| 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> |
| @@ -932,6 +933,30 @@ 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 |
| @@ -958,6 +983,11 @@ 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), |