linux.git/net/ipv4/syncookies.c, branch v6.15

tcp: be less liberal in TSEcr received while in SYN_RECV state

2025-02-27T02:11:17+00:00

Yong-Hao Zou mentioned that linux was not strict as other OS in 3WHS,
for flows using TCP TS option (RFC 7323)

As hinted by an old comment in tcp_check_req(),
we can check the TSEcr value in the incoming packet corresponds
to one of the SYNACK TSval values we have sent.

In this patch, I record the oldest and most recent values
that SYNACK packets have used.

Send a challenge ACK if we receive a TSEcr outside
of this range, and increase a new SNMP counter.

nstat -az | grep TSEcrRejected
TcpExtTSEcrRejected            0                  0.0

Due to TCP fastopen implementation, do not apply yet these checks
for fastopen flows.

v2: No longer use req->num_timeout, but treq->snt_tsval_first
    to detect when first SYNACK is prepared. This means
    we make sure to not send an initial zero TSval.
    Make sure MPTCP and TCP selftests are passing.
    Change MIB name to TcpExtTSEcrRejected

v1: https://lore.kernel.org/netdev/CADVnQykD8i4ArpSZaPKaoNxLJ2if2ts9m4As+=Jvdkrgx1qMHw@mail.gmail.com/T/

Reported-by: Yong-Hao Zou 
Signed-off-by: Eric Dumazet 
Reviewed-by: Matthieu Baerts (NGI0) 
Reviewed-by: Neal Cardwell 
Reviewed-by: Kuniyuki Iwashima 
Link: https://patch.msgid.link/20250225171048.3105061-1-edumazet@google.com
Signed-off-by: Jakub Kicinski

tcp: use EXPORT_IPV6_MOD[_GPL]()

2025-02-14T21:09:39+00:00

Use EXPORT_IPV6_MOD[_GPL]() for symbols that don't need
to be exported unless CONFIG_IPV6=m

tcp_hashinfo and tcp_openreq_init_rwin() are no longer
used from any module anyway.

Signed-off-by: Eric Dumazet 
Reviewed-by: Kuniyuki Iwashima 
Reviewed-by: Mateusz Polchlopek 
Link: https://patch.msgid.link/20250212132418.1524422-4-edumazet@google.com
Signed-off-by: Jakub Kicinski

tcp: use sk_skb_reason_drop to free rx packets

2024-06-19T11:44:22+00:00

Replace kfree_skb_reason with sk_skb_reason_drop and pass the receiving
socket to the tracepoint.

Reported-by: kernel test robot 
Closes: https://lore.kernel.org/r/202406011539.jhwBd7DX-lkp@intel.com/
Signed-off-by: Yan Zhai 
Acked-by: Jesper Dangaard Brouer 
Signed-off-by: David S. Miller

tcp: annotate data-races around tp->window_clamp

2024-04-06T05:32:37+00:00

tp->window_clamp can be read locklessly, add READ_ONCE()
and WRITE_ONCE() annotations.

Signed-off-by: Eric Dumazet 
Reviewed-by: Jason Xing 
Link: https://lore.kernel.org/r/20240404114231.2195171-1-edumazet@google.com
Signed-off-by: Jakub Kicinski

tcp: Clear req->syncookie in reqsk_alloc().

2024-03-20T02:35:59+00:00

syzkaller reported a read of uninit req->syncookie. [0]

Originally, req->syncookie was used only in tcp_conn_request()
to indicate if we need to encode SYN cookie in SYN+ACK, so the
field remains uninitialised in other places.

The commit 695751e31a63 ("bpf: tcp: Handle BPF SYN Cookie in
cookie_v[46]_check().") added another meaning in ACK path;
req->syncookie is set true if SYN cookie is validated by BPF
kfunc.

After the change, cookie_v[46]_check() always read req->syncookie,
but it is not initialised in the normal SYN cookie case as reported
by KMSAN.

Let's make sure we always initialise req->syncookie in reqsk_alloc().

