/net/tcp.h
> @@ -599,6 +599,26 @@ static inline bool cookie_ecn_ok(const struct net *net, const struct dst_entry *
> dst_feature(dst, RTAX_FEATURE_ECN);
> }
>
> +#if IS_ENABLED(CONFIG_BPF)
> +static inline bool cookie_bpf_ok(struct sk_buff *skb)
> +{
> + return skb->sk;
> +}
> +
> +struct request_sock *cookie_bpf_check(struct sock *sk, struct sk_buff *skb);
> +#else
> +static inline bool cookie_bpf_ok(struct sk_buff *skb)
> +{
> + return false;
> +}
> +
> +static inline struct request_sock *cookie_bpf_check(struct net *net, struct sock *sk,
> + struct sk_buff *skb)
> +{
> + return NULL;
> +}
> +#endif
> +
> /* From net/ipv6/syncookies.c */
> int __cookie_v6_check(const struct ipv6hdr *iph, const struct tcphdr *th);
> struct sock *cookie_v6_check(struct sock *sk, struct sk_buff *skb);
> diff --git a/net/ipv4/syncookies.c b/net/ipv4/syncookies.c
> index 981944c22820..be88bf586ff9 100644
> --- a/net/ipv4/syncookies.c
> +++ b/net/ipv4/syncookies.c
> @@ -295,6 +295,24 @@ static int cookie_tcp_reqsk_init(struct sock *sk, struct sk_buff *skb,
> return 0;
> }
>
> +#if IS_ENABLED(CONFIG_BPF)
> +struct request_sock *cookie_bpf_check(struct sock *sk, struct sk_buff *skb)
> +{
> + struct request_sock *req = inet_reqsk(skb->sk);
> +
> + skb->sk = NULL;
> + skb->destructor = NULL;
> +
> + if (cookie_tcp_reqsk_init(sk, skb, req)) {
> + reqsk_free(req);
> + req = NULL;
> + }
> +
> + return req;
> +}
> +EXPORT_SYMBOL_GPL(cookie_bpf_check);
> +#endif
> +
> struct request_sock *cookie_tcp_reqsk_alloc(const struct request_sock_ops *ops,
> struct sock *sk, struct sk_buff *skb,
> struct tcp_options_received *tcp_opt,
> @@ -395,9 +413,13 @@ struct sock *cookie_v4_check(struct sock *sk, struct sk_buff *skb)
> !th->ack || th->rst)
> goto out;
>
> - req = cookie_tcp_check(net, sk, skb);
> - if (IS_ERR(req))
> - goto out;
> + if (cookie_bpf_ok(skb)) {
> + req = cookie_bpf_check(sk, skb);
> + } else {
> + req = cookie_tcp_check(net, sk, skb);
> + if (IS_ERR(req))
> + goto out;
> + }
> if (!req)
> goto out_drop;
>
> @@ -445,7 +467,8 @@ struct sock *cookie_v4_check(struct sock *sk, struct sk_buff *skb)
> ireq->wscale_ok, &rcv_wscale,
> dst_metric(&rt->dst, RTAX_INITRWND));
>
> - ireq->rcv_wscale = rcv_wscale;
> + if (!req->syncookie)
> + ireq->rcv_wscale = rcv_wscale;
> ireq->ecn_ok &= cookie_ecn_ok(net, &rt->dst);
>
> ret = tcp_get_cookie_sock(sk, skb, req, &rt->dst);
> diff --git a/net/ipv6/syncookies.c b/net/ipv6/syncookies.c
> index c8d2ca27220c..6b9c69278819 100644
> --- a/net/ipv6/syncookies.c
> +++ b/net/ipv6/syncookies.c
> @@ -182,9 +182,13 @@ struct sock *cookie_v6_check(struct sock *sk, struct sk_buff *skb)
> !th->ack || th->rst)
> goto out;
>
> - req = cookie_tcp_check(net, sk, skb);
> - if (IS_ERR(req))
> - goto out;
> + if (cookie_bpf_ok(skb)) {
> + req = cookie_bpf_check(sk, skb);
> + } else {
> + req = cookie_tcp_check(net, sk, skb);
> + if (IS_ERR(req))
> + goto out;
> + }
> if (!req)
> goto out_drop;
>
> @@ -247,7 +251,8 @@ struct sock *cookie_v6_check(struct sock *sk, struct sk_buff *skb)
> ireq->wscale_ok, &rcv_wscale,
> dst_metric(dst, RTAX_INITRWND));
>
> - ireq->rcv_wscale = rcv_wscale;
> + if (!req->syncookie)
> + ireq->rcv_wscale = rcv_wscale;
I think a comment is deserved. I do not understand this.
cookie_v6_check() is dealing with syncookie, unless I am mistaken.
