BMC/Intel-BMC/linux.git/net/ipv4/tcp_fastopen.c, branch v4.4

tcp/dccp: fix hashdance race for passive sessions

2015-10-23T12:42:21+00:00

Multiple cpus can process duplicates of incoming ACK messages matching a SYN_RECV request socket. This is a rare event under normal operations, but definitely can happen. Only one must win the race, otherwise corruption would occur. To fix this without adding new atomic ops, we use logic in inet_ehash_nolisten() to detect the request was present in the same ehash bucket where we try to insert the new child. If request socket was not found, we have to undo the child creation. This actually removes a spin_lock()/spin_unlock() pair in reqsk_queue_unlink() for the fast path. Fixes: e994b2f0fb92 ("tcp: do not lock listener to process SYN packets") Fixes: 079096f103fa ("tcp/dccp: install syn_recv requests into ehash table") Signed-off-by: Eric Dumazet Signed-off-by: David S. Miller

tcp: fix fastopen races vs lockless listener

2015-10-05T09:45:24+00:00

There are multiple races that need fixes : 1) skb_get() + queue skb + kfree_skb() is racy An accept() can be done on another cpu, data consumed immediately. tcp_recvmsg() uses __kfree_skb() as it is assumed all skb found in socket receive queue are private. Then the kfree_skb() in tcp_rcv_state_process() uses an already freed skb 2) tcp_reqsk_record_syn() needs to be done before tcp_try_fastopen() for the same reasons. 3) We want to send the SYNACK before queueing child into accept queue, otherwise we might reintroduce the ooo issue fixed in commit 7c85af881044 ("tcp: avoid reorders for TFO passive connections") Signed-off-by: Eric Dumazet Signed-off-by: David S. Miller

tcp: attach SYNACK messages to request sockets instead of listener

2015-10-03T11:32:43+00:00

If a listen backlog is very big (to avoid syncookies), then the listener sk->sk_wmem_alloc is the main source of false sharing, as we need to touch it twice per SYNACK re-transmit and TX completion. (One SYN packet takes listener lock once, but up to 6 SYNACK are generated) By attaching the skb to the request socket, we remove this source of contention. Tested: listen(fd, 10485760); // single listener (no SO_REUSEPORT) 16 RX/TX queue NIC Sustain a SYNFLOOD attack of ~320,000 SYN per second, Sending ~1,400,000 SYNACK per second. Perf profiles now show listener spinlock being next bottleneck. 20.29% [kernel] [k] queued_spin_lock_slowpath 10.06% [kernel] [k] __inet_lookup_established 5.12% [kernel] [k] reqsk_timer_handler 3.22% [kernel] [k] get_next_timer_interrupt 3.00% [kernel] [k] tcp_make_synack 2.77% [kernel] [k] ipt_do_table 2.70% [kernel] [k] run_timer_softirq 2.50% [kernel] [k] ip_finish_output 2.04% [kernel] [k] cascade Signed-off-by: Eric Dumazet Signed-off-by: David S. Miller

tcp: prepare fastopen code for upcoming listener changes

2015-09-29T23:53:10+00:00

While auditing TCP stack for upcoming 'lockless' listener changes, I found I had to change fastopen_init_queue() to properly init the object before publishing it. Otherwise an other cpu could try to lock the spinlock before it gets properly initialized. Instead of adding appropriate barriers, just remove dynamic memory allocations : - Structure is 28 bytes on 64bit arches. Using additional 8 bytes for holding a pointer seems overkill. - Two listeners can share same cache line and performance would suffer. If we really want to save few bytes, we would instead dynamically allocate whole struct request_sock_queue in the future. Signed-off-by: Eric Dumazet Signed-off-by: David S. Miller

tcp: avoid reorders for TFO passive connections

2015-09-29T05:11:19+00:00

We found that a TCP Fast Open passive connection was vulnerable to reorders, as the exchange might look like [1] C -> S S [2] S -> C S. ack request [3] S -> C . packets [2] and [3] can be generated at almost the same time. If C receives the 3rd packet before the 2nd, it will drop it as the socket is in SYN_SENT state and expects a SYNACK. S will have to retransmit the answer. Current OOO avoidance in linux is defeated because SYNACK packets are attached to the LISTEN socket, while DATA packets are attached to the children. They might be sent by different cpus, and different TX queues might be selected. It turns out that for TFO, we created a child, which is a full blown socket in TCP_SYN_RECV state, and we simply can attach the SYNACK packet to this socket. This means that at the time tcp_sendmsg() pushes DATA packet, skb->ooo_okay will be set iff the SYNACK packet had been sent and TX completed. This removes the reorder source at the host level. We also removed the export of tcp_try_fastopen(), as it is no longer called from IPv6. Signed-off-by: Eric Dumazet Signed-off-by: Yuchung Cheng Signed-off-by: David S. Miller

tcp: Do not call tcp_fastopen_reset_cipher from interrupt context

2015-06-23T09:38:10+00:00

tcp_fastopen_reset_cipher really cannot be called from interrupt context. It allocates the tcp_fastopen_context with GFP_KERNEL and calls crypto_alloc_cipher, which allocates all kind of stuff with GFP_KERNEL. Thus, we might sleep when the key-generation is triggered by an incoming TFO cookie-request which would then happen in interrupt- context, as shown by enabling CONFIG_DEBUG_ATOMIC_SLEEP: [ 36.001813] BUG: sleeping function called from invalid context at mm/slub.c:1266 [ 36.003624] in_atomic(): 1, irqs_disabled(): 0, pid: 1016, name: packetdrill [ 36.004859] CPU: 1 PID: 1016 Comm: packetdrill Not tainted 4.1.0-rc7 #14 [ 36.006085] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS rel-1.7.5-0-ge51488c-20140602_164612-nilsson.home.kraxel.org 04/01/2014 [ 36.008250] 00000000000004f2 ffff88007f8838a8 ffffffff8171d53a ffff880075a084a8 [ 36.009630] ffff880075a08000 ffff88007f8838c8 ffffffff810967d3 ffff88007f883928 [ 36.011076] 0000000000000000 ffff88007f8838f8 ffffffff81096892 ffff88007f89be00 [ 36.012494] Call Trace: [ 36.012953] [] dump_stack+0x4f/0x6d [ 36.014085] [] ___might_sleep+0x103/0x170 [ 36.015117] [] __might_sleep+0x52/0x90 [ 36.016117] [] kmem_cache_alloc_trace+0x47/0x190 [ 36.017266] [] ? tcp_fastopen_reset_cipher+0x42/0x130 [ 36.018485] [] tcp_fastopen_reset_cipher+0x42/0x130 [ 36.019679] [] tcp_fastopen_init_key_once+0x61/0x70 [ 36.020884] [] __tcp_fastopen_cookie_gen+0x1c/0x60 [ 36.022058] [] tcp_try_fastopen+0x58f/0x730 [ 36.023118] [] tcp_conn_request+0x3e8/0x7b0 [ 36.024185] [] ? __module_text_address+0x12/0x60 [ 36.025327] [] tcp_v4_conn_request+0x51/0x60 [ 36.026410] [] tcp_rcv_state_process+0x190/0xda0 [ 36.027556] [] ? __inet_lookup_established+0x47/0x170 [ 36.028784] [] tcp_v4_do_rcv+0x16d/0x3d0 [ 36.029832] [] ? security_sock_rcv_skb+0x16/0x20 [ 36.030936] [] tcp_v4_rcv+0x77a/0x7b0 [ 36.031875] [] ? iptable_filter_hook+0x33/0x70 [ 36.032953] [] ip_local_deliver_finish+0x92/0x1f0 [ 36.034065] [] ip_local_deliver+0x9a/0xb0 [ 36.035069] [] ? ip_rcv+0x3d0/0x3d0 [ 36.035963] [] ip_rcv_finish+0x119/0x330 [ 36.036950] [] ip_rcv+0x2e7/0x3d0 [ 36.037847] [] __netif_receive_skb_core+0x552/0x930 [ 36.038994] [] __netif_receive_skb+0x27/0x70 [ 36.040033] [] process_backlog+0xd2/0x1f0 [ 36.041025] [] net_rx_action+0x122/0x310 [ 36.042007] [] __do_softirq+0x103/0x2f0 [ 36.042978] [] do_softirq_own_stack+0x1c/0x30 This patch moves the call to tcp_fastopen_init_key_once to the places where a listener socket creates its TFO-state, which always happens in user-context (either from the setsockopt, or implicitly during the listen()-call) Cc: Eric Dumazet Cc: Hannes Frederic Sowa Fixes: 222e83d2e0ae ("tcp: switch tcp_fastopen key generation to net_get_random_once") Signed-off-by: Christoph Paasch Acked-by: Eric Dumazet Signed-off-by: David S. Miller

tcp: fix a potential deadlock in tcp_get_info()