[0]:
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

Fixes: 695751e31a63 ("bpf: tcp: Handle BPF SYN Cookie in cookie_v[46]_check().")
Reported-by: syzkaller 
Reported-by: Eric Dumazet 
Closes: https://lore.kernel.org/bpf/CANn89iKdN9c+C_2JAUbc+VY3DDQjAQukMtiBbormAmAk9CdvQA@mail.gmail.com/
Signed-off-by: Kuniyuki Iwashima 
Reviewed-by: Eric Dumazet 
Acked-by: Martin KaFai Lau 
Link: https://lore.kernel.org/r/20240315224710.55209-1-kuniyu@amazon.com
Signed-off-by: Jakub Kicinski

tcp: use drop reasons in cookie check for ipv4

2024-02-28T10:39:21+00:00

Now it's time to use the prepared definitions to refine this part.
Four reasons used might enough for now, I think.

Signed-off-by: Jason Xing 
Reviewed-by: Eric Dumazet 
Reviewed-by: David Ahern 
Reviewed-by: Kuniyuki Iwashima 
Signed-off-by: David S. Miller

tcp: directly drop skb in cookie check for ipv4

2024-02-28T10:39:21+00:00

Only move the skb drop from tcp_v4_do_rcv() to cookie_v4_check() itself,
no other changes made. It can help us refine the specific drop reasons
later.

Signed-off-by: Jason Xing 
Reviewed-by: Kuniyuki Iwashima 
Reviewed-by: Eric Dumazet 
Reviewed-by: David Ahern 
Signed-off-by: David S. Miller

bpf: tcp: Handle BPF SYN Cookie in cookie_v[46]_check().

2024-01-23T22:40:24+00:00

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.

Signed-off-by: Kuniyuki Iwashima 
Link: https://lore.kernel.org/r/20240115205514.68364-5-kuniyu@amazon.com
Signed-off-by: Martin KaFai Lau 
Signed-off-by: Alexei Starovoitov

tcp: Move tcp_ns_to_ts() to tcp.h

2024-01-23T22:40:23+00:00

We will support arbitrary SYN Cookie with BPF.

When BPF prog validates ACK and kfunc allocates a reqsk, we need
to call tcp_ns_to_ts() to calculate an offset of TSval for later
use:

  time
  t0 : Send SYN+ACK
       -> tsval = Initial TSval (Random Number)

  t1 : Recv ACK of 3WHS
       -> tsoff = TSecr - tcp_ns_to_ts(usec_ts_ok, tcp_clock_ns())
                = Initial TSval - t1

  t2 : Send ACK
       -> tsval = t2 + tsoff
                = Initial TSval + (t2 - t1)
                = Initial TSval + Time Delta (x)

  (x) Note that the time delta does not include the initial RTT
      from t0 to t1.

Let's move tcp_ns_to_ts() to tcp.h.

Signed-off-by: Kuniyuki Iwashima 
Reviewed-by: Eric Dumazet 
Link: https://lore.kernel.org/r/20240115205514.68364-2-kuniyu@amazon.com
Signed-off-by: Martin KaFai Lau 
Signed-off-by: Alexei Starovoitov

tcp: Factorise cookie-dependent fields initialisation in cookie_v[46]_check()

2023-11-30T04:16:38+00:00

We will support arbitrary SYN Cookie with BPF, and then kfunc at
TC will preallocate reqsk and initialise some fields that should
not be overwritten later by cookie_v[46]_check().

To simplify the flow in cookie_v[46]_check(), we move such fields'
initialisation to cookie_tcp_reqsk_alloc() and factorise non-BPF
SYN Cookie handling into cookie_tcp_check(), where we validate the
cookie and allocate reqsk, as done by kfunc later.

Note that we set ireq->ecn_ok in two steps, the latter of which will
be shared by the BPF case.  As cookie_ecn_ok() is one-liner, now
it's inlined.

Signed-off-by: Kuniyuki Iwashima 
Reviewed-by: Simon Horman 
Reviewed-by: Eric Dumazet 
Link: https://lore.kernel.org/r/20231129022924.96156-9-kuniyu@amazon.com
Signed-off-by: Jakub Kicinski