Also syzbot is not happy, req->syncookie might be uninitialized here.
BUG: KMSAN: uninit-value in cookie_v4_check+0x22b7/0x29e0
net/ipv4/syncookies.c:477
cookie_v4_check+0x22b7/0x29e0 net/ipv4/syncookies.c:477
tcp_v4_cookie_check net/ipv4/tcp_ipv4.c:1855 [inline]
tcp_v4_do_rcv+0xb17/0x10b0 net/ipv4/tcp_ipv4.c:1914
tcp_v4_rcv+0x4ce4/0x5420 net/ipv4/tcp_ipv4.c:2322
ip_protocol_deliver_rcu+0x2a3/0x13d0 net/ipv4/ip_input.c:205
ip_local_deliver_finish+0x332/0x500 net/ipv4/ip_input.c:233
NF_HOOK include/linux/netfilter.h:314 [inline]
ip_local_deliver+0x21f/0x490 net/ipv4/ip_input.c:254
dst_input include/net/dst.h:460 [inline]
ip_rcv_finish+0x4a2/0x520 net/ipv4/ip_input.c:449
NF_HOOK include/linux/netfilter.h:314 [inline]
ip_rcv+0xcd/0x380 net/ipv4/ip_input.c:569
__netif_receive_skb_one_core net/core/dev.c:5538 [inline]
__netif_receive_skb+0x319/0x9e0 net/core/dev.c:5652
process_backlog+0x480/0x8b0 net/core/dev.c:5981
__napi_poll+0xe7/0x980 net/core/dev.c:6632
napi_poll net/core/dev.c:6701 [inline]
net_rx_action+0x89d/0x1820 net/core/dev.c:6813
__do_softirq+0x1c0/0x7d7 kernel/softirq.c:554
do_softirq+0x9a/0x100 kernel/softirq.c:455
__local_bh_enable_ip+0x9f/0xb0 kernel/softirq.c:382
local_bh_enable include/linux/bottom_half.h:33 [inline]
rcu_read_unlock_bh include/linux/rcupdate.h:820 [inline]
__dev_queue_xmit+0x2776/0x52c0 net/core/dev.c:4362
dev_queue_xmit include/linux/netdevice.h:3091 [inline]
neigh_hh_output include/net/neighbour.h:526 [inline]
neigh_output include/net/neighbour.h:540 [inline]
ip_finish_output2+0x187a/0x1b70 net/ipv4/ip_output.c:235
__ip_finish_output+0x287/0x810
ip_finish_output+0x4b/0x550 net/ipv4/ip_output.c:323
NF_HOOK_COND include/linux/netfilter.h:303 [inline]
ip_output+0x15f/0x3f0 net/ipv4/ip_output.c:433
dst_output include/net/dst.h:450 [inline]
ip_local_out net/ipv4/ip_output.c:129 [inline]
__ip_queue_xmit+0x1e93/0x2030 net/ipv4/ip_output.c:535
ip_queue_xmit+0x60/0x80 net/ipv4/ip_output.c:549
__tcp_transmit_skb+0x3c70/0x4890 net/ipv4/tcp_output.c:1462
tcp_transmit_skb net/ipv4/tcp_output.c:1480 [inline]
tcp_write_xmit+0x3ee1/0x8900 net/ipv4/tcp_output.c:2792
__tcp_push_pending_frames net/ipv4/tcp_output.c:2977 [inline]
tcp_send_fin+0xa90/0x12e0 net/ipv4/tcp_output.c:3578
tcp_shutdown+0x198/0x1f0 net/ipv4/tcp.c:2716
inet_shutdown+0x33f/0x5b0 net/ipv4/af_inet.c:923
__sys_shutdown_sock net/socket.c:2425 [inline]
__sys_shutdown net/socket.c:2437 [inline]
__do_sys_shutdown net/socket.c:2445 [inline]
__se_sys_shutdown+0x2a4/0x440 net/socket.c:2443
__x64_sys_shutdown+0x6c/0xa0 net/socket.c:2443
do_syscall_64+0xd5/0x1f0
entry_SYSCALL_64_after_hwframe+0x6d/0x75
Uninit was stored to memory at:
reqsk_alloc include/net/request_sock.h:148 [inline]
inet_reqsk_alloc+0x651/0x7a0 net/ipv4/tcp_input.c:6978
cookie_tcp_reqsk_alloc+0xd4/0x900 net/ipv4/syncookies.c:328
cookie_tcp_check net/ipv4/syncookies.c:388 [inline]
cookie_v4_check+0x289f/0x29e0 net/ipv4/syncookies.c:420
tcp_v4_cookie_check net/ipv4/tcp_ipv4.c:1855 [inline]
tcp_v4_do_rcv+0xb17/0x10b0 net/ipv4/tcp_ipv4.c:1914
tcp_v4_rcv+0x4ce4/0x5420 net/ipv4/tcp_ipv4.c:2322
ip_protocol_deliver_rcu+0x2a3/0x13d0 net/ipv4/ip_input.c:205
ip_local_deliver_finish+0x332/0x500 net/ipv4/ip_input.c:233
NF_HOOK include/linux/netfilter.h:314 [inline]
ip_local_deliver+0x21f/0x490 net/ipv4/ip_input.c:254
dst_input include/net/dst.h:460 [inline]
ip_rcv_finish+0x4a2/0x520 net/ipv4/ip_input.c:449
NF_HOOK include/linux/netfilter.h:314 [inline]
ip_rcv+0xcd/0x380 net/ipv4/ip_input.c:569
__netif_receive_skb_one_core net/core/dev.c:5538 [inline]
__netif_receive_skb+0x319/0x9e0 net/core/dev.c:5652
process_backlog+0x480/0x8b0 net/core/dev.c:5981
__napi_poll+0xe7/0x980 net/core/dev.c:6632
napi_poll net/core/dev.c:6701 [inline]
net_rx_action+0x89d/0x1820 net/core/dev.c:6813
__do_softirq+0x1c0/0x7d7 kernel/softirq.c:554
Uninit was created at:
__alloc_pages+0x9a7/0xe00 mm/page_alloc.c:4592
__alloc_pages_node include/linux/gfp.h:238 [inline]
alloc_pages_node include/linux/gfp.h:261 [inline]
alloc_slab_page mm/slub.c:2175 [inline]
allocate_slab mm/slub.c:2338 [inline]
new_slab+0x2de/0x1400 mm/slub.c:2391
___slab_alloc+0x1184/0x33d0 mm/slub.c:3525
__slab_alloc mm/slub.c:3610 [inline]
__slab_alloc_node mm/slub.c:3663 [inline]
slab_alloc_node mm/slub.c:3835 [inline]
kmem_cache_alloc+0x6d3/0xbe0 mm/slub.c:3852
reqsk_alloc include/net/request_sock.h:131 [inline]
inet_reqsk_alloc+0x66/0x7a0 net/ipv4/tcp_input.c:6978
tcp_conn_request+0x484/0x44e0 net/ipv4/tcp_input.c:7135
tcp_v4_conn_request+0x16f/0x1d0 net/ipv4/tcp_ipv4.c:1716
tcp_rcv_state_process+0x2e5/0x4bb0 net/ipv4/tcp_input.c:6655
tcp_v4_do_rcv+0xbfd/0x10b0 net/ipv4/tcp_ipv4.c:1929
tcp_v4_rcv+0x4ce4/0x5420 net/ipv4/tcp_ipv4.c:2322
ip_protocol_deliver_rcu+0x2a3/0x13d0 net/ipv4/ip_input.c:205
ip_local_deliver_finish+0x332/0x500 net/ipv4/ip_input.c:233
NF_HOOK include/linux/netfilter.h:314 [inline]
ip_local_deliver+0x21f/0x490 net/ipv4/ip_input.c:254
dst_input include/net/dst.h:460 [inline]
ip_sublist_rcv_finish net/ipv4/ip_input.c:580 [inline]
ip_list_rcv_finish net/ipv4/ip_input.c:631 [inline]
ip_sublist_rcv+0x15f3/0x17f0 net/ipv4/ip_input.c:639
ip_list_rcv+0x9ef/0xa40 net/ipv4/ip_input.c:674
__netif_receive_skb_list_ptype net/core/dev.c:5581 [inline]
__netif_receive_skb_list_core+0x15c5/0x1670 net/core/dev.c:5629
__netif_receive_skb_list net/core/dev.c:5681 [inline]
netif_receive_skb_list_internal+0x106c/0x16f0 net/core/dev.c:5773
gro_normal_list include/net/gro.h:438 [inline]
napi_complete_done+0x425/0x880 net/core/dev.c:6113
virtqueue_napi_complete drivers/net/virtio_net.c:465 [inline]
virtnet_poll+0x149d/0x2240 drivers/net/virtio_net.c:2211
__napi_poll+0xe7/0x980 net/core/dev.c:6632
napi_poll net/core/dev.c:6701 [inline]
net_rx_action+0x89d/0x1820 net/core/dev.c:6813
__do_softirq+0x1c0/0x7d7 kernel/softirq.c:554
CPU: 0 PID: 16792 Comm: syz-executor.2 Not tainted
6.8.0-syzkaller-05562-g61387b8dcf1d #0
Hardware name: Google Google Compute Engine/Google Compute Engine,
BIOS Google 02/29/2024