2015-05-22T17:46:06+00:00

Taking socket spinlock in tcp_get_info() can deadlock, as inet_diag_dump_icsk() holds the &hashinfo->ehash_locks[i], while packet processing can use the reverse locking order. We could avoid this locking for TCP_LISTEN states, but lockdep would certainly get confused as all TCP sockets share same lockdep classes. [ 523.722504] ====================================================== [ 523.728706] [ INFO: possible circular locking dependency detected ] [ 523.734990] 4.1.0-dbg-DEV #1676 Not tainted [ 523.739202] ------------------------------------------------------- [ 523.745474] ss/18032 is trying to acquire lock: [ 523.750002] (slock-AF_INET){+.-...}, at: [] tcp_get_info+0x2c4/0x360 [ 523.758129] [ 523.758129] but task is already holding lock: [ 523.763968] (&(&hashinfo->ehash_locks[i])->rlock){+.-...}, at: [] inet_diag_dump_icsk+0x1d5/0x6c0 [ 523.774661] [ 523.774661] which lock already depends on the new lock. [ 523.774661] [ 523.782850] [ 523.782850] the existing dependency chain (in reverse order) is: [ 523.790326] -> #1 (&(&hashinfo->ehash_locks[i])->rlock){+.-...}: [ 523.796599] [] lock_acquire+0xbb/0x270 [ 523.802565] [] _raw_spin_lock+0x38/0x50 [ 523.808628] [] __inet_hash_nolisten+0x78/0x110 [ 523.815273] [] tcp_v4_syn_recv_sock+0x24b/0x350 [ 523.822067] [] tcp_check_req+0x3c1/0x500 [ 523.828199] [] tcp_v4_do_rcv+0x239/0x3d0 [ 523.834331] [] tcp_v4_rcv+0xa8e/0xc10 [ 523.840202] [] ip_local_deliver_finish+0x133/0x3e0 [ 523.847214] [] ip_local_deliver+0xaa/0xc0 [ 523.853440] [] ip_rcv_finish+0x168/0x5c0 [ 523.859624] [] ip_rcv+0x307/0x420 Lets use u64_sync infrastructure instead. As a bonus, 64bit arches get optimized, as these are nop for them. Fixes: 0df48c26d841 ("tcp: add tcpi_bytes_acked to tcp_info") Signed-off-by: Eric Dumazet Signed-off-by: David S. Miller

tcp: add tcpi_bytes_received to tcp_info

2015-04-29T21:10:37+00:00

This patch tracks total number of payload bytes received on a TCP socket. This is the sum of all changes done to tp->rcv_nxt RFC4898 named this : tcpEStatsAppHCThruOctetsReceived This is a 64bit field, and can be fetched both from TCP_INFO getsockopt() if one has a handle on a TCP socket, or from inet_diag netlink facility (iproute2/ss patch will follow) Note that tp->bytes_received was placed near tp->rcv_nxt for best data locality and minimal performance impact. Signed-off-by: Eric Dumazet Cc: Yuchung Cheng Cc: Matt Mathis Cc: Eric Salo Cc: Martin Lau Cc: Chris Rapier Acked-by: Yuchung Cheng Signed-off-by: David S. Miller

tcp: RFC7413 option support for Fast Open server

2015-04-07T22:36:39+00:00

Fast Open has been using the experimental option with a magic number (RFC6994) to request and grant Fast Open cookies. This patch enables the server to support the official IANA option 34 in RFC7413 in addition. The change has passed all existing Fast Open tests with both old and new options at Google. Signed-off-by: Daniel Lee Signed-off-by: Yuchung Cheng Signed-off-by: Neal Cardwell Signed-off-by: David S. Miller

ipv4: coding style: comparison for equality with NULL

2015-04-03T16:11:15+00:00

The ipv4 code uses a mixture of coding styles. In some instances check for NULL pointer is done as x == NULL and sometimes as !x. !x is preferred according to checkpatch and this patch makes the code consistent by adopting the latter form. No changes detected by objdiff. Signed-off-by: Ian Morris Signed-off-by: David S. Miller