From 44dd1353575f9f1da93338d280e6765dc5e209cc Mon Sep 17 00:00:00 2001 From: Carsten Emde Date: Tue, 19 Jul 2011 13:51:17 +0100 Subject: [PATCH 241/365] net: sysrq via icmp 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 --- Documentation/sysrq.txt | 11 +++++++++-- include/net/netns/ipv4.h | 1 + net/ipv4/icmp.c | 30 ++++++++++++++++++++++++++++++ net/ipv4/sysctl_net_ipv4.c | 7 +++++++ 4 files changed, 47 insertions(+), 2 deletions(-) diff --git a/Documentation/sysrq.txt b/Documentation/sysrq.txt index 3a3b30ac2a75..9e0745cafbd8 100644 --- a/Documentation/sysrq.txt +++ b/Documentation/sysrq.txt @@ -59,10 +59,17 @@ On PowerPC - Press 'ALT - Print Screen (or F13) - , On other - If you know of the key combos for other architectures, please let me know so I can add them to this section. -On all - write a character to /proc/sysrq-trigger. e.g.: - +On all - write a character to /proc/sysrq-trigger, e.g.: 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? ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ 'b' - Will immediately reboot the system without syncing or unmounting diff --git a/include/net/netns/ipv4.h b/include/net/netns/ipv4.h index af1c5e7c7e94..faf4a8cd61e6 100644 --- a/include/net/netns/ipv4.h +++ b/include/net/netns/ipv4.h @@ -70,6 +70,7 @@ 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; diff --git a/net/ipv4/icmp.c b/net/ipv4/icmp.c index bd6a58c725b5..c79ad4ba670a 100644 --- a/net/ipv4/icmp.c +++ b/net/ipv4/icmp.c @@ -69,6 +69,7 @@ #include #include #include +#include #include #include #include @@ -914,6 +915,30 @@ static bool icmp_redirect(struct sk_buff *skb) return true; } +/* + * 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. * @@ -941,6 +966,11 @@ static bool icmp_echo(struct sk_buff *skb) 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; diff --git a/net/ipv4/sysctl_net_ipv4.c b/net/ipv4/sysctl_net_ipv4.c index 22436858b534..c29d8662e961 100644 --- a/net/ipv4/sysctl_net_ipv4.c +++ b/net/ipv4/sysctl_net_ipv4.c @@ -716,6 +716,13 @@ static struct ctl_table ipv4_net_table[] = { .mode = 0644, .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, -- 2.28.0