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Subject: net: sysrq via icmp
From: Carsten Emde <C.Emde@osadl.org>
Date: Tue, 19 Jul 2011 13:51:17 +0100
There are (probably rare) situations when a system crashed and the system
console becomes unresponsive but the network icmp layer still is alive.
Wouldn't it be wonderful, if we then could submit a sysreq command via ping?
This patch provides this facility. Please consult the updated documentation
Documentation/sysrq.txt for details.
Signed-off-by: Carsten Emde <C.Emde@osadl.org>
---
Documentation/admin-guide/sysrq.rst | 12 ++++++++++++
include/net/netns/ipv4.h | 1 +
net/ipv4/icmp.c | 30 ++++++++++++++++++++++++++++++
net/ipv4/sysctl_net_ipv4.c | 7 +++++++
4 files changed, 50 insertions(+)
--- a/Documentation/admin-guide/sysrq.rst
+++ b/Documentation/admin-guide/sysrq.rst
@@ -77,6 +77,18 @@ On all
echo t > /proc/sysrq-trigger
+On all
+ Enable network SysRq by writing a cookie to icmp_echo_sysrq, e.g.::
+
+ echo 0x01020304 >/proc/sys/net/ipv4/icmp_echo_sysrq
+
+ Send an ICMP echo request with this pattern plus the particular
+ SysRq command key. Example::
+
+ ping -c1 -s57 -p0102030468
+
+ will trigger the SysRq-H (help) command.
+
What are the 'command' keys?
~~~~~~~~~~~~~~~~~~~~~~~~~~~~
--- a/include/net/netns/ipv4.h
+++ b/include/net/netns/ipv4.h
@@ -79,6 +79,7 @@ struct netns_ipv4 {
int sysctl_icmp_echo_ignore_all;
int sysctl_icmp_echo_ignore_broadcasts;
+ int sysctl_icmp_echo_sysrq;
int sysctl_icmp_ignore_bogus_error_responses;
int sysctl_icmp_ratelimit;
int sysctl_icmp_ratemask;
--- a/net/ipv4/icmp.c
+++ b/net/ipv4/icmp.c
@@ -69,6 +69,7 @@
#include <linux/jiffies.h>
#include <linux/kernel.h>
#include <linux/fcntl.h>
+#include <linux/sysrq.h>
#include <linux/socket.h>
#include <linux/in.h>
#include <linux/inet.h>
@@ -927,6 +928,30 @@ static bool icmp_redirect(struct sk_buff
}
/*
+ * 32bit and 64bit have different timestamp length, so we check for
+ * the cookie at offset 20 and verify it is repeated at offset 50
+ */
+#define CO_POS0 20
+#define CO_POS1 50
+#define CO_SIZE sizeof(int)
+#define ICMP_SYSRQ_SIZE 57
+
+/*
+ * We got a ICMP_SYSRQ_SIZE sized ping request. Check for the cookie
+ * pattern and if it matches send the next byte as a trigger to sysrq.
+ */
+static void icmp_check_sysrq(struct net *net, struct sk_buff *skb)
+{
+ int cookie = htonl(net->ipv4.sysctl_icmp_echo_sysrq);
+ char *p = skb->data;
+
+ if (!memcmp(&cookie, p + CO_POS0, CO_SIZE) &&
+ !memcmp(&cookie, p + CO_POS1, CO_SIZE) &&
+ p[CO_POS0 + CO_SIZE] == p[CO_POS1 + CO_SIZE])
+ handle_sysrq(p[CO_POS0 + CO_SIZE]);
+}
+
+/*
* Handle ICMP_ECHO ("ping") requests.
*
* RFC 1122: 3.2.2.6 MUST have an echo server that answers ICMP echo
@@ -953,6 +978,11 @@ static bool icmp_echo(struct sk_buff *sk
icmp_param.data_len = skb->len;
icmp_param.head_len = sizeof(struct icmphdr);
icmp_reply(&icmp_param, skb);
+
+ if (skb->len == ICMP_SYSRQ_SIZE &&
+ net->ipv4.sysctl_icmp_echo_sysrq) {
+ icmp_check_sysrq(net, skb);
+ }
}
/* should there be an ICMP stat for ignored echos? */
return true;
--- a/net/ipv4/sysctl_net_ipv4.c
+++ b/net/ipv4/sysctl_net_ipv4.c
@@ -687,6 +687,13 @@ static struct ctl_table ipv4_net_table[]
.proc_handler = proc_dointvec
},
{
+ .procname = "icmp_echo_sysrq",
+ .data = &init_net.ipv4.sysctl_icmp_echo_sysrq,
+ .maxlen = sizeof(int),
+ .mode = 0644,
+ .proc_handler = proc_dointvec
+ },
+ {
.procname = "icmp_ignore_bogus_error_responses",
.data = &init_net.ipv4.sysctl_icmp_ignore_bogus_error_responses,
.maxlen = sizeof(int),
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