linux-kernel - network card doesn't recovered itself after a SYN flooding attack

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Message-ID: <56519E2B.8050500@gmx.de>
Date:	Sun, 22 Nov 2015 11:51:23 +0100
From:	Toralf Förster <toralf.foerster@....de>
To:	Linux Kernel <linux-kernel@...r.kernel.org>
Subject: network card doesn't recovered itself after a SYN flooding attack

At 22th of November at 21:26 UTC my server (64 bit stable Gentoo hardened) suffered from a DDoS attack. 

>From the kern.log:

	
Nov 20 22:26:29 tor-relay kernel: [2431358.124515] TCP: request_sock_TCP: Possible SYN flooding on port 80. Sending cookies.  Check SNMP counters.
Nov 20 22:26:48 tor-relay kernel: [2431377.216133] ------------[ cut here ]------------
Nov 20 22:26:48 tor-relay kernel: [2431377.216141] WARNING: CPU: 7 PID: 12421 at net/sched/sch_generic.c:303 dev_watchdog+0x272/0x280()
Nov 20 22:26:48 tor-relay kernel: [2431377.216143] NETDEV WATCHDOG: enp3s0 (r8169): transmit queue 0 timed out
Nov 20 22:26:48 tor-relay kernel: [2431377.216145] Modules linked in:
Nov 20 22:26:48 tor-relay kernel: [2431377.216148]  af_packet nf_log_ipv6 nf_conntrack_ipv6 nf_defrag_ipv6 ip6table_filter ip6_tables nf_log_ipv4 nf_log_common xt_LOG xt_multiport nf_conntrack_ipv4 nf_defrag_ipv4 xt_conntrack nf_conntrack iptable_filter ip_tables i2c_i801 i2c_core tpm_tis tpm thermal processor battery atkbd x86_pkg_temp_thermal button microcode fan
Nov 20 22:26:48 tor-relay kernel: [2431377.216173] CPU: 7 PID: 12421 Comm: emerge Not tainted 4.1.7-hardened-r1 #1
Nov 20 22:26:48 tor-relay kernel: [2431377.216174] Hardware name: System manufacturer System Product Name/P8H77-M PRO, BIOS 0922 09/10/2012
Nov 20 22:26:48 tor-relay kernel: [2431377.216176]  ffffffff994fa966 0000000000000000 ffffffff99bced09 ffff88041fbc3d18
Nov 20 22:26:48 tor-relay kernel: [2431377.216179]  ffffffff99983e26 0000000000000000 ffff88041fbc3d68 ffff88041fbc3d58
Nov 20 22:26:48 tor-relay kernel: [2431377.216182]  ffffffff9947f08a ffff88041fbc3d48 ffffffff99bced09 000000000000012f
Nov 20 22:26:48 tor-relay kernel: [2431377.216185] Call Trace:
Nov 20 22:26:48 tor-relay kernel: [2431377.216187]    [] ? print_modules+0x76/0xe0
Nov 20 22:26:48 tor-relay kernel: [2431377.216198]  [] dump_stack+0x45/0x5d
Nov 20 22:26:48 tor-relay kernel: [2431377.216203]  [] warn_slowpath_common+0x8a/0xd0
Nov 20 22:26:48 tor-relay kernel: [2431377.216205]  [] warn_slowpath_fmt+0x5a/0x70
Nov 20 22:26:48 tor-relay kernel: [2431377.216210]  [] ? task_tick_fair+0x2a8/0x760
Nov 20 22:26:48 tor-relay kernel: [2431377.216213]  [] dev_watchdog+0x272/0x280
Nov 20 22:26:48 tor-relay kernel: [2431377.216216]  [] ? dev_deactivate_queue+0x70/0x70
Nov 20 22:26:48 tor-relay kernel: [2431377.216219]  [] call_timer_fn+0x47/0x140
Nov 20 22:26:48 tor-relay kernel: [2431377.216222]  [] run_timer_softirq+0x291/0x450
Nov 20 22:26:48 tor-relay kernel: [2431377.216224]  [] ? dev_deactivate_queue+0x70/0x70
Nov 20 22:26:48 tor-relay kernel: [2431377.216228]  [] __do_softirq+0xf8/0x290
Nov 20 22:26:48 tor-relay kernel: [2431377.216230]  [] irq_exit+0x9d/0xb0
Nov 20 22:26:48 tor-relay kernel: [2431377.216235]  [] smp_apic_timer_interrupt+0x55/0x70
Nov 20 22:26:48 tor-relay kernel: [2431377.216237]  [] apic_timer_interrupt+0x97/0xa0
Nov 20 22:26:48 tor-relay kernel: [2431377.216239]  
Nov 20 22:26:48 tor-relay kernel: [2431377.216241] ---[ end trace 93431a9382c0a11a ]---
Nov 20 22:26:48 tor-relay kernel: [2431377.237826] r8169 0000:03:00.0 enp3s0: link up
Nov 20 22:28:18 tor-relay kernel: [2431467.175659] r8169 0000:03:00.0 enp3s0: link up
Nov 20 22:28:30 tor-relay kernel: [2431479.172562] r8169 0000:03:00.0 enp3s0: link up
Nov 20 22:28:42 tor-relay kernel: [2431491.164472] r8169 0000:03:00.0 enp3s0: link up
Nov 20 22:28:54 tor-relay kernel: [2431503.170416] r8169 0000:03:00.0 enp3s0: link up
Nov 20 22:29:06 tor-relay kernel: [2431515.148333] r8169 0000:03:00.0 enp3s0: link up
Nov 20 22:29:18 tor-relay kernel: [2431527.143293] r8169 0000:03:00.0 enp3s0: link up
Nov 20 22:29:30 tor-relay kernel: [2431539.142164] r8169 0000:03:00.0 enp3s0: link up
Nov 20 22:29:42 tor-relay kernel: [2431551.124104] r8169 0000:03:00.0 enp3s0: link up
...
Nov 22 10:56:24 tor-relay kernel: [2562675.624512] r8169 0000:03:00.0 enp3s0: link up
  


The last line repeated and the network was down till I initiated a hardware reset.

It looks for me that the attack turned the network card into a state from which it couldn't recovered itself, or ? 
Anything what I should change here at the system to avoid such a hang ?

-- 
Toralf, pgp key: C4EACDDE 0076E94E
